BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. 32 YEARS OF CHANGES IN PASSERINE NUMBERS DURING SPRING AND FALL MIGRATIONS IN COASTAL MASSACHUSETTS Author(s): TREVOR L. LLOYD-EVANS and JONATHAN L. ATWOOD Source: The Wilson Bulletin, 116(1):1-16. 2004. Published By: The Wilson Ornithological Society DOI: http://dx.doi.org/10.1676/0043-5643(2004)116[0001:YOCIPN]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.1676/0043-5643%282004%29116%5B0001%3AYOCIPN %5D2.0.CO%3B2 BioOne (www.bioone.org ) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use . Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.
Transcript
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors nonprofit publishers academic institutions researchlibraries and research funders in the common goal of maximizing access to critical research
32 YEARS OF CHANGES IN PASSERINE NUMBERS DURING SPRING ANDFALL MIGRATIONS IN COASTAL MASSACHUSETTSAuthor(s) TREVOR L LLOYD-EVANS and JONATHAN L ATWOODSource The Wilson Bulletin 116(1)1-16 2004Published By The Wilson Ornithological SocietyDOI httpdxdoiorg1016760043-5643(2004)116[0001YOCIPN]20CO2URL httpwwwbiooneorgdoifull1016760043-5643282004291165B00013AYOCIPN5D20CO3B2
BioOne (wwwbiooneorg) is a nonprofit online aggregation of core research in the biological ecological andenvironmental sciences BioOne provides a sustainable online platform for over 170 journals and books publishedby nonprofit societies associations museums institutions and presses
Your use of this PDF the BioOne Web site and all posted and associated content indicates your acceptance ofBioOnersquos Terms of Use available at wwwbiooneorgpageterms_of_use
Usage of BioOne content is strictly limited to personal educational and non-commercial use Commercial inquiriesor rights and permissions requests should be directed to the individual publisher as copyright holder
1
THE WILSON BULLETINA QUARTERLY JOURNAL OF ORNITHOLOGY
Published by the Wilson Ornithological Society
VOL 116 NO 1 PAGES 1ndash118March 2004
Wilson Bulletin 116(1) 2004 pp 1ndash16
32 YEARS OF CHANGES IN PASSERINE NUMBERSDURING SPRING AND FALL MIGRATIONS
IN COASTAL MASSACHUSETTS
TREVOR L LLOYD-EVANS13 AND JONATHAN L ATWOOD12
ABSTRACTmdashUsing standardized mist-net captures collected over a 32-year period (1970ndash2001) we ex-amined changes in the capture rates of passerines recorded in coastal Massachusetts during fall (78 species) andspring (72 species) migration Capture rates of 45 species of fall migrants (58) declined significantly betweenearly (1970ndash1985) and late (1986ndash2001) years of the study 36 species of spring migrants (50) showed sig-nificant declines Only Carolina Wren (Thryothorus ludovicianus) Tufted Titmouse (Baeolophus bicolor) North-ern Cardinal (Cardinalis cardinalis) and Orchard Oriole (Icterus spurius) showed significant increases duringspring migration fall sampling indicated that Carolina Wren Tufted Titmouse Black-throated Blue Warbler(Dendroica caerulescens) and Northern Cardinal had significantly higher capture rates Of 37 species includedin the migration monitoring data but not reliably represented by Breeding Bird Survey (BBS) data in any of thenortheastern physiographic strata 23 (62) showed significant declines at Manomet during at least one of thetwo migration periods There were significant correlations in percent changes in migrant capture rates betweenfall and spring BBS trends reported from the southern New England and northern New England physiographicstrata were correlated with changes in migrant capture rates However there were also inconsistencies betweenresults obtained by the two monitoring approaches suggesting that factors in addition to actual changes inbreeding populations may be reflected in the migration capture data Received 8 July 2003 accepted 26 March2004
Monitoring passerine population changesthrough counts collected along migratoryroutes has been attempted often (Hussell1981 Gauthreaux 1992 Hagan et al 1992Hussell et al 1992 Peach et al 1998 Ballardet al 2003) despite a variety of issues thatsometimes make the results of such studiesdifficult to interpret In particular detectingtrue changes in breeding populations may beconfounded by weather effects that produce
1 Manomet Center for Conservation Sciences POBox 1770 Manomet MA 02345 USA
2 Current address Conservation Biology ProgramDept of Environmental Studies Antioch New EnglandGraduate School 40 Avon St Keene NH 03431USA
dramatic differences among years in the num-bers of a particular species that appears duringmigration at a specific site (Gauthreaux 1971Moore and Simons 1992 Dunn and Hussell1995) while lsquolsquofalloutsrsquorsquo may provide excitingbirding conditions they also underscore thesubstantial stochastic element associated withany migration monitoring scheme Habitatchanges at a migration site also may causeapparent shifts in speciesrsquo abundances that areunrelated to true population levels (Remsenand Good 1996) Furthermore the specificbreeding populations actually represented bysamples of migrants are almost always un-known (Dunn and Hussell 1995) and con-ceivably may vary from year-to-year at a par-ticular migration site under the influence ofdiffering weather conditions Thus there is lit-
2 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tle doubt as some have pointed out (Butcheret al 1993 Sauer 1993 Remsen and Good1996) that monitoring changes in breedingpopulations through counts of migrants ob-tained by mist-net captures is risky business
Still most long-term field observers willquickly counter that something is happeningto the numbers of migrating land birds in east-ern North America (Robbins et al 1989 Ter-borgh 1989 Askins et al 1990) and that theseperceived changes are not easily discountedsimply by the effects of weather variations orlocal habitat change In fact although short-term fluctuations in numbers of migrants re-corded at a site may be completely meaning-less we contend that studies of longer dura-tionmdashdespite their inherent complicationsmdashmay yet help to elucidate true populationchanges simply by virtue of their long-termperspective
In this paper we present results to date ofone of North Americarsquos longest migrationmonitoring efforts conducted at ManometCenter for Conservation Sciences (formerlyManomet Bird Observatory MBO) from thelate 1960s to the present A preliminary anal-ysis of some of these data was presented byHagan et al (1992) herein we extend thescope of this earlier work in terms of yearsseasons and species included For 78 speciesin fall and 72 species in spring we examinefor the 32-year period 1970ndash2001 (a) changesin the numbers of individuals captured atManometrsquos banding station in coastal Massa-chusetts and (b) similarities in patterns of an-nual fluctuations of capture rates among spe-cies We also compare changes in capturerates with estimates of population trends ob-tained through a very different type of moni-toring study the North American BreedingBird Survey (BBS) which also has operatedover this extensive time period (Robbins et al1986 Sauer 1993 Sauer et al 2001)
METHODS
Manomet Center for Conservation Scienc-es located on the western side of Cape CodBay Plymouth County Massachusetts (418509 N 708 309 W) is characterized by brushysecond-growth deciduous woodland borderedon the east and south by a steep erodingcoastal bluff and on the west and north bybrushy wetlands Dominant tree species on the
7-ha plot include black cherry (Prunus sero-tina) shadbush (Amelanchier sp) red maple(Acer rubrum) white oak (Quercus alba) andpitch pine (Pinus rigida) Common catbrier(Smilax rotundifolia) bayberry (Myrica pen-sylvanica) staghorn sumac (Rhus typhina)honeysuckle (Lonicera morrowi) arrowwood(Viburnum recognitum) and poison ivy (Tox-icodendron radicans) are principal understoryspecies
Habitat succession was for the most partunchecked during the study period but thesitersquos location on an exposed coastal bluff re-sulted in annual natural lsquolsquopruningrsquorsquo by harshwinter storms that probably reduced the de-gree of change in habitat structure over timeSmall fields and grassland borders within thestudy site are mowed routinely Historic pho-tos of the area indicate that during the early1920s most of the study area consisted ofopen sheep pastures but by the time bandingoperations were begun in 1966 the site hadalready acquired the brushy second-growthcondition that characterizes it today An in-dividual black cherry tree was photographedin 1966 with a bander for height comparisonin a net lane about 10 m inland from the oceanbluff By 2003 the tree had grown an esti-mated 25 in height probably typical for theexposed coastal net lanes
From 45 to 50 nylon mist nets (12 m long26 m high 4 panels 36 mm extended mesh)were operated annually from 1970 to 2001inclusive because of less complete coverageand imprecise records regarding capture effortexpended during the first 4 years of the ob-servatoryrsquos existence (1966ndash1969) we ex-cluded these years from analysis Nets werekept at fixed locations throughout the studyOpening and closing times of nets were re-corded and used for calculating daily captureeffort (Robbins 1968) except for closuresduring adverse weather conditions generallynets were operated from 05 hr prior to sunriseto 05 hr after sunset Thus 50 nets open for12 hr equals 600 net hr Sampling was con-ducted 5ndash7 days per week during spring (15Aprilndash15 June) and fall (15 Augustndash15 No-vember) migration
During the study period 205454 individ-uals of 159 species were banded Recordsused in this analysis were selected from theoverall database using criteria described be-
3Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
low Only passerines are considered here sci-entific names and abbreviation codes for spe-cies referenced in the text are provided in theAppendix Willow and Alder flycatchers werecombined as were Bicknellrsquos and Gray-cheeked thrushes Palm Warbler races weretreated separately as lsquolsquoYellowrsquorsquo and lsquolsquoWest-ernrsquorsquo Palm warblers Captures of hybridlsquolsquoBrewsterrsquosrsquorsquo (n 5 3) and lsquolsquoLawrencersquosrsquorsquo (n 52) warblers were counted as Blue-wingedWarblers Repeat captures were eliminatedLocally breeding birds identified on the basisof well-developed brood patches or cloacalprotuberances were eliminated as werespring captures of hatching-year (HY) individ-uals Species that were captured by season infewer than 15 of the 32 years were eliminat-ed
For each species by season migration win-dows were calculated as falling between the1st and 99th percentiles of all capture datesacross all years any records outside thesewindows were excluded These cutoff valuesare provided in the Appendix For exampleduring fall migration 98 of all captures ofAmerican Redstarts occurred from 17 Augustto 12 October Any banding activity that tookplace within this window was considered torepresent a legitimate sampling day for thisspecies days that yielded no redstart capturesbut on which nets were open contributed avalue of zero to the overall calculation of cap-ture rate Any redstart captures that occurredbefore 17 August or after 12 October wereexcluded
For each species (by year and season) wecalculated a mean capture rate weighted bythe number of hours of mist netting that oc-curred on each contributing date That is incalculating mean seasonal and annual capturerates for a species the rate obtained on a daywhen nets were open for 400 net hr was givenmore emphasis than a rate obtained on a daywhen only 10 net hr of sampling took placeWe used Wilcoxon 2-sample tests to examinelong-term trends by testing (for each speciesby season) the hypothesis that mean capturerates were equal between Early (1970ndash1985)and Late (1986ndash2001) years of the study
Spearman rank correlations were used toassess concordance between each speciesrsquo falland spring capture rates and between the per-cent change in mean capture rates (Early ver-
sus Late) for each species and the populationtrends provided by BBS data (Sauer et al2001) These authors commendably cautionedthat lsquolsquoSmall sample sizes low relative abun-dance on survey routes imprecise trends andmissing data all can compromise BBS resultsOften users do not take these problems intoaccount when viewing BBS results and usethe results inappropriatelyrsquorsquo When we refer toBBS trends in this paper we conservativelyinclude only instances where the BBS lsquolsquoRe-gional Credibility Measurersquorsquo was in the best-sampled lsquolsquobluersquorsquo category That is BBStrends considered by Sauer et al (2001) toinclude lsquolsquoimportant deficienciesrsquorsquo (red) andlsquolsquodeficienciesrsquorsquo (yellow) were not used in thecorrelation analyses
Presentation of graphs showing changes incapture rates for each species and season com-bination in this study would require 150 in-dividual figures Although obviously beyondthe space limitations of this publication theseresults are provided online at wwwmanometorg Here in order to visually sum-marize major patterns of variation within thislarge set of data we calculated 3-year movingaverages based on annual mean capture ratesthen standardized each of these values as apercent of the maximum rate encountered foreach species among all years (by season)Next we used Wardrsquos minimum variance clus-tering approach as implemented by JMP sta-tistical software (SAS Institute Inc 2001) toidentify for each season an arbitrary sixgroups of species that exhibited similar year-to-year fluctuations in capture rates Finallywe plotted means and standard errors calcu-lated from the moving averages for speciesbelonging to each of these clusters
RESULTS
Of 72 species captured during spring mi-gration 60 (83) had lower mean capturerates during 1986ndash2001 than during 1970ndash1985 (Table 1) These declines were signifi-cant (P 005) in 36 species Twelve speciesshowed higher capture rates during 1986ndash2001 than during 1970ndash1985 in four of these(Carolina Wren Tufted Titmouse NorthernCardinal and Orchard Oriole) the increasesfrom Early to Late sampling periods were sig-nificant (P 001)
During fall migration 69 of 78 species
4 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
TABLE 1 Mean capture rates and percent change between Early (1970ndash1985) and Late (1986ndash2001) sam-pling periods during spring and fall migrations Population trend data from Breeding Bird Survey (BBS) pre-sented for comparison
Species
Spring capture ratea
Early Late ( change)
Fall capture ratea
Early Late ( change)
BBSb
SH nNE sNE
Eastern Wood-Pewee
0766 0464 (239) 0183 0141 (223) D D d
Yellow-belliedFlycatcher
1539 1336 (213) 0455 0297 (235) [i] I
Acadian Fly-catcher
0234 0206 (212) [d]
WillowAlder Fly-catcher
3269 3730 (14) 0754 0557 (226) [i] I [I]
Least Flycatcher 0844 0674 (220) 0866 0328 (262) D D DEastern Phoebe 0210 0200 (25) 0531 0574 (8) [I] [i] [i]Great Crested Fly-
catcher0535 0813 (52) D I D
Eastern Kingbird 0342 0280 (218) 0477 0108 (277) D d DWhite-eyed Vireo 0360 0155 (257) 0143 0092 (236) [I]Blue-headed Vireo 0313 0265 (215) 0461 0610 (32) I I [i]Warbling Vireo 0131 0074 (244) [i] I iPhiladelphia Vireo 0379 0208 (245) [i] [i]Red-eyed Vireo 1316 0783 (240) 4317 2834 (234) I [d] [d]Blue Jay 7071 2767 (261) 2326 1289 (245) [i] i DBlack-capped
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
1
THE WILSON BULLETINA QUARTERLY JOURNAL OF ORNITHOLOGY
Published by the Wilson Ornithological Society
VOL 116 NO 1 PAGES 1ndash118March 2004
Wilson Bulletin 116(1) 2004 pp 1ndash16
32 YEARS OF CHANGES IN PASSERINE NUMBERSDURING SPRING AND FALL MIGRATIONS
IN COASTAL MASSACHUSETTS
TREVOR L LLOYD-EVANS13 AND JONATHAN L ATWOOD12
ABSTRACTmdashUsing standardized mist-net captures collected over a 32-year period (1970ndash2001) we ex-amined changes in the capture rates of passerines recorded in coastal Massachusetts during fall (78 species) andspring (72 species) migration Capture rates of 45 species of fall migrants (58) declined significantly betweenearly (1970ndash1985) and late (1986ndash2001) years of the study 36 species of spring migrants (50) showed sig-nificant declines Only Carolina Wren (Thryothorus ludovicianus) Tufted Titmouse (Baeolophus bicolor) North-ern Cardinal (Cardinalis cardinalis) and Orchard Oriole (Icterus spurius) showed significant increases duringspring migration fall sampling indicated that Carolina Wren Tufted Titmouse Black-throated Blue Warbler(Dendroica caerulescens) and Northern Cardinal had significantly higher capture rates Of 37 species includedin the migration monitoring data but not reliably represented by Breeding Bird Survey (BBS) data in any of thenortheastern physiographic strata 23 (62) showed significant declines at Manomet during at least one of thetwo migration periods There were significant correlations in percent changes in migrant capture rates betweenfall and spring BBS trends reported from the southern New England and northern New England physiographicstrata were correlated with changes in migrant capture rates However there were also inconsistencies betweenresults obtained by the two monitoring approaches suggesting that factors in addition to actual changes inbreeding populations may be reflected in the migration capture data Received 8 July 2003 accepted 26 March2004
Monitoring passerine population changesthrough counts collected along migratoryroutes has been attempted often (Hussell1981 Gauthreaux 1992 Hagan et al 1992Hussell et al 1992 Peach et al 1998 Ballardet al 2003) despite a variety of issues thatsometimes make the results of such studiesdifficult to interpret In particular detectingtrue changes in breeding populations may beconfounded by weather effects that produce
1 Manomet Center for Conservation Sciences POBox 1770 Manomet MA 02345 USA
2 Current address Conservation Biology ProgramDept of Environmental Studies Antioch New EnglandGraduate School 40 Avon St Keene NH 03431USA
dramatic differences among years in the num-bers of a particular species that appears duringmigration at a specific site (Gauthreaux 1971Moore and Simons 1992 Dunn and Hussell1995) while lsquolsquofalloutsrsquorsquo may provide excitingbirding conditions they also underscore thesubstantial stochastic element associated withany migration monitoring scheme Habitatchanges at a migration site also may causeapparent shifts in speciesrsquo abundances that areunrelated to true population levels (Remsenand Good 1996) Furthermore the specificbreeding populations actually represented bysamples of migrants are almost always un-known (Dunn and Hussell 1995) and con-ceivably may vary from year-to-year at a par-ticular migration site under the influence ofdiffering weather conditions Thus there is lit-
2 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tle doubt as some have pointed out (Butcheret al 1993 Sauer 1993 Remsen and Good1996) that monitoring changes in breedingpopulations through counts of migrants ob-tained by mist-net captures is risky business
Still most long-term field observers willquickly counter that something is happeningto the numbers of migrating land birds in east-ern North America (Robbins et al 1989 Ter-borgh 1989 Askins et al 1990) and that theseperceived changes are not easily discountedsimply by the effects of weather variations orlocal habitat change In fact although short-term fluctuations in numbers of migrants re-corded at a site may be completely meaning-less we contend that studies of longer dura-tionmdashdespite their inherent complicationsmdashmay yet help to elucidate true populationchanges simply by virtue of their long-termperspective
In this paper we present results to date ofone of North Americarsquos longest migrationmonitoring efforts conducted at ManometCenter for Conservation Sciences (formerlyManomet Bird Observatory MBO) from thelate 1960s to the present A preliminary anal-ysis of some of these data was presented byHagan et al (1992) herein we extend thescope of this earlier work in terms of yearsseasons and species included For 78 speciesin fall and 72 species in spring we examinefor the 32-year period 1970ndash2001 (a) changesin the numbers of individuals captured atManometrsquos banding station in coastal Massa-chusetts and (b) similarities in patterns of an-nual fluctuations of capture rates among spe-cies We also compare changes in capturerates with estimates of population trends ob-tained through a very different type of moni-toring study the North American BreedingBird Survey (BBS) which also has operatedover this extensive time period (Robbins et al1986 Sauer 1993 Sauer et al 2001)
METHODS
Manomet Center for Conservation Scienc-es located on the western side of Cape CodBay Plymouth County Massachusetts (418509 N 708 309 W) is characterized by brushysecond-growth deciduous woodland borderedon the east and south by a steep erodingcoastal bluff and on the west and north bybrushy wetlands Dominant tree species on the
7-ha plot include black cherry (Prunus sero-tina) shadbush (Amelanchier sp) red maple(Acer rubrum) white oak (Quercus alba) andpitch pine (Pinus rigida) Common catbrier(Smilax rotundifolia) bayberry (Myrica pen-sylvanica) staghorn sumac (Rhus typhina)honeysuckle (Lonicera morrowi) arrowwood(Viburnum recognitum) and poison ivy (Tox-icodendron radicans) are principal understoryspecies
Habitat succession was for the most partunchecked during the study period but thesitersquos location on an exposed coastal bluff re-sulted in annual natural lsquolsquopruningrsquorsquo by harshwinter storms that probably reduced the de-gree of change in habitat structure over timeSmall fields and grassland borders within thestudy site are mowed routinely Historic pho-tos of the area indicate that during the early1920s most of the study area consisted ofopen sheep pastures but by the time bandingoperations were begun in 1966 the site hadalready acquired the brushy second-growthcondition that characterizes it today An in-dividual black cherry tree was photographedin 1966 with a bander for height comparisonin a net lane about 10 m inland from the oceanbluff By 2003 the tree had grown an esti-mated 25 in height probably typical for theexposed coastal net lanes
From 45 to 50 nylon mist nets (12 m long26 m high 4 panels 36 mm extended mesh)were operated annually from 1970 to 2001inclusive because of less complete coverageand imprecise records regarding capture effortexpended during the first 4 years of the ob-servatoryrsquos existence (1966ndash1969) we ex-cluded these years from analysis Nets werekept at fixed locations throughout the studyOpening and closing times of nets were re-corded and used for calculating daily captureeffort (Robbins 1968) except for closuresduring adverse weather conditions generallynets were operated from 05 hr prior to sunriseto 05 hr after sunset Thus 50 nets open for12 hr equals 600 net hr Sampling was con-ducted 5ndash7 days per week during spring (15Aprilndash15 June) and fall (15 Augustndash15 No-vember) migration
During the study period 205454 individ-uals of 159 species were banded Recordsused in this analysis were selected from theoverall database using criteria described be-
3Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
low Only passerines are considered here sci-entific names and abbreviation codes for spe-cies referenced in the text are provided in theAppendix Willow and Alder flycatchers werecombined as were Bicknellrsquos and Gray-cheeked thrushes Palm Warbler races weretreated separately as lsquolsquoYellowrsquorsquo and lsquolsquoWest-ernrsquorsquo Palm warblers Captures of hybridlsquolsquoBrewsterrsquosrsquorsquo (n 5 3) and lsquolsquoLawrencersquosrsquorsquo (n 52) warblers were counted as Blue-wingedWarblers Repeat captures were eliminatedLocally breeding birds identified on the basisof well-developed brood patches or cloacalprotuberances were eliminated as werespring captures of hatching-year (HY) individ-uals Species that were captured by season infewer than 15 of the 32 years were eliminat-ed
For each species by season migration win-dows were calculated as falling between the1st and 99th percentiles of all capture datesacross all years any records outside thesewindows were excluded These cutoff valuesare provided in the Appendix For exampleduring fall migration 98 of all captures ofAmerican Redstarts occurred from 17 Augustto 12 October Any banding activity that tookplace within this window was considered torepresent a legitimate sampling day for thisspecies days that yielded no redstart capturesbut on which nets were open contributed avalue of zero to the overall calculation of cap-ture rate Any redstart captures that occurredbefore 17 August or after 12 October wereexcluded
For each species (by year and season) wecalculated a mean capture rate weighted bythe number of hours of mist netting that oc-curred on each contributing date That is incalculating mean seasonal and annual capturerates for a species the rate obtained on a daywhen nets were open for 400 net hr was givenmore emphasis than a rate obtained on a daywhen only 10 net hr of sampling took placeWe used Wilcoxon 2-sample tests to examinelong-term trends by testing (for each speciesby season) the hypothesis that mean capturerates were equal between Early (1970ndash1985)and Late (1986ndash2001) years of the study
Spearman rank correlations were used toassess concordance between each speciesrsquo falland spring capture rates and between the per-cent change in mean capture rates (Early ver-
sus Late) for each species and the populationtrends provided by BBS data (Sauer et al2001) These authors commendably cautionedthat lsquolsquoSmall sample sizes low relative abun-dance on survey routes imprecise trends andmissing data all can compromise BBS resultsOften users do not take these problems intoaccount when viewing BBS results and usethe results inappropriatelyrsquorsquo When we refer toBBS trends in this paper we conservativelyinclude only instances where the BBS lsquolsquoRe-gional Credibility Measurersquorsquo was in the best-sampled lsquolsquobluersquorsquo category That is BBStrends considered by Sauer et al (2001) toinclude lsquolsquoimportant deficienciesrsquorsquo (red) andlsquolsquodeficienciesrsquorsquo (yellow) were not used in thecorrelation analyses
Presentation of graphs showing changes incapture rates for each species and season com-bination in this study would require 150 in-dividual figures Although obviously beyondthe space limitations of this publication theseresults are provided online at wwwmanometorg Here in order to visually sum-marize major patterns of variation within thislarge set of data we calculated 3-year movingaverages based on annual mean capture ratesthen standardized each of these values as apercent of the maximum rate encountered foreach species among all years (by season)Next we used Wardrsquos minimum variance clus-tering approach as implemented by JMP sta-tistical software (SAS Institute Inc 2001) toidentify for each season an arbitrary sixgroups of species that exhibited similar year-to-year fluctuations in capture rates Finallywe plotted means and standard errors calcu-lated from the moving averages for speciesbelonging to each of these clusters
RESULTS
Of 72 species captured during spring mi-gration 60 (83) had lower mean capturerates during 1986ndash2001 than during 1970ndash1985 (Table 1) These declines were signifi-cant (P 005) in 36 species Twelve speciesshowed higher capture rates during 1986ndash2001 than during 1970ndash1985 in four of these(Carolina Wren Tufted Titmouse NorthernCardinal and Orchard Oriole) the increasesfrom Early to Late sampling periods were sig-nificant (P 001)
During fall migration 69 of 78 species
4 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
TABLE 1 Mean capture rates and percent change between Early (1970ndash1985) and Late (1986ndash2001) sam-pling periods during spring and fall migrations Population trend data from Breeding Bird Survey (BBS) pre-sented for comparison
Species
Spring capture ratea
Early Late ( change)
Fall capture ratea
Early Late ( change)
BBSb
SH nNE sNE
Eastern Wood-Pewee
0766 0464 (239) 0183 0141 (223) D D d
Yellow-belliedFlycatcher
1539 1336 (213) 0455 0297 (235) [i] I
Acadian Fly-catcher
0234 0206 (212) [d]
WillowAlder Fly-catcher
3269 3730 (14) 0754 0557 (226) [i] I [I]
Least Flycatcher 0844 0674 (220) 0866 0328 (262) D D DEastern Phoebe 0210 0200 (25) 0531 0574 (8) [I] [i] [i]Great Crested Fly-
catcher0535 0813 (52) D I D
Eastern Kingbird 0342 0280 (218) 0477 0108 (277) D d DWhite-eyed Vireo 0360 0155 (257) 0143 0092 (236) [I]Blue-headed Vireo 0313 0265 (215) 0461 0610 (32) I I [i]Warbling Vireo 0131 0074 (244) [i] I iPhiladelphia Vireo 0379 0208 (245) [i] [i]Red-eyed Vireo 1316 0783 (240) 4317 2834 (234) I [d] [d]Blue Jay 7071 2767 (261) 2326 1289 (245) [i] i DBlack-capped
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
2 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tle doubt as some have pointed out (Butcheret al 1993 Sauer 1993 Remsen and Good1996) that monitoring changes in breedingpopulations through counts of migrants ob-tained by mist-net captures is risky business
Still most long-term field observers willquickly counter that something is happeningto the numbers of migrating land birds in east-ern North America (Robbins et al 1989 Ter-borgh 1989 Askins et al 1990) and that theseperceived changes are not easily discountedsimply by the effects of weather variations orlocal habitat change In fact although short-term fluctuations in numbers of migrants re-corded at a site may be completely meaning-less we contend that studies of longer dura-tionmdashdespite their inherent complicationsmdashmay yet help to elucidate true populationchanges simply by virtue of their long-termperspective
In this paper we present results to date ofone of North Americarsquos longest migrationmonitoring efforts conducted at ManometCenter for Conservation Sciences (formerlyManomet Bird Observatory MBO) from thelate 1960s to the present A preliminary anal-ysis of some of these data was presented byHagan et al (1992) herein we extend thescope of this earlier work in terms of yearsseasons and species included For 78 speciesin fall and 72 species in spring we examinefor the 32-year period 1970ndash2001 (a) changesin the numbers of individuals captured atManometrsquos banding station in coastal Massa-chusetts and (b) similarities in patterns of an-nual fluctuations of capture rates among spe-cies We also compare changes in capturerates with estimates of population trends ob-tained through a very different type of moni-toring study the North American BreedingBird Survey (BBS) which also has operatedover this extensive time period (Robbins et al1986 Sauer 1993 Sauer et al 2001)
METHODS
Manomet Center for Conservation Scienc-es located on the western side of Cape CodBay Plymouth County Massachusetts (418509 N 708 309 W) is characterized by brushysecond-growth deciduous woodland borderedon the east and south by a steep erodingcoastal bluff and on the west and north bybrushy wetlands Dominant tree species on the
7-ha plot include black cherry (Prunus sero-tina) shadbush (Amelanchier sp) red maple(Acer rubrum) white oak (Quercus alba) andpitch pine (Pinus rigida) Common catbrier(Smilax rotundifolia) bayberry (Myrica pen-sylvanica) staghorn sumac (Rhus typhina)honeysuckle (Lonicera morrowi) arrowwood(Viburnum recognitum) and poison ivy (Tox-icodendron radicans) are principal understoryspecies
Habitat succession was for the most partunchecked during the study period but thesitersquos location on an exposed coastal bluff re-sulted in annual natural lsquolsquopruningrsquorsquo by harshwinter storms that probably reduced the de-gree of change in habitat structure over timeSmall fields and grassland borders within thestudy site are mowed routinely Historic pho-tos of the area indicate that during the early1920s most of the study area consisted ofopen sheep pastures but by the time bandingoperations were begun in 1966 the site hadalready acquired the brushy second-growthcondition that characterizes it today An in-dividual black cherry tree was photographedin 1966 with a bander for height comparisonin a net lane about 10 m inland from the oceanbluff By 2003 the tree had grown an esti-mated 25 in height probably typical for theexposed coastal net lanes
From 45 to 50 nylon mist nets (12 m long26 m high 4 panels 36 mm extended mesh)were operated annually from 1970 to 2001inclusive because of less complete coverageand imprecise records regarding capture effortexpended during the first 4 years of the ob-servatoryrsquos existence (1966ndash1969) we ex-cluded these years from analysis Nets werekept at fixed locations throughout the studyOpening and closing times of nets were re-corded and used for calculating daily captureeffort (Robbins 1968) except for closuresduring adverse weather conditions generallynets were operated from 05 hr prior to sunriseto 05 hr after sunset Thus 50 nets open for12 hr equals 600 net hr Sampling was con-ducted 5ndash7 days per week during spring (15Aprilndash15 June) and fall (15 Augustndash15 No-vember) migration
During the study period 205454 individ-uals of 159 species were banded Recordsused in this analysis were selected from theoverall database using criteria described be-
3Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
low Only passerines are considered here sci-entific names and abbreviation codes for spe-cies referenced in the text are provided in theAppendix Willow and Alder flycatchers werecombined as were Bicknellrsquos and Gray-cheeked thrushes Palm Warbler races weretreated separately as lsquolsquoYellowrsquorsquo and lsquolsquoWest-ernrsquorsquo Palm warblers Captures of hybridlsquolsquoBrewsterrsquosrsquorsquo (n 5 3) and lsquolsquoLawrencersquosrsquorsquo (n 52) warblers were counted as Blue-wingedWarblers Repeat captures were eliminatedLocally breeding birds identified on the basisof well-developed brood patches or cloacalprotuberances were eliminated as werespring captures of hatching-year (HY) individ-uals Species that were captured by season infewer than 15 of the 32 years were eliminat-ed
For each species by season migration win-dows were calculated as falling between the1st and 99th percentiles of all capture datesacross all years any records outside thesewindows were excluded These cutoff valuesare provided in the Appendix For exampleduring fall migration 98 of all captures ofAmerican Redstarts occurred from 17 Augustto 12 October Any banding activity that tookplace within this window was considered torepresent a legitimate sampling day for thisspecies days that yielded no redstart capturesbut on which nets were open contributed avalue of zero to the overall calculation of cap-ture rate Any redstart captures that occurredbefore 17 August or after 12 October wereexcluded
For each species (by year and season) wecalculated a mean capture rate weighted bythe number of hours of mist netting that oc-curred on each contributing date That is incalculating mean seasonal and annual capturerates for a species the rate obtained on a daywhen nets were open for 400 net hr was givenmore emphasis than a rate obtained on a daywhen only 10 net hr of sampling took placeWe used Wilcoxon 2-sample tests to examinelong-term trends by testing (for each speciesby season) the hypothesis that mean capturerates were equal between Early (1970ndash1985)and Late (1986ndash2001) years of the study
Spearman rank correlations were used toassess concordance between each speciesrsquo falland spring capture rates and between the per-cent change in mean capture rates (Early ver-
sus Late) for each species and the populationtrends provided by BBS data (Sauer et al2001) These authors commendably cautionedthat lsquolsquoSmall sample sizes low relative abun-dance on survey routes imprecise trends andmissing data all can compromise BBS resultsOften users do not take these problems intoaccount when viewing BBS results and usethe results inappropriatelyrsquorsquo When we refer toBBS trends in this paper we conservativelyinclude only instances where the BBS lsquolsquoRe-gional Credibility Measurersquorsquo was in the best-sampled lsquolsquobluersquorsquo category That is BBStrends considered by Sauer et al (2001) toinclude lsquolsquoimportant deficienciesrsquorsquo (red) andlsquolsquodeficienciesrsquorsquo (yellow) were not used in thecorrelation analyses
Presentation of graphs showing changes incapture rates for each species and season com-bination in this study would require 150 in-dividual figures Although obviously beyondthe space limitations of this publication theseresults are provided online at wwwmanometorg Here in order to visually sum-marize major patterns of variation within thislarge set of data we calculated 3-year movingaverages based on annual mean capture ratesthen standardized each of these values as apercent of the maximum rate encountered foreach species among all years (by season)Next we used Wardrsquos minimum variance clus-tering approach as implemented by JMP sta-tistical software (SAS Institute Inc 2001) toidentify for each season an arbitrary sixgroups of species that exhibited similar year-to-year fluctuations in capture rates Finallywe plotted means and standard errors calcu-lated from the moving averages for speciesbelonging to each of these clusters
RESULTS
Of 72 species captured during spring mi-gration 60 (83) had lower mean capturerates during 1986ndash2001 than during 1970ndash1985 (Table 1) These declines were signifi-cant (P 005) in 36 species Twelve speciesshowed higher capture rates during 1986ndash2001 than during 1970ndash1985 in four of these(Carolina Wren Tufted Titmouse NorthernCardinal and Orchard Oriole) the increasesfrom Early to Late sampling periods were sig-nificant (P 001)
During fall migration 69 of 78 species
4 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
TABLE 1 Mean capture rates and percent change between Early (1970ndash1985) and Late (1986ndash2001) sam-pling periods during spring and fall migrations Population trend data from Breeding Bird Survey (BBS) pre-sented for comparison
Species
Spring capture ratea
Early Late ( change)
Fall capture ratea
Early Late ( change)
BBSb
SH nNE sNE
Eastern Wood-Pewee
0766 0464 (239) 0183 0141 (223) D D d
Yellow-belliedFlycatcher
1539 1336 (213) 0455 0297 (235) [i] I
Acadian Fly-catcher
0234 0206 (212) [d]
WillowAlder Fly-catcher
3269 3730 (14) 0754 0557 (226) [i] I [I]
Least Flycatcher 0844 0674 (220) 0866 0328 (262) D D DEastern Phoebe 0210 0200 (25) 0531 0574 (8) [I] [i] [i]Great Crested Fly-
catcher0535 0813 (52) D I D
Eastern Kingbird 0342 0280 (218) 0477 0108 (277) D d DWhite-eyed Vireo 0360 0155 (257) 0143 0092 (236) [I]Blue-headed Vireo 0313 0265 (215) 0461 0610 (32) I I [i]Warbling Vireo 0131 0074 (244) [i] I iPhiladelphia Vireo 0379 0208 (245) [i] [i]Red-eyed Vireo 1316 0783 (240) 4317 2834 (234) I [d] [d]Blue Jay 7071 2767 (261) 2326 1289 (245) [i] i DBlack-capped
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
3Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
low Only passerines are considered here sci-entific names and abbreviation codes for spe-cies referenced in the text are provided in theAppendix Willow and Alder flycatchers werecombined as were Bicknellrsquos and Gray-cheeked thrushes Palm Warbler races weretreated separately as lsquolsquoYellowrsquorsquo and lsquolsquoWest-ernrsquorsquo Palm warblers Captures of hybridlsquolsquoBrewsterrsquosrsquorsquo (n 5 3) and lsquolsquoLawrencersquosrsquorsquo (n 52) warblers were counted as Blue-wingedWarblers Repeat captures were eliminatedLocally breeding birds identified on the basisof well-developed brood patches or cloacalprotuberances were eliminated as werespring captures of hatching-year (HY) individ-uals Species that were captured by season infewer than 15 of the 32 years were eliminat-ed
For each species by season migration win-dows were calculated as falling between the1st and 99th percentiles of all capture datesacross all years any records outside thesewindows were excluded These cutoff valuesare provided in the Appendix For exampleduring fall migration 98 of all captures ofAmerican Redstarts occurred from 17 Augustto 12 October Any banding activity that tookplace within this window was considered torepresent a legitimate sampling day for thisspecies days that yielded no redstart capturesbut on which nets were open contributed avalue of zero to the overall calculation of cap-ture rate Any redstart captures that occurredbefore 17 August or after 12 October wereexcluded
For each species (by year and season) wecalculated a mean capture rate weighted bythe number of hours of mist netting that oc-curred on each contributing date That is incalculating mean seasonal and annual capturerates for a species the rate obtained on a daywhen nets were open for 400 net hr was givenmore emphasis than a rate obtained on a daywhen only 10 net hr of sampling took placeWe used Wilcoxon 2-sample tests to examinelong-term trends by testing (for each speciesby season) the hypothesis that mean capturerates were equal between Early (1970ndash1985)and Late (1986ndash2001) years of the study
Spearman rank correlations were used toassess concordance between each speciesrsquo falland spring capture rates and between the per-cent change in mean capture rates (Early ver-
sus Late) for each species and the populationtrends provided by BBS data (Sauer et al2001) These authors commendably cautionedthat lsquolsquoSmall sample sizes low relative abun-dance on survey routes imprecise trends andmissing data all can compromise BBS resultsOften users do not take these problems intoaccount when viewing BBS results and usethe results inappropriatelyrsquorsquo When we refer toBBS trends in this paper we conservativelyinclude only instances where the BBS lsquolsquoRe-gional Credibility Measurersquorsquo was in the best-sampled lsquolsquobluersquorsquo category That is BBStrends considered by Sauer et al (2001) toinclude lsquolsquoimportant deficienciesrsquorsquo (red) andlsquolsquodeficienciesrsquorsquo (yellow) were not used in thecorrelation analyses
Presentation of graphs showing changes incapture rates for each species and season com-bination in this study would require 150 in-dividual figures Although obviously beyondthe space limitations of this publication theseresults are provided online at wwwmanometorg Here in order to visually sum-marize major patterns of variation within thislarge set of data we calculated 3-year movingaverages based on annual mean capture ratesthen standardized each of these values as apercent of the maximum rate encountered foreach species among all years (by season)Next we used Wardrsquos minimum variance clus-tering approach as implemented by JMP sta-tistical software (SAS Institute Inc 2001) toidentify for each season an arbitrary sixgroups of species that exhibited similar year-to-year fluctuations in capture rates Finallywe plotted means and standard errors calcu-lated from the moving averages for speciesbelonging to each of these clusters
RESULTS
Of 72 species captured during spring mi-gration 60 (83) had lower mean capturerates during 1986ndash2001 than during 1970ndash1985 (Table 1) These declines were signifi-cant (P 005) in 36 species Twelve speciesshowed higher capture rates during 1986ndash2001 than during 1970ndash1985 in four of these(Carolina Wren Tufted Titmouse NorthernCardinal and Orchard Oriole) the increasesfrom Early to Late sampling periods were sig-nificant (P 001)
During fall migration 69 of 78 species
4 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
TABLE 1 Mean capture rates and percent change between Early (1970ndash1985) and Late (1986ndash2001) sam-pling periods during spring and fall migrations Population trend data from Breeding Bird Survey (BBS) pre-sented for comparison
Species
Spring capture ratea
Early Late ( change)
Fall capture ratea
Early Late ( change)
BBSb
SH nNE sNE
Eastern Wood-Pewee
0766 0464 (239) 0183 0141 (223) D D d
Yellow-belliedFlycatcher
1539 1336 (213) 0455 0297 (235) [i] I
Acadian Fly-catcher
0234 0206 (212) [d]
WillowAlder Fly-catcher
3269 3730 (14) 0754 0557 (226) [i] I [I]
Least Flycatcher 0844 0674 (220) 0866 0328 (262) D D DEastern Phoebe 0210 0200 (25) 0531 0574 (8) [I] [i] [i]Great Crested Fly-
catcher0535 0813 (52) D I D
Eastern Kingbird 0342 0280 (218) 0477 0108 (277) D d DWhite-eyed Vireo 0360 0155 (257) 0143 0092 (236) [I]Blue-headed Vireo 0313 0265 (215) 0461 0610 (32) I I [i]Warbling Vireo 0131 0074 (244) [i] I iPhiladelphia Vireo 0379 0208 (245) [i] [i]Red-eyed Vireo 1316 0783 (240) 4317 2834 (234) I [d] [d]Blue Jay 7071 2767 (261) 2326 1289 (245) [i] i DBlack-capped
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
4 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
TABLE 1 Mean capture rates and percent change between Early (1970ndash1985) and Late (1986ndash2001) sam-pling periods during spring and fall migrations Population trend data from Breeding Bird Survey (BBS) pre-sented for comparison
Species
Spring capture ratea
Early Late ( change)
Fall capture ratea
Early Late ( change)
BBSb
SH nNE sNE
Eastern Wood-Pewee
0766 0464 (239) 0183 0141 (223) D D d
Yellow-belliedFlycatcher
1539 1336 (213) 0455 0297 (235) [i] I
Acadian Fly-catcher
0234 0206 (212) [d]
WillowAlder Fly-catcher
3269 3730 (14) 0754 0557 (226) [i] I [I]
Least Flycatcher 0844 0674 (220) 0866 0328 (262) D D DEastern Phoebe 0210 0200 (25) 0531 0574 (8) [I] [i] [i]Great Crested Fly-
catcher0535 0813 (52) D I D
Eastern Kingbird 0342 0280 (218) 0477 0108 (277) D d DWhite-eyed Vireo 0360 0155 (257) 0143 0092 (236) [I]Blue-headed Vireo 0313 0265 (215) 0461 0610 (32) I I [i]Warbling Vireo 0131 0074 (244) [i] I iPhiladelphia Vireo 0379 0208 (245) [i] [i]Red-eyed Vireo 1316 0783 (240) 4317 2834 (234) I [d] [d]Blue Jay 7071 2767 (261) 2326 1289 (245) [i] i DBlack-capped
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
a Based on weighted means of capture rates by year and season (n 5 16 in both Early and Late periods) Change 5 (Late 2 Early)Early 3 100Significant differences between mean Early and Late capture rates (Wilcoxon 2-sample test) indicated by asterisks P 005 P 001 P 0001
b Based on Sauer et al (2001) analysis of 1966ndash2000 BBS data from physiographic strata 28 (SH eastern Spruce-Hardwoods) 27 (nNE northern NewEngland) and 12 (sNE southern New England) D 5 significant (P 005) decline d 5 non-significant (P $ 005) decline I 5 significant increase i5 non-significant increase nc 5 no change Symbols in brackets [ ] indicate that Sauer et al (2001) considered these trend estimates unreliable due tolsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo in sampling Blanks indicate physiographic regions where a given species was not represented in BBS trenddata
FIG 1 Correlations between spring and fall mi-gration periods for percent change in capture rates be-tween Early and Late periods of the study (P 0001n 5 63 species) Three apparent outliers (CARW Car-olina Wren ETTI Tufted Titmouse and NOCANorthern Cardinal) shown as solid circles
(88) had lower capture rates during Lateyears of the study than during Early years (Ta-ble 1) these differences were significant (P 005) in 45 species Nine species had highercapture rates during 1986ndash2001 than during
1970ndash1985 in four of these (Carolina WrenTufted Titmouse Black-throated Blue War-bler and Northern Cardinal) the differenceswere significant (P 005)
Percent changes in mean capture rates fromEarly to Late years of the study were posi-tively correlated between spring and fall mi-grations (Rho 5 055 P 0001 n 5 63 spe-cies Fig 1) Exclusion of three outliers (Car-olina Wren Tufted Titmouse and NorthernCardinal) that showed dramatic increases incapture rates during both migration periodsdid not substantially alter the strength of theobserved correlation (Rho 5 048 P 0001n 5 60 species) There were no species thatshowed significant increases in capture rateduring one season and significant decreases inthe other
Because of uncertainty regarding the loca-tion of breeding populations represented bymigrants in coastal Massachusetts we com-pared our results with BBS trends from threephysiographic regions (southern New Eng-land northern New England and easternSprucendashHardwoods) that we considered themost likely sources of the majority of mi-grants observed at Manomet (Fig 2) Capturesof spring migrants were significantly (P
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
7Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 2 Location of Manomet Center for Conser-vation Sciences (MBO) study site relative to threenortheastern physiographic strata used in analysis ofBreeding Bird Survey data
TABLE 2 Correlations between percent change inmean capture rates (Early versus Late sampling peri-ods) and Breeding Bird Survey trends (Sauer et al2001) from three physiographic regions BBS resultswith lsquolsquodeficienciesrsquorsquo or lsquolsquoimportant deficienciesrsquorsquo havebeen excluded from analysis (see text)
Physiographic regiona
sNE nNE SH
Spring
Fall
036 (0087)b
n 5 23050 (0018)
n 5 22
045 (0011)n 5 31
047 (0006)n 5 33
017 (0402)n 5 26
034 (0087)n 5 26
a sNE 5 southern New England nNE 5 northern New England SH 5eastern Spruce-Hardwoods
b Spearman rank correlation (P-value)
005) and positively correlated with BBStrends from northern New England duringfall migration we found significant positivecorrelations between capture rates and BBStrends from both southern and northern NewEngland physiographic strata (Table 2)
Four species that breed at high latitudes orhigh elevations [Gray-cheekedBicknellrsquosThrush Palm Warbler (western) AmericanTree Sparrow and White-crowned Sparrow]were represented in the migration monitoringdata but not by BBS analyses all of these spe-cies showed significantly declining capturerates (P 005) between Early and Late pe-riods of the study Thirty-three species repre-sented in the migration monitoring data wereconsidered by Sauer et al (2001) to be rep-resented unreliably by BBS data in any of thenortheastern physiographic strata (Table 1) 19of these species (Philadelphia Vireo BrownCreeper House Wren Blue-gray GnatcatcherSwainsonrsquos Thrush Northern MockingbirdTennessee Warbler Northern Parula CapeMay Warbler Bay-breasted Warbler Black-poll Warbler Northern Waterthrush MourningWarbler Wilsonrsquos Warbler Yellow-breastedChat Savannah Sparrow Fox Sparrow Rose-breasted Grosbeak and Baltimore Oriole)showed significant declines at Manomet dur-ing at least one of the two migration periods
while capture rates of 3 (Tufted TitmouseCarolina Wren and Orchard Oriole) signifi-cantly increased during fall and spring migra-tions (Table 1)
Apparent inconsistencies between trendsbased on migration captures at Manomet andBBS data were greatest for the easternSprucendashHardwoods stratum and least for thesouthern New England stratum This patternwas true during both spring (Fig 3) and fall(Fig 4) migration periods Spring migrationcaptures indicated significant (P 005) de-clines in three species for which BBS analysesfound significant increases Red-eyed Vireo(eastern SprucendashHardwoods) Ovenbird(northern New England) and Gray Catbird(southern New England) Fall migration cap-tures significantly declined in four specieswhereas BBS analyses showed significant in-creases Red-eyed Vireo and Yellow-rumped(Myrtle) Warbler (eastern SprucendashHard-woods) Yellow-bellied Flycatcher and Yel-low-rumped (Myrtle) Warbler (northern NewEngland) and Gray Catbird (southern NewEngland)
For each migration period cluster analysiswas used to identify an arbitrary six groups ofspecies that shared general patterns of changein capture rates across years (Figs 5 and 6)This approach allowed us to summarize trenddata visually for a large number of speciesHowever we note that similarities in capturerates among members of a group do not nec-essarily mean that shared trends were causedby similar proximate factors In some casescluster membership may in fact reflect theinfluence of shared ecology For example
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
8 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 3 Comparison of trends in capture rate basedon spring migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in(A) spruce-hardwoods (B) northern New England and(C) southern New England physiographic strata lsquolsquoDE-CLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005lsquolsquoINCREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $005 For example of 13 species showing significantdeclines according to BBS data from southern NewEngland 70 showed significant declines in Manometcapture rates and 20 showed declines in Manometcapture rates that were not statistically significant
FIG 4 Comparison of trends in capture rate basedon fall migration monitoring at Manomet relative totrends derived from BBS data (Sauer et al 2001) in (A)spruce-hardwoods (B) northern New England and (C)southern New England physiographic strata lsquolsquoDECLINE-significantrsquorsquo P 005 lsquolsquoDeclinersquorsquo P $ 005 lsquolsquoIN-CREASE-significantrsquorsquo P 005 lsquolsquoIncreasersquorsquo P $ 005
capture rates of Blackpoll Warbler NorthernParula Tennessee Warbler Cape May War-bler Blackburnian Warbler and Bay-breastedWarbler peaked during the mid to late 1970s
(Fig 6F) many if not all of these specieslikely responded to a widespread outbreak ofspruce budworm (Choristoneura fumerifanaClem) in eastern North America during thistime period (Hagan et al 1992) CarolinaWren and Northern Cardinal two speciesknown to have shown dramatic regional pop-ulation increases during the last decades (Ha-
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
9Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 5 Major patterns of change in spring capture rates of 72 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
gan et al 1992) were grouped together duringboth spring (Fig 5E) and fall (Fig 6C) mi-grations
We speculate that at least some of the clus-tering results (and therefore underlying trendpatterns) may reflect local weather conditionsthat would have influenced capture rates ofspecies with similar migration periods Therewere significant differences among mean mi-gration dates for each of the six clusters (Fig7 Wilcoxon rank sum test spring x2 5 1934df 5 5 P 5 0002 fall x2 5 1612 df 5 5P 5 0007) During spring most species as-signed to clusters A and D (Fig 5A D) wererelatively early migrants with mean migrationdates of 7 May (SE 5 45 days) and 3 May(SE 5 34 days) respectively both of thesegroups showed somewhat elevated capturerates during the mid to late 1980s possibly
suggesting that during several years in thistime period weather conditions caused larger-than-normal numbers of these species to bepresent in coastal Massachusetts Similarlymost species assigned to fall cluster A (Fig6A) were relatively late migrants with a meanmigration date of 9 October (SE 5 33 days)the relatively high capture rates that charac-terized this group during the early 1970s mayhave reflected local weather conditions thataffected any species with a peak migration pe-riod in early October
Nonetheless we hesitate to try and providefurther explanations for the species lsquolsquomember-shipsrsquorsquo in each of these groupings Instead weprefer to emphasize a more general perspec-tive noting that only one of the six trend plotsfrom each migration period (spring Fig 5Efall Fig 6C) showed obvious increases in
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
10 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
FIG 6 Major patterns of change in fall capture rates of 78 species in coastal Massachusetts 1970ndash2001Error bars represent 6 1 SE Species contributing to each plot are indicated with four-letter banding codes seeAppendix
capture rates Four of the plots from each mi-gration period (spring Fig 5BndashD F fall Fig6AndashB EndashF) showed decreasing trends in cap-ture rates One plot from each migration pe-riod was characterized by peak capture ratesduring the early to mid 1980s with compa-rably low rates before and after this time pe-riod (spring Fig 5A fall Fig 6D)
DISCUSSION
The Breeding Bird Survey is widely rec-ognized as a primary source of informationregarding conservation priorities for NorthAmerican birds (Geissler and Noon 1981Butcher et al 1993 Smith et al 1993 Jameset al 1996 Carter et al 2000) yet relativelyfew studies have attempted to validate its con-clusions via independent alternative monitor-ing schemes Hussell et al (1992) compared
a migration index from 1961 to 1988 at LongPoint Ontario with BBS trends in that prov-ince and obtained positive correlations as didFrancis and Hussell (1998) in Ontario Othermultiple-year comparisons with BBS datahave included intensive counts in Quebec(Jobin et al 1996) and migration monitoringat Southeast Farallon Island California (Pyleet al 1994) and at Point Reyes California(Ballard et al 2003) In this paper we presentresults from a long-term study based on stan-dardized mist-net capture efforts during falland spring migrations in coastal Massachu-setts and compare these data with estimatesof population trends obtained by Sauer et al(2001) in their analysis of BBS data
At first glance it would appear that there isgood agreement between our results and BBSanalyses There were strong correlations be-
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
11Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
FIG 7 Mean migration dates during spring andfall for clusters derived from capture trends Clusterletters correspond with those shown in Fig 5 (spring)and Fig 6 (fall) Error bars represent 6 1 SE
tween population trends observed in each ofthe three BBS strata considered here andchanges in Manomet capture rates between1970ndash1985 and 1986ndash2001 suggesting thatboth methods do in fact reflect changes inregional breeding populations For exampleLeast Flycatcher was the only species to de-cline significantly in all three northeasternBBS strata and it showed a significant declinein capture rate during fall at Manomet Of 10species for which significant declines werenoted in two of three northeastern BBS stratawe found significant declines in capture ratesduring at least one of the two migration sea-sons for 7 (Eastern Kingbird Wood ThrushCommon Yellowthroat Eastern Towhee FieldSparrow White-throated Sparrow and PurpleFinch) 2 of the other species (Eastern Wood-Pewee and Common Grackle) declined non-significantly at Manomet while Great CrestedFlycatcher showed a non-significant increasebased on migration data Of 23 species forwhich the BBS showed significant populationdeclines in at least one of the three physio-graphic strata considered here 18 (78) alsoshowed significant declines in capture ratesduring spring andor fall migration
Yet the situation is more complex than thesecomparisons might suggest In many cases ourstudy failed to detect increasing populationtrends indicated by the BBS Of 16 speciesshown by Sauer et al (2001) to have had sig-nificant increases in at least one of the phys-iographic strata considered here we found sig-nificantly increased capture rates in only 1(Northern Cardinal) Furthermore we observedsignificant declines in capture rates duringspring andor fall migration for five speciesfound by the BBS to be exhibiting significantpopulation increases in at least one of the threephysiographic strata [Yellow-bellied Flycatch-er Red-eyed Vireo Gray Catbird Yellow-rum-ped (Myrtle) Warbler and Ovenbird]
In our study we found significantly declin-ing capture rates during one or both migrationperiods in 54 of 87 species (62) but only 5species (6) showed significant increasesAmong the 37 of these species for which re-liable BBS results were available from at leastone of the northeastrsquos physiographic strataSauer et al (2001) found significant declinesin 22 cases (59) and significant increases in15 (41) Great Crested Flycatcher and GrayCatbird showed opposite significant trends indifferent physiographic strata These contrastssuggest that factors in addition to changes inbreeding populations may be confounding therelationship with capture rates observed dur-ing migration
We especially note that the patterns we de-scribe here could have emerged if captures ofmost species we sampled during migrationwere somehow being reduced over time byfactors unrelated to actual changes in breedingpopulations For example long-term changesin climate conceivably could cause shifts inregional weather patterns that in turn mightsystematically affect the number of migrantsappearing in coastal Massachusetts (Moore etal 1993) However we are not aware of anyevidence of long-term increases in migrationcaptures at established banding operations eastof the Mississippi that might be expected ifactual migration patterns were changing Oras the vegetation at Manomet has maturedsince 1970 some species of migrants maynow move through the study area at heightswhere they simply avoid making contact withthe nets (26 m in height) (Remsen and Good1996) species that would continue to be ac-
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
12 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
tive primarily within 3 m of the ground evenin the presence of higher canopy cover mightbe avoiding the site because of its generallymore forested aspect (Moore et al 1993)
Conversely the BBS results may them-selves be subject to error due to the effects ofroadside bias (Temple and Wiens 1989 Kellerand Fuller 1995) or short count period (Welsh1995 Jobin et al 1996) thus the trend esti-mates by Sauer et al (2001) may not neces-sarily provide a lsquolsquogold standardrsquorsquo by which tovalidate Manometrsquos migration count results Itis also quite possible that a species could beincreasing in one BBS stratum and decreasingin another or showing conflicting trends with-in different regions of a single stratummdashanyof which could confuse the relationship be-tween trends shown by the BBS and migrationmonitoring data sets One of the three BBSstrata considered here the eastern Spruce-Hardwood forest is so large (353538 km2Rosenberg and Hodgman 2000) that presen-tation of a single trend to represent this entirearea seems fraught with uncertainty at leastequal to our lack of knowledge about the de-tailed breeding locations of migrants passingthrough Manomet
At this point we have no way of furtherassessing these possible explanations Certain-ly capture rates of migrants at Manomet dur-ing spring and fall have in many caseschanged substantially from 1970 to 2001 andthe vast majority of these changes have beendeclines Migration count data from otherstudies also indicate long-term declines inNew England birds for example Hill and Ha-gan (1991) found that spring surveys of 26Neotropical migrants in Middlesex and Essexcounties of Massachusetts declined on aver-age nearly 1 per year from 1954 to 1987Personal comments from several banders fa-miliar with the location for 301 years all in-dicate that there are fewer birds in recent yearsat Manomet and in New England generally
Many of the declines documented at Man-omet coincide with declines in breeding pop-ulations reported by the most reliable BBSdata Nonetheless there are some apparent in-consistencies between results of the two anal-yses that we cannot explain It appears likelythat a combination of factors have influencedthe number of migrants captured at Manometsince 1970 We believe however that the pre-
ponderance of data suggests long-term popu-lation declines in a wide variety of both Neo-tropical and shorter-distance migrants thatgreatly exceed the few increases that havebeen observed
ACKNOWLEDGMENTS
It is impossible for us to name all of the contributorsto this project many of whom have given their timefaithfully since the late 1960s Hosts of students andvolunteers have foregone sleep and decent salaries inorder to spend their days walking net lanes The trust-ees and friends of Manomet Center for ConservationSciences made this work possible through unfailingpersonal and financial assistance We deeply appreciatethe support that all of you have given from CranberryHill to Stage Point your enthusiasm and dedicationwill always endure Thank you C J Ralph C S Rob-bins and an anonymous reviewer provided helpfulcomments on a preliminary draft of the manuscriptWe dedicate this paper to K Anderson and those initialbanders whose vision and passion gave birth to Man-omet Bird Observatory
LITERATURE CITED
ASKINS R A J F LYNCH AND R GREENBERG 1990Population declines in migratory birds in easternNorth America Current Ornithology 71ndash57
BALLARD G G R GEUPEL N NUR AND T GARDALI2003 Long-term declines and decadel patterns inpopulation trends of songbirds in western NorthAmerica 1979ndash1999 Condor 105737ndash755
BUTCHER G S B PETERJOHN AND C J RALPH 1993Overview of national bird population monitoringprograms and databases Pages 192ndash203 in Statusand management of Neotropical migratory birds(D M Finch and P W Stangel Eds) GeneralTechnical Report RM-229 US Forest ServiceRocky Mountain Forest and Range ExperimentStation Fort Collins Colorado
CARTER M F W C HUNTER D N PASHLEY AND KV ROSENBERG 2000 Setting conservation priori-ties for landbirds in the United States the Partnersin Flight approach Auk 177541ndash548
DUNN E H AND D J T HUSSELL 1995 Using mi-gration counts to monitor landbird populations re-view and evaluation of current status Current Or-nithology 1243ndash48
FRANCIS C M AND D J T HUSSELL 1998 Changesin numbers of landbirds counted in migration atLong Point Bird Observatory 1961ndash1997 BirdPopulations 437ndash66
GAUTHREAUX S A JR 1971 A radar and direct visualstudy of passerine spring migration in southernLouisiana Auk 88343ndash365
GAUTHREAUX S A JR 1992 The use of weather radarto monitor long-term patterns of trans-Gulf migra-tion in spring Pages 96ndash100 in Ecology and con-servation of Neotropical migrant landbirds (J M
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
13Lloyd-Evans and Atwood bull 32 YEARS OF PASSERINE MIGRATION COUNTS
Hagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
GEISSLER P H AND B R NOON 1981 Estimates ofavian population trends from the North AmericanBreeding Bird Survey Studies in Avian Biology642ndash51
HAGAN J M T L LLOYD-EVANS J L ATWOOD AND
D S WOOD 1992 Long-term changes in migra-tory landbirds in the northeastern United Statesevidence from migration capture data Pages 115ndash130 in Ecology and conservation of Neotropicalmigrant landbirds (J M Hagan III and D WJohnson Eds) Smithsonian Institution PressWashington DC
HILL N P AND J M HAGAN III 1991 Populationtrends of some northeastern North American land-birds a half-century of data Wilson Bulletin 103165ndash182
HUSSELL D J T 1981 The use of migration countsfor monitoring bird population levels Studies inAvian Biology 692ndash102
HUSSELL D J T M H MATHER AND P H SINCLAIR1992 Trends in numbers of tropical- and temper-atendashwintering migrant landbirds in migration atLong Point Ontario 1961ndash1988 Pages 101ndash114in Ecology and conservation of Neotropical mi-grant landbirds (J M Hagan III and D W John-son Eds) Smithsonian Institution Press Wash-ington DC
JAMES F C C E MCCULLOCH AND D A WIEDENFELD1996 New approaches to the analysis of populationtrends in land birds Ecology 7713ndash27
JOBIN B J-L DESGRANGES AND C BOUTIN 1996Comparison of BBS and intensive surveys at se-lected BBS stops Bird Populations 314ndash25
KELLER C M E AND M R FULLER 1995 Compar-ison of birds detected from roadside and off-roadpoint counts in the Shenandoah National ParkPages 111ndash116 in Monitoring bird populations bypoint counts (C J Ralph J R Sauer and S Droe-ge Eds) General Technical Report PSW-149US Forest Service Pacific Southwest ResearchStation Albany California
MOORE F R S A GAUTHREAUX JR P KERLINGERAND T R SIMONS 1993 Stopover habitat man-agement implications and guidelines Pages 58ndash69 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
MOORE F R AND T R SIMONS 1992 Habitat suit-ability and stopover ecology of Neotropical land-bird migrants Pages 345ndash355 in Ecology and con-servation of Neotropical migrant landbirds (J MHagan III and D W Johnson Eds) SmithsonianInstitution Press Washington DC
PEACH W J S R BAILLIE AND D E BALMER 1998Long-term changes in the abundance of passerines
in Britain and Ireland as measured by constanteffort mist-netting Bird Study 45257ndash275
PYLE P N NUR AND D F DESANTE 1994 Trends innocturnal migrant landbird populations at South-east Farallon Island California 1968ndash1992 Stud-ies in Avian Biology 1558ndash74
REMSEN J V JR AND D A GOOD 1996 Misuse ofdata from mist-net captures to assess relativeabundance in bird populations Auk 113381ndash398
ROBBINS C S 1968 Net hours a common denomi-nator for the study of bird populations EasternBird-Banding Association News 3131ndash35
ROBBINS C S D BYSTRAK AND P H GEISSLER 1986The Breeding Bird Survey its first fifteen years1965ndash1979 US Fish and Wildlife Service Re-search Publication 157 Washington DC
ROBBINS C S J R SAUER R S GREENBERG AND SDROEGE 1989 Population declines in NorthAmerican birds that migrate to the NeotropicsProceedings of the National Academy Sciences867658ndash7662
ROSENBERG K V AND T P HODGMAN 2000 Partnersin Flight bird conservation plan for easternspruce-hardwood forest (physiographic area 28)draft 10 Online at httpwwwblmgovwildlifeplanplp28p10pdf (accessed 5 May 2003)
SAS INSTITUTE INC 2001 JMP Start Statistics 2nd edDuxburyndashThomson Learning Pacific Grove Cal-ifornia
SAUER J R 1993 Monitoring goals and programs ofthe US Fish and Wildlife Service Pages 245ndash251 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
SAUER J R J E HINES AND J FALLON 2001 TheNorth American Breeding Bird Survey resultsand analysis 1966ndash2000 ver 20012 USGS Pa-tuxent Wildlife Research Center Laurel Mary-land Online at httpwwwmbr-pwrcusgsgovbbsbbshtml (accessed 24 June 2001)
SMITH C R D M PENCE AND R J OrsquoCONNOR 1993Status of Neotropical migratory birds in theNortheast a preliminary assessment Pages 172ndash188 in Status and management of Neotropical mi-gratory birds (D M Finch and P W StangelEds) General Technical Report RM-229 USForest Service Rocky Mountain Forest and RangeExperiment Station Fort Collins Colorado
TEMPLE S A AND J A WIENS 1989 Bird populationsand environmental changes can birds be bio-in-dicators American Birds 43260ndash270
TERBORGH J 1989 Where have all the birds gonePrinceton University Press Princeton New Jersey
WELSH D A 1995 An overview of the Ontario ForestBird Monitoring Program in Canada Pages 93ndash97 in Monitoring bird populations by point counts(C J Ralph J R Sauer and S Droege Eds)General Technical Report PSW-149 US ForestService Pacific Southwest Research Station Al-bany California
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
birdAgelaius phoeniceus 11 May (18 Aprndash12 Jun) mdash
COGR Common Grackle Quiscalus quiscula 09 May (18 Aprndash13 Jun) mdashBHCO Brown-headed Cow-
birdMolothrus ater 03 May (15 Aprndash13 Jun) mdash
OROR Orchard Oriole Icterus spurius 18 May (10 Mayndash03 Jun) mdashBAOR Baltimore Oriole Icterus galbula 20 May (09 Mayndash14 Jun) 28 Aug (15 Augndash09 Oct)PUFI Purple Finch Carpodacus purpu-
reusmdash 03 Oct (21 Augndash05 Nov)
HOFI House Finch Carpodacus mexi-canus
08 May (15 Aprndash14 Jun) 12 Sep (16 Augndash16 Nov)
AMGO American Goldfinch Carduelis tristis 19 May (18 Aprndash15 Jun) 25 Oct (20 Augndash15 Nov)
14 THE WILSON BULLETIN bull Vol 116 No 1 March 2004
APPENDIX Banding codes scientific names and migration periods of species referred to in text Foreach season the limits of sampling window (1st and 99th percentiles) are given in parentheses following themean date of migration (all years combined) Dashes (mdash) indicate species-season combinations (such as fallAcadian Flycatcher) that failed to meet analysis criteria described in Methods
