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1002 SHORT COMMUNICATIONSThe Condor 99:1002-10040 The Cooper Omlthological Society 1997

MAXIMUM DIVE DEPTH S OF THE PERUVIAN DIVING-PETREL

CARLOS B. ZAVALAGAAv. Guardia Chalaca 1333, Callao, Peru,

e-mail: czav@telematic.edu.peJAIME JAHNCKE~

Institute de1 Mar de1 Peru (IMARPE), Apartado 22, Callao, Peru,e-mail: jjahnck@net.cosapidata.com.pe

Abstract. The mean maximum dive depth attainedfor 22 adult Peruvian Diving-petrels (Pelecanoidesgarnotii) was 31.6 + 3.6 m. The deepestdive was 83.1m. This maximu m dive depth was 81% deeper thanthat predicted by its body size (46 m ) and the deepestreported for a seabird weighing less than 2 10 g.

Key words: Peruvian Diving-petrels, divingdepths, foraging behavior, Pelecanoidesgamotii.The max imum dive depth of several axa of free-livingseabirdshas been successfullydetermined using cap-illary-tube gauge s. Although these devices provideonly the record of the deepest dives, which norm allyrepresent less frequent exploratory d ives beyo nd theanima ls n orma l foraging depths Lishm an and Croxall1983. Piatt and Nettleshio 1985. Watanu ki et al. 1996).they are useful in that they provide an initial insightinto an anima ls underw ater capabilities, habitat use,and access o deep prey (Adam s and Brown 1983, Hax-ris et al. 1990. Prince and Jones 1992). Maximumdepth gaugesare light-weight and representat presentthe only viable an d reliable technique to meas ure thediving capabilities of small birds such as diving-pet-rels, which are incapable of carrying heavy a nd moresophisticateddevices.The Peruvian Diving-petrel (Pelecunoides garnotii),the largestof the four extant diving-petrels, s endem icto the cold nutrient-rich Peruvian Coastal Current(Murphy 1936). Once ab undant, hese birds have beenadversely affected by hunting , fishing activities, andreduction of nesting habitat (Murphy 1936, Hays1989). Although Peruvian Diving-petrels are consid-ered endangered Wege and Long 1995), informationabou t the breeding and foraging ecology of thesebirdsis scarce. The maximum breeding population in Peruwas estimated to be 13,000 pairs in 1996, whereastheir distribution was restricted to o nly two islands ncentral Peru: La Vieja and S an Gallan (Jahncke andGoya, u npubl. data).In this study we report maximu m dive dep ths at-tained by breeding Peruvian Diving-petrels and com-pare them w ith data obtained from other wing-pro-pelled divers.

Received 15 April 1997. Accepted 30 July 1997.* C urrent address:Apartado 18-0807, Lima 18, Peru.

METHODSThe field wo rk was carried out on La Vieja Island,Peru (1416S, 76llW) from August 199 5 to May1996 . The island lies at the entranceof IndependenciaBay, abo ut 50 km south of the ParacasPeninsula.Depth gauges were deployed on 66 adult birds atdifferent s tagesof the breeding cycle (incu bation andchick rearing). Adults were captured n their burrows,weighed, meas ured,and ringed. Gaugeswere attachedto feathers n the center of the birds back using quick-set epoxy glue (Devco n 5-minu te epoxy). The deviceswere retrieved after l-3 days.Capillary-tube dep th gauges, similar to those de-scribed by Burge r and Wilson ( 1988 ), consistedof a 6cm length of flexible, clear PVC tubing (internal di-ameter of 0.8 mm ), coated n ternally with a thin layerof indicator powd er (one part methylene blue:threeparts talcum pow der). Once coated, the tub e was heat-sealed at o ne end. Each tub e weighed approximately0.5 g, which was < 0.25% of adult body weight (X =202 g, n = 65), and had a cross-sectional rea of lessthan 1 0 mm 2, about 0.7% of the maximum cross-sec-tional area of an adult bird (X = 14.6 cm2, n = 32).During diving, w ater enters the tube by hyd rostaticpressure,compressing he volume of air inside the lu-men. The volume of compressedair varies inversely

*L0Maximum Depth (m)

FIGURE 1. Maximum d ive depths of Peruvian Div-ing-petrels (n = 22) b reeding in La Vieja Island, Peru,between August 1994 and May 1995.

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TAB LE 1. Max imum diving depths recorded for three species of diving-petrels and two similar-sized alcids.D,, predicted was determined by the equation D,, = 75.905M -36 Burger 1991).

SpeciesDiving-petrels

Pelecanoides georgicusP. urinatrixP. garnotii

AlcidsPtychoramphus aleuticusAlle alle

Weight MClll Observed Predicted(9) D,, (ml %, Cm) D,, Cm)

93.0 25.7 48.6 35.8147.4 38.9 63.6 41.1202.0 31.6 83.1 45.6

190.0 - 43.0 44.9160.0 - 35.0 42.5

n Reference

6 Prince and Jones 1992103 Chaste1199422 This study23 Burger 1991- Burger 1991

with hydrostatic pressure (with increasing depth) asdescribed by Boyles Law. When the bird is at thesurface, the water w ashes out the powder, leaving aline at the point of ma ximum com pression.The max-imum depth attained was calculatedby the equation:D max lO.O8[(L&) - 11;

where D,, is the max imum depth in meters, 10.0 8 isthe height (m) of a co lumn of sea water equivalent to1 atmosphereof pressure,L, is the total length of thetube, and Ld is the length of the tube with un dissolvedindicator (Burger and Wilson 198 8). After recove ry ofthe recorders, he length of the tube with indicator wasmeasured o the nearest 0.1 mm using calipers. Tubeswith water droplets in the lumen were discarded.The accuracy of the depth gauges was checked bylowering nine of them into sea-w ater from the SNP-1Research Vessel of IM ARP E (Instituto de1 Mar de1Peru) to known depths ranging from 10 to 150 m.Means are expressed5 SE.RESULTSMaximum depth gaugesoverestimated eal depths byan average of 13.2% (2.2-35.0%) with shallowerdepths < 70 m) being recordedmore precisely (< 8%error) than deeper depths (> 70 m). Estimated depthscould be correctedby the equation:Real depth = 3.12+ 0.8 X estimateddepth, for estimateddepths angingfrom 10 to 150 m (+ = 0.99, n = 9).Forty-one gauges (62% ) were recovered after oneforaging trip, but only 22 gave readablemeasurements.Mean maximum dive depth was 31.6 ? 3.6 m, and91% of the maximum dives were between 10 and 50m (Fig. 1). The sha llowest dive was 10.0 m, a nd thedeepestdive was 83.1 m. T here was no significantdif-ference in the ma ximum d ive depth attained by birdsincubating eggs (n = 34.4 C 3.8 m, n = 5) and thoserearing chicks (x = 30.8 I 4.6 m, n = 17) (Mann-Whitney U = 28, P = 0.27).DISCUSSIONThe mean maximum dive depth attained by the Peru-vian Diving-petrel was similar to those reported forother species of diving-petrels (Table 1). H owever,when the deepestdive depths ecorded or each speciesare comp ared, values are related, among other things,to body size, as in other species of diving sea birds(Piatt and Nettleship 198 5, Burger 1 991).Burger (1991) determined that maximum dive

depths of penguins and alcids were positively corre-lated to body size and can be predictedby the equationD mar 75.905M03r6,where M = mass in kg, for bothgroups combined. Using this equation with the m eanweight of Peruvian Diving-petrels (202 g), a maximumdive of 45.8 m is expected. This v alue is about halfthat of the observed max imum dive of 83.1 m. L ike-wise, max imum depths attainedby the three speciesofdiving-petrels were deeper than those recorded forsimilar-sized alcids (Table l), which are recognized obe close ecological and morphological analogue sofdiving-petrels Thoresen 1969 ). This evidence suggeststhat Peruv ian Diving-petrels are capab le of exploringdeep waters and that diving c apabilitiesof diving-pet-rels may differ from those exhibited by other wing-propelled divers.Diving patterns of Peruvian Diving-petrels may bevariable-according to location, time of the year,-andbehavior of its prey (Wilson and Wilson 1990). Themajor prey speciesconsumedby thesebirds aroundLaVieja Islandduring the study period were small crus-taceans,mainly euphausiids 25.2% by mass) and lar-val stages of Peruvian anchovies (Engrazdis ringens)and other fishes (27.3% by mass) (Jahncke et al., un-publ. data). Euphausiidsare widespread to depths ofat least 300 m (Brinton 1962, cited in Santanderet al.1981), whereas Peruvian anchovy larvae are confinedto the upper 60 m (Sameoto 1981). Both prey typesshow die1 vertical m igration, remaining in deeper wa-ter s trata during the day and rising to the su rface bynight (Brinton 19 62, cited in San tander et al. 198 1,Sameoto 1981). Because Peruvian Diving-petrels aremainly diurnal foragers (Jahncke, unpub l. data), it isexpected hat these birds need to reach deep water stra-ta to catch food.

We thank Elisa Goya, Domenica Zileri, Raul San-chez, Cecilia Flores, and Marga ret Fraser or their helpwith the field work. David Duffy, Rory Wilson, IanStirling, Patricia Majluf, and two anonym ous eview-ers sugg ested improvemen ts to early drafts of thismanuscript.We are grateful to PESCA PERU for per-mission to work on the island and for providing ac-commodations.LITERATURE CITEDADAMS, N. J., AND C. R. BROWN. 1983. Diving depthsof the Gentoo Penguin (Pygoscelis Papua). Con-dor 85:503-504.

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BURGE R, . E. 1991. Maximum diving depths and un-derwater foraging in alcids and penguins. Can.Wildl. Serv., Occas. Pap. 68:9-15.BURGER, . E., AND R. P WUON . 1988. Capillary-tube depth gauges for diving animals: an assess-ment of their accu racy and applicability. J. FieldOmithol. 59:345-354.CHASTE L, . 1994. Maximum diving depths of Com-mon Diving Pe trelsPelecanoides urinatrix at Ker-guelen Islands. Polar Biol. 14:21 1-213 .HARRIS,M. P, H. TOWLL,A. E RUSSELL,ND S. WAN-LESS. 1990. Maximum dive depths attained byauks feeding young on the Isle of May, Scotland.Scottish Birds 16:25 -28.HAY S, C. 198 9. Th e Peruvian Diving-petrel in Peru.Oryx 23:102-105.LISHMAN,G. S., AND J. F CROXALL. 1983. Divingdepths of the C hinstrap Penguin, Pygoscelis ant-arcticu. Br. Antarct. Surv. Bull. 61:2 1-25.

MURPHY,R. C . 193 6. Oceanic birds of South Amer-ica. Vol. 2. Macmillan, New York.PIAT~,J. E, AND N. NETIZESHIP. 985. D iving depthsof four alcids. Auk 102:293-297.PRINCE, P A., AND M. JONES.1992. Maximum divedepthsattainedby South Georgia diving petrelPe-

Zecanoides georgicus at Bird Island, South Geor-gia. Antarct. Sci. 4:433-434 .SAMEOTO, . 1981. Distribution and abundan ce f sixspeciesof fish larvae in P eruvian waters and theirrelationship with the physical and biological en-vironment: Boletin Inst&uto de1 Mar de1 Peru.Volumen Extraordinario:164-170.SANTANDER,., G. LUYO,S. CARRA SCO,. V~LU, AND0. S. DE CASTILLO. 981. Catalog0 de zooplanc-ton en el mar peruano.Primera parte: area Pisco-San Jua n. Boletfn Instituto de1Mar de1Peru 6:1-75.THORESEN,. C. 196 9. Observationson the breedingbehaviourof the Diving P etrelPelecanoides u. ur-inatrix (Gmelin). Notomis 16:241-260.WATANUKI, ., A. KATO,AND Y. NAI~O. 1996 . Divingperformance of male a nd female JapaneseCor-morants. Can. J. Zool. 74: 1098-l 109:WECE D. C.. AND A. J. LONG. 1995. Kev areas forthreatenedbirds in the Neo tropics. BGdlife C on-servation Series No. 5. Smithson. Inst. Press,Washington,DC.WILSON,R. l?, AND M. T. Wnso~. 1990. Foragingecology of breedingSpheniscus penguins,p. 1 8 -206. In L. S. Davis and J. T Darby [eds.], Penguinbiology. Academ ic Press, San Diego.

The Condor 99:lOCb10070 The CooperOrnithological ociety 1997

DIVING DEPTHS OF TWO TROPICAL PELECANIFORMES: THE RED-TAILEDTROPICBTRD AND THE RED-FOOTED BOOBY

MAITHIEU LE CORRECEBC-CNRS Villiers en Bois-79360 Beauvoir sur Niort, France

Abstract. The diving ability of two tropical Pele-caniformes, the Red-footed Booby (Sulu sulu) and theRed-tailed Tropicbird (Phaethon rubricauda) wasstudiedon Europa sland, southernMozambique Chan-nel, using capillary depth recorders itted on breedingadults. Both speciesmainly exploited the first 4 m ofthe water c olumn. Although such a depth can bereached solely by passive plunge diving, the range ofdepths reached by the two species suggests hat theymay, at least sometimes, use their feet an d wings toperform active underwater pursuit swimming. Intra-specific com parisonof the depth reachedby Red -tailedTropicbirdsalso suggests hat this speciesmay changeits diving behavior seasonally.

Key words: diving depth, feeding ecology, Red-tailed Tropicbird, Red-footed Booby, Phaethon rubri-cauda, Sula sula, Europa Island.

1Received 8 M ay 1997. Accepted 31 J uly 199 7.

Most boobies (tropical Szdidae) and all tropicbirds(Phaethontidue) a pelagic plunge diving seabirds(Ashmole 1971, Nelson 1978, Schreiber and Clapp1987 ), foraging s olitarily (tropicbirds,Masked Booby)or collectively-(most boobies), and feeding mainly onflying fishes and squ id (Ashmole an d Ashmole 196 7,Diamond 1974, 1975, Harrison et al. 1983). Plungedivers supposedlyhave limited diving capacities, thedepth they reach dependingmainly on the momentumgained during the plunge (Ashmole 1971). However,at least Cape Gannets (S&I cupensis) can use theirwings and feet to gain additional depth (Adam s andWalter 199 3). Here I report diving performances oftwo tropical plunge divers, the Red-tailed Tropicbird(Phaethon rubricaudu, 0.8 kg) and the Red-footedBooby (Sula sula, 0.9 kg).METHODSThe study was conductedon Europ a Island (222OS,40 22 E) in the southe rnMozambique Channel. About3,00 0 p airs of Red-footed Boobies and about 3,500