26

INTRODUCTION

Satellite transmitters have provided the means for impres-sive studies detailing the migrations of certain large-bodied shorebirds (Driscoll & Ueta 2002, Gill et al. 2009, Watts et al. 2008). Similar tracking is impossible in many species of small to medium-sized shorebirds (including the Pacific Golden-Plover Pluvialis fulva), because the transmitters are too heavy for the birds to carry. Archival light level geolocators are an alternative to satellite tracking, and the recent advent of miniaturized loggers that smaller shorebirds (even songbirds, see Stutchbury et al. 2009, 2010) can transport over great distances has opened exciting new research opportunities for wader researchers (Clark et al. 2010). The first use of geolo-cators to study movements of a long-distance migrant shore-bird was by Conklin et al. (2010) and involved the tracking of Bar-tailed Godwits Limosa lapponica migrating between New Zealand and Alaska. This was followed by studies of two species similar in mass to Pacific Golden-Plovers: Ruddy Turnstones Arenaria interpres traveling between Australia and E Siberia (Minton et al. 2010), and Red Knots Calidris canutus migrating between South America and the Canadian Arctic (Niles et al. 2010).

In this paper, the first study of its kind on Pacific Golden-Plovers, we present new insight on the annual migratory cycle of birds wintering on Oahu Island, Hawaii. Our findings are from geolocators deployed in spring on pre-migrant territorial plovers, then recovered in fall when the birds returned to their previous winter territories. Since birds must be recaptured in order to download the data archived in their geolocators, the strong inter-season site-fidelity of Pacific Golden-Plovers on wintering grounds (see below) renders this species ideal for logger-based studies. The information obtainable from geolocators (migratory routes, duration of long-distance flights, stopover sites, and depending on where loggers are deployed, either breeding or wintering ground destinations) is clearly fundamental to understanding the biology of any migratory wader, and may be of critical importance from the conservation perspective.

METHODS

The geolocators used in this study (manufactured by Brit-ish Antarctic Survey) sampled ambient light level every minute and recorded the maximum during each 10 min period. They also measured potential contact with seawater

Johnson, O.W., Fielding, L., Fox, J.W., Gold, R.S., Goodwill, R.H. & Johnson, P.M. 2011. Tracking the migrations of Pacific Golden-Plovers (Pluvialis fulva) between Hawaii and Alaska: New insight on flight performance, breeding ground destinations, and nesting from birds carrying light level geolocators. Wader Study Group Bull. 118(1): 26–31.

Keywords: Pacific Golden-Plover, Pluvialis fulva, geolocator, data logger, migration, migratory pathways, ground speed, flight time, stopovers, wintering grounds, breeding grounds, nesting success

This study is the first in which light level geolocators (data loggers) were deployed on Pacific Golden-Plovers Pluvialis fulva. In spring 2009 and 2010, we logger-equipped a total of 24 plovers at wintering grounds on Oahu, Hawaii; 22 returned in the subsequent fall migrations, and of these 20 were recaptured. Almost all of the recovered geolocators had archived the full roundtrip to Alaska including nesting locations. Transpacific flights were nonstop along direct north–south pathways. On average, the northward passage required approximately 3 days and covered about 4,800 km; the southward around 4 days and 4,900 km. Ground speeds fluctuated widely during flights (almost certainly because of variable winds); mean ground speeds were estimated at 63 kph in spring, 58 kph in fall. The capacity of this plover for nonstop flight remains unknown; however our results indicate that it exceeds 5 days. All 20 birds nested in southerly parts of the Alaska breeding range, from the Yukon–Kuskokwim Delta to nearly the tip of the Alaska Peninsula, indicating major migratory connectivity between Hawaii and those regions. Geolocator archives during the time birds were on breeding grounds showed periods of successive days with erratic light level patterns (“noise”). Such noise seemed a clear indicator of nesting activities, and also of hatching success or failure.

Tracking the migrations of Pacific Golden-Plovers (Pluvialis fulva) between Hawaii and Alaska: New insight

on flight performance, breeding ground destinations, and nesting from birds carrying light level geolocators

Oscar W. Johnson 1, Lauren Fielding 2, James W. Fox 3, Roger S. Gold 2, Roger H. Goodwill 2 & Patricia M. Johnson 1

1 Department of Ecology, Montana State University, Bozeman, MT 59717, USA. owjohnson2105@aol.com2 Department of Biology, Brigham Young University – Hawaii, Laie, HI 96762, USA3 British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK

27Johnson et al.: Tracking of migrating Pacific Golden-Plovers between Hawaii and Alaska

every 3 seconds. Light level records indicated daily sunrise and sunset times from which latitudes and longitudes were determined. We deployed a total of 24 geolocators (12 in each of two seasons) at two wintering ground study sites on Oahu. The sample was comprised of 15 males and 9 females (sex determined from dimorphic breeding plumage, see Johnson & Connors 2010), all were territorial winter residents on lawns. The first 12 birds were captured over the period 28 Mar to 9 Apr 2009 and equipped with BAS MK-14 geolocators; birds in the second group were caught from 12 Mar to 2 Apr 2010, and BAS MK-10 geolocators (a smaller logger that replaced the MK-14) were attached to them. The 2009 group consisted of 11 plovers captured in Honolulu at the National Memorial Cemetery of the Pacific (21.3°N, 157.8°W) and one bird from the opposite side of the island on the BYU-Hawaii campus (21.6°N, 157.9°W); in 2010, the entire sample of 12 birds was caught at BYU-Hawaii.

We assembled logger/band units a week or more before affixing them to birds. Fabrication involved tying each geolo-cator to a Darvic band (12 mm in length) with un-waxed den-tal floss looped through two small holes drilled in the band, then bonding the logger to the band with marine epoxy. The finished composite weighed from 1.8 to 2.0 g (approximately 1.2% of average mass at migration, see Johnson & Connors 2010). When placed on the leg, the overlapping ends of the band were sealed with a small quantity of additional epoxy. Attachment to the bird was on the tibiotarsus proximal to a USGS metal band, the latter to prevent any possible slippage of the Darvic ring downward over the ankle (Fig. 1, also see Conklin & Battley 2010). A unique combination of color-bands allowing individual recognition of each bird was placed on the opposite tibiotarsus.

Almost all plovers carrying loggers returned to their previ-ous territories during the subsequent fall periods when they were recaptured, and their geolocators recovered. Birds were captured using one or the other of two techniques: with mist nets in the pre-dawn or with a “Super Talon” net-gun during daytime hours. The net-gun (see Advanced Weapons Sys-tems, www.lawenforcementmall.com) was especially useful for birds having territories adjacent to cemetery or campus roadways where they often were close enough to be netted from our vehicle as we were slowly driving by. Once a bird was in hand, the logger was removed by slicing through the band with a rotary Dremel tool equipped with a small cutting wheel. During this process, we placed a narrow metal shield between the band and the leg to prevent injury.

We edited and analyzed geolocator data with software (BasTrak) provided by British Antarctic Survey. The down-loaded information was processed using a fixed light thresh-old value (see Fox 2010). Erratic light transitions (due to shading events) were rejected. Post-editing, the remaining data were converted to locations using software within the BasTrak suite. This produced a cluster of points at each site where the plover had spent time during its annual cycle (i.e., stopovers, nesting location and winter territory). For nesting and stopover sites, we consolidated each cluster into a single point representing the approximate average location. Using Google Earth, we then plotted these points along with the 12-hour transpacific legs (as integrated from BasTrak output) of the individual’s migrations. The clustering of points around the winter territory of each bird (the site where it had been captured for geolocator deployment and then recaptured post-migration) was due to uncertainties inherent to light level geolocation, mostly uncontrollable shading variations caused by weather and foliage, plus artificial light which is a major variable on urban Hawaii wintering grounds. We made

no effort to consolidate territory-associated clusters as the lat/long of each territory was precisely known. Degrees of error are unavoidable when using geolocator technology to track the movements of birds, but longitude determination is invariably more accurate than latitude (Fox 2010, Phillips et al. 2004). Based on the latter sources together with the posi-tional errors estimated in other shorebird studies (±130 km, Bar-tailed Godwits, Conklin et al. 2010; ±300 km, Ruddy Turnstones, Minton et al. 2010; and ±150 km, Red Knots, Niles et al. 2010), we considered it reasonable to assume positional uncertainties in the present study of ±100 km for fixed locations (nesting locations and stopovers) and ±200 km for birds in flight. Notably, for very fast movements north or south, uncertainties may be greater than ±200 km due to the fragility of the astronomical algorithms used to calculate posi-tions from light levels. Aside from the foregoing applications of BasTrak, we also examined the daily graphic records gen-erated sequentially by that software (specifically those from the breeding grounds) for indications of nesting activities.

Using Google Earth, we estimated ground speed and flight-hours for each individual during the passage from landfall Oahu to landfall Alaska in spring, the reverse in fall. We first measured the distance (in km) between two widely spaced offshore points on each bird’s migratory track. The points chosen for this initial measurement were geolocations marking either the beginning or end of a 12-hour leg, thus the number of hours (i.e., the remaining legs) between the two points was known. Furthermore, the points were sepa-rated from landfalls in both Hawaii and Alaska by wide gaps averaging 628 km (well beyond the ±200 km margin of error mentioned above) so as to ensure that the track from one point to the other was totally that of the bird in flight. From these measures of distance and time, we calculated apparent ground speed (kph) for the offshore point-to-point portion of the flight. We then applied this ground speed to the complete track including the gaps and accordingly estimated the number of hours required for the entire landfall-to-landfall passage.

RESULTS

Initial responses of plovers to geolocators

Based on recent reports, it appears that shorebirds read-ily adapt to carrying geolocators (Conklin & Battley 2010, Conklin et al. 2010, Niles et al. 2010), and the same was true of Pacific Golden-Plovers. Nonetheless, it is useful to record how birds react to the somewhat bulky foreign object that has been attached to them, and to assess any possible undesirable effects (Clark et al. 2010, Niles et al. 2010). Following attach-ment of geolocators to the plovers, we released each bird at the site where it had been captured (i.e., either directly back into its territory or near its territory). Upon release, individu-als ran or flew varying distances and commenced vigorous preening. Typically, there were long bouts of preening that included considerable pecking at the newly deployed geolo-cator; overall this was similar to the behaviours that follow ordinary banding. A worrisome situation occurred early in the study when we watched newly logger-equipped plovers in flight and saw the leg carrying the geolocator drooping downward beneath the body as if injured. Fortunately, this anomaly (presumably caused by the bird being unaccustomed to the extra weight attached to one of its legs) was self-correcting, and within a day flight configuration was back to normal with both legs tucked up in the usual position. As the season progressed, we made frequent observations of logger-carrying birds until their spring departure. During this

28 Wader Study Group Bulletin 118(1) 2011

pre-migratory period we noted them occasionally pecking at their geolocators while preening, otherwise there was no apparent logger-related impairment as foraging, territorial behaviours, and flight appeared identical to birds not carrying loggers. Similar lack of negative effects in logger-equipped birds was reported in Bar-tailed Godwits (Conklin & Battley 2010) and Red Knots (Niles et al. 2010).

Survival of geolocator birds

Of the 24 individuals carrying geolocators, 22 returned (11 in each of the two subsequent fall migrations, overall 92% sur-vival) and reoccupied their former winter territories. Survival at this rate fell near the upper end of previously documented autumn returns (80–100%) among numerous cohorts of plovers banded on Oahu wintering grounds (Johnson et al. 1997, 2001a,b, 2004, OWJ unpubl. data). Clearly, carrying a logger on one leg and bands on the other during a roundtrip to Alaska caused no unusual mortality. We recaptured 20 of the 22 returnees and recovered their loggers. Of the two birds not recaptured, one individual had shed the geolocator (it had

fallen off the band), and the other disappeared from its territory (possibly depredated) before we were able to catch it. In no case among recaptured plovers was there any indication of abnormality on the leg that had carried the logger.

Migratory movements and nesting

Of the 20 geolocators recovered, 18 had functioned perfectly recording details of the entire migration between Oahu and Alaska including approximate nesting locations; one logger archived the spring passage to Alaska along with the bird’s nesting lo-cation, then stopped working; and the last gave us a reasonable fix on where the bird nested but no usable information concerning the migration itself. Thus, the findings described in the remainder of this section are based on archival data from 19 full northward tracks in spring, 20 nesting locations, and 18 full southward tracks in fall.

Spring departures from Oahu ranged from 18 April to 4 May with most (11 birds) during 24 to 28

April. While en route to nesting grounds, four plovers made stopovers of 2–19 days at approximately 57.5°N (three were on the Alaska Peninsula, one was farther east probably on Kodiak Island); the remaining 15 birds appeared to return di-rectly to breeding grounds. During stopovers, two individuals contacted seawater and two did not. The sample population nested in southerly parts of the species’ Alaskan breeding range, from approximately 61.8°N, 163.3°W on the Yukon–Kuskokwim Delta to approximately 55.8°N, 161.1°W on the Alaska Peninsula, and arrived at these sites over the period 22 Apr to 10 May (Fig. 2). We found no correlation between timing of departure from Oahu and the nesting destinations (latitudes) to which the birds were going.

From each download, BasTrak software generates a con-tinuous graph in which daily cycles of sunrise–daytime–sunset–nighttime are shown sequentially. With typical daily activities (foraging, standing, preening, etc.), the cycles are generally regular and “clean”, but when the geolocator is repeatedly shaded seemingly aberrant fluctuations between light and dark (herein referred to as “noise”) are recorded (Fig. 3). Noise was of particular interest when plovers were on breeding grounds since it was an almost certain indicator of shading during such activities as nest-building, incubation, and brooding of chicks (for details of the nesting cycle, see Byrkjedal & Thompson 1998, Johnson & Connors 2010). All 20 of the geolocators recovered contained light level data recorded on breeding grounds, 16 with noise and 4 without. Two of the latter (1 male, 1 female) were noise-free for the entire nesting season implying lack of pair formation (see Johnson & Connors 2010), and two geolocators malfunc-tioned shortly after the birds arrived on their nesting grounds. The 16 geolocators that archived noise yielded the following information: 12 birds (75%) had 29–69 consecutive days of noise (spans lengthy enough to exceed the incubation period of 25 days, Johnson & Connors 2010), thus suggesting suc-cessful hatching and in some cases brood rearing; 1 of the 12 successful birds had an initial noise-period of 11 days, then 10 clean days followed by 43 noise days, the most plausible explanation for this pattern was loss of an initial clutch fol-lowed by renesting (see Johnson et al. 2008); 4 of the 16 birds (25%) presumably failed in their nesting attempts as their noise-periods were relatively short (9–22 days), 2 of these individuals showed renesting patterns similar to that just described and thus apparently failed twice.

Fig. 1. Newly attached geolocator on a Pacific Golden-Plover. Metal band distal to the geolocator protects the ankle joint.

55°

60°

65° N

Fig. 2. The breeding ground destinations of 20 geolocator-equipped Pacific Golden-Plovers. The map includes two birds that probably failed to nest (see Results). The dashed line defines the approximate portion of Alaska in which the species breeds. The major nesting range of P. fulva extends westward across much of Siberia.

29Johnson et al.: Tracking of migrating Pacific Golden-Plovers between Hawaii and Alaska

Fig. 3. An example of daily light level records from a male plover on breeding grounds in Alaska. Beginning at upper left, graph shows a continuous segment of clean days (across the top of the figure) that transitions to an initial period of noise (middle of the figure), then the cycle repeats itself. This pattern likely represents loss of the first clutch followed by a renesting attempt that also ended in failure. Consecutive daily time periods are: sunrise (ascending yellow line), daytime (upper horizontal black line), sunset (descending blue line), nighttime (lower horizontal black line). For additional details concerning the daily graphs generated by BasTrak see Fox (2010).

Fig. 4. Geolocator records showing the 2009 and 2010 migratory tracks of plovers in spring (yellow) and fall (purple) between Oahu and Alaska. The span of the Hawaiian Archipelago is approximately equal to the length of the Hawaiian Is. label. Irregular angles comprising each track represent 12-hour legs (see text). Though indicated by straight lines, many of the legs probably followed sinuous pathways. Tracks in 2009 were more direct with fewer irregularities than in 2010. The eastward shift of pathways in 2010 along with several significantly off-course deviations in both spring and fall likely reflect interyear vagaries of winds (affecting the birds’ flight paths) and cloud cover (affecting the accuracy of the geolocator fixes, and possibly obscuring celestial navigation cues as well).

Fig. 5. On some flight legs, plovers (presumably with assistance from strong tailwinds) reached very high ground speeds. Shown here are the geo-locator tracks of three individuals that covered 12-hour segments of their 2009 northward migrations at apparent speeds of 167–185 kph. How potential margins of error (i.e., accuracy of geolocations at the beginning and end of each leg, yellow dots) may have affected the calculations is unknown, so these findings should be treated accordingly (see Results). Red dots indicate nesting locations of these birds.

30 Wader Study Group Bulletin 118(1) 2011

Departures from nesting grounds began on 3 July and continued until 24 August. Nine of the 18 southbound plo-vers (50%) including all that left in July (5 birds) made fall stopovers on the Alaska Peninsula. These ranged from 1 to 40 days, with almost all (8 birds) stopping toward the lower end of the peninsula at approximately 56°N and 1 bird near the opposite end of the peninsula at about 58°N. Seawater contact during these stopovers was recorded for only one individual. Fall returnees arrived back on Oahu over the period 8–27 August.

All migrations between Oahu and Alaska followed essen-tially direct north–south routes (Fig. 4), with the exception of three birds that appeared to track for a short distance along the Hawaiian Archipelago. The exceptions occurred in spring 2010 when two plovers apparently moved north-westward to the island of Kauai before turning northward, and in fall 2010 when one individual may have returned to Oahu via Kauai. Notably, two individuals in 2010 apparently missed Oahu during southward migration, then backtracked to reach the island. It is reasonable to assume that the variations evident in Fig. 4 (irregular east–west deviations during spring and fall passages, some far off course; differing lengths of 12-hour legs; and an eastward shift of pathways in 2010) are functions of intra- and interyear variability in wind direction, wind strength, and cloud cover that may obscure celestial cues.

Rough estimates of transoceanic ground speeds, lengths of the routes flown, and flight-times are summarized in Table 1. We emphasize that the values shown in the table are not based on precise measurements and should be treated with cau-tion. The flight tracks of plovers visualized on Google Earth (Fig. 4) depend on fixes obtained every 12 hours that are each affected by the margins of error inherent to all geolocator output; moreover such errors are greater for mainly latitudinal movements, as in our case, than longitudinal movements (see Methods). Average flight-times for the north and south pas-sages were on the order of 3 and 4 days, respectively; with extremes (presumably wind-related) ranging from around 1.5 to 5 days. There was considerable variation in the distance apparently traveled on individual 12-hour flight legs. Some were remarkably long (likely because of strong tailwinds) and thus traversed at relatively high speeds, others the opposite. Aside from the wind factor, unusually short 12-hour legs might in some instances represent situations where birds became disoriented and actually flew (wandered) consider-able distances within the span covered by the 12-hour fixes. Three examples of apparent high ground speeds of 167–185 kph during northward migration are depicted in Fig. 5. If it is assumed that the error associated with each fix is ±200 km, these speeds might have been as low as 134–152 kph or as high as 200–218 kph. None of the loggers recorded any seawater contact during transpacific flights. As there is no land on a direct route between Hawaii and Alaska, these migrations were all nonstop.

DISCUSSION

In the telemetry studies by Johnson et al. (1997, 2001a, 2004), territorial plovers wintering on Oahu were radio-tagged, then searched for during monitoring flights across breeding grounds in Alaska. Many tagged birds were relocated in the north, thus demonstrating strong connectivity between Oahu and Alaska. Given the limitations of small VHF transmit-ters, details concerning the actual transpacific passage were impossible to obtain. Also, because ground truthing was not feasible, it was often uncertain whether a relocated bird was actually nesting or en route to a nesting location elsewhere. Significant resolution of these unknowns has now been achieved through the use of geolocators.

For migrants moving southward in the mid-Pacific, the Hawaiian Archipelago presents a wide target stretching approximately 2,500 km from northwest to southeast. It seemed possible that this lengthy chain of islands might function as a navigational pathway, especially during fall migration when plovers are returning to a wintering loca-tion like Oahu near the southeastern end of the archipelago. However, we found almost no evidence for this other than possible infrequent short-distance linkage between Oahu and Kauai. Instead, our results indicate that migratory flights between Oahu and Alaska are typically direct averaging about 4,800–4,900 km (the great circle distance from Oahu to the mid-region of the Alaska Peninsula is approximately 3,900 km). That plovers might rest on the surface of the sea during the lengthy passage was ruled out by lack of salt-water contact with our geolocators, thus confirming nonstop flights that in some cases lasted up to about 5 days. Notably, the famed naturalist Henry W. Henshaw, a keen observer of plovers in Hawaii, pointed out a century ago that for these birds to alight on water was extremely rare occurring “per-haps never when in migration” (Henshaw 1910). Studies in 2009–2010 of logger-equipped plovers nesting on the Seward Peninsula, western Alaska, indicated autumn flights of about 6 days that bypassed Hawaii and continued on to insular wintering grounds much farther south (OWJ et al. unpubl. data). Thus, the full capability of Pacific Golden-Plovers for nonstop long-distance flight appears to be significantly greater than what is revealed from the passage between Hawaii and Alaska.

Our estimates of mean ground speeds and ability to remain aloft in migrating Pacific Golden-Plovers (58–63 kph, at least 5 days) are similar to other shorebirds tracked by satellite transmitters or geolocators during transoceanic flights: East-ern Curlew Numenius madagascariensis (50 kph, 5–6 days, satellite; Driscoll & Ueta 2002); Bar-tailed Godwit (60 kph, 5–9 days, satellite; Gill et al. 2009); Ruddy Turnstone (50–65 kph, 4–7 days, geolocator; Minton et al. 2010); Red Knot (27–55 kph (by our calculations), 6–8 days, geolocator; Niles et al. 2010). Present findings also are consistent with limited information from our previous telemetry studies in which plovers migrated in spring from Hawaii to Alaska, then shed the radios while on breeding grounds. Among the many radio-tagged plovers found during aerial monitoring in Alaska, it appeared that two individuals had been relocated soon after arrival – one at 70 h (2.9 days) on the Alaska Peninsula (John-son et al. 2004), the other at 90 h (3.7 days) at the Copper River Delta (Johnson et al. 1997).

This paper is based on a sample of birds from only one island in Hawaii and may not be altogether representative of elsewhere in the Hawaiian chain. Ideally, geolocators should be deployed at additional sites in the archipelago to more fully evaluate our present findings. Furthermore, it would be fruitful to conduct geolocator studies at wintering grounds

Table 1. Summary of estimated Pacific Golden-Plover flight perfor-mance during migrations between Hawaii and Alaska in 2009 and 2010 (all measurements are mean, SD, range). Note that these data are based on location fixes where the margin of error may be ±200 km (see Methods). Therefore they should be treated with caution.

Spring flights (n = 19)

Autumn flights (n = 18)

Ground speed (kph) 63±16 (45–106) 58±19 (38–112)

Distance flown (km) 4,802±638 (4,195–6,381) 4,944±941 (3,967–7,303)

Flight time (hours) 77±19 (36–104) 91±25 (35–130)

Flight time (days) 3.2±0.7 (1.8–4.3) 3.8±1.0 (1.5–5.4)

31Johnson et al.: Tracking of migrating Pacific Golden-Plovers between Hawaii and Alaska

south of Hawaii as almost nothing is known about plover movements in those more distant regions. We are currently analyzing geolocator data recovered from birds wintering in American Samoa (south Pacific) and Saipan (western Pacific) that should partially fill the void (OWJ et al. in progress). The nesting locations reported in this paper, together with previ-ous radio-tagging studies (Johnson et al. 1997, 2001a, 2004, OWJ et al. unpubl. data) and the Seward Peninsula findings mentioned above, all suggest that plovers wintering in Hawaii breed primarily in southerly regions of the Alaska nesting range. Fewer birds made stopovers in Alaska during spring migration (4 of 19, 21%) than during fall (9 of 18, 50%). Of the 13 plovers that stopped over, only three contacted sea-water implying that foraging was mostly on uplands.

The first shorebird study to equate geolocator light level fluctuation on breeding grounds (noise) with nesting was by Conklin et al. (2010) and involved logger-equipped Bar-tailed Godwits recaptured at a wintering ground in New Zealand. As in this paper (see Results), Conklin and his coworkers interpreted the length of noise periods (i.e., the number of consecutive days) as indicating either successful or un-successful incubation. Solid validation of the relationship between noise and nesting requires correlative evidence from breeding grounds, and our studies on the Seward Peninsula (OWJ et al. unpubl.) provide a measure of this. In 2010, we recovered geolocators (these had been deployed in 2009) from four male Pacific Golden-Plovers at their nests and in each case incubation was clearly correlated with concurrent noise. Furthermore, a fifth individual showing no nest-related behaviours was repeatedly observed in mid-June 2010 together with a female – a situation suggesting loss of a first nest with possible re-nesting in progress (see Johnson et al. 2008). This subsequently appeared to be the case as the male was later captured on a nest, and the pattern of noise recorded by his geolocator was essentially identical to Fig. 3. We urge additional studies involving logger-equipped shorebirds on breeding grounds to further clarify the noise/nesting relation-ship. Current findings suggest that noise readings alone (as when geolocators are recovered on wintering grounds) are a useful indicator of incubation from which success (hatching) or nest failure can be inferred.

ACKNOWLEDGEMENTS

The project was funded primarily by Brigham Young University – Hawaii through two sources: a faculty-mentored student research program, and a faculty professional development program. Additional support was provided by the Hawaii Audubon Society. We thank Gene Castagnetti, Director of the National Memorial Cemetery of the Pacific, for kindly allowing us to use that site as one of our study areas. Many individuals helped in the capture and recapture of plovers. This often involved early morning mist netting, and for their pre-dawn efforts we are especially grateful to Phillip Bruner, Andrea Bruner, Arlene Bucholz, Arleone Dibben-Young, Joshua Fisher, Sam Goldstein, Beverly Haid, Sue Hillmann, Lynn Mugaas, John Mugaas, and Sigrid Southworth. We are further indebted to Joshua Fisher for introducing us to the Super Talon net gun, a device that turned out to be an invalu-able tool for capturing plovers; and to Beverly Haid and Sue Hillmann who graciously provided lodging for OWJ and PMJ during periods of fieldwork. Alan Akagi, Cindy Lavulavu, and Lael Prince helped analyze portions of the geolocator

downloads. Phil Battley reviewed the manuscript and offered many helpful editorial comments.

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