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The degree to which individuals migrate among particular breeding, migration, and wintering sites can have important implications for prioritizing conservation efforts. Four subspecies of Dunlin (Calidris alpina) migrate along the East Asian-Australasian Flyway. Each subspecies has a distinct and well-defined breeding range, but their migration and winter ranges are poorly defined or unknown. We assessed the migratory connectivity of 3 of these subspecies by evaluating a dataset that encompasses 57 yr (1960-2017), and comprises more than 28,000 Dunlin banding records and 818 observations (71 recaptures and 747 band resightings). We present some of the first evidence that subspecific segregation likely occurs, with arcticola Dunlin wintering in areas of Japan, and other arcticola, actites, and sakhalina Dunlin wintering in areas of the Yellow and China seas. Observations indicate that whether an arcticola Dunlin winters in Japan or the Yellow and China seas is independent of their breeding location, sex, or age. Furthermore, observations indicate that ≥83% of arcticola Dunlin exhibit interannual site fidelity to specific wintering sites. This suggests that the degradation of specific wetland areas may negatively affect particular individuals of a particular subspecies (or combination of subspecies), and, if widespread, could result in population declines. Given the possible biases inherent in analyzing band recovery data, we recommend additional flyway-wide collaboration and the use of lightweight tracking devices and morphological and genetic assignment techniques to better quantify subspecies' migratory movements and nonbreeding distributions. This information, when combined, will enable effective conservation efforts for this species across the East Asian-Australasian Flyway. LAY SUMMARY The East Asian-Australasian Flyway has more threatened and near-Threatened migratory waterbird species than any other flyway in the world; however, developing flyway conservation plans has been challenging, in part due to limited information regarding population-specific migration patterns. Four subspecies of Dunlin migrate and winter along the East Asian-Australasian Flyway. Each has a well-defined breeding range; their migration and winter ranges are poorly defined or unknown. We assessed the migratory connectivity of 3 subspecies using data from 57 yr (1960-2017), which comprises more than 28,000 Dunlin banding records, 71 recaptures, and 747 band resightings. Subspecific segregation likely occurs, with arcticola Dunlin wintering in Japan, and other arcticola, actites, and sakhalina Dunlin wintering in the Yellow and China seas. It is likely that ≥83% of arcticola Dunlin exhibit interannual site fidelity to specific wintering sites. Our findings suggest that degradation of specific wetland areas may negatively affect particular individuals of a particular subspecies (or combination of subspecies) and could result in population declines.

Understanding spatial connectivity of long-distance migrants is important for effective management and conservation of both game and nongame species. Hunting of Nearctic-breeding shorebirds occurs in the Caribbean and northern South America; however, the origins of harvested individuals are generally unknown. We used stable hydrogen isotopes (δ2H) in feathers of juvenile shorebirds to infer the origins of birds harvested at 2 sites in Barbados using probabilistic assignments based on a terrestrial–freshwater δ2H isoscape. We used tissue δ13C and δ15N values to filter individuals that had derived nutrients from marine sources. Natal origins of juvenile American Golden-Plover (Pluvialis dominica), Stilt Sandpiper (Calidris himantopus), Short-billed Dowitcher (Limnodromus griseus), and Lesser Yellowlegs (Tringa flavipes) were predicted to be mainly from the eastern parts of their breeding ranges in eastern Canada, with American Golden-Plover, Stilt Sandpiper, and Short-billed Dowitcher also having h...

Semipalmated Sandpiper (Calidris pusilla) populations have undergone significant declines at core nonbreeding sites in northeastern South America. Breeding populations have also declined in the eastern North American Arctic, but appear to be stable or increasing in the central and western Arctic. To identify vulnerable populations and sites, we documented the migratory connectivity of Semipalmated Sandpipers using light-level geolocators, deploying 250 at 8 Arctic sites across the species' breeding range from 2011 to 2015, plus 87 at a single wintering site in northeastern Brazil in 2013 and 2014. We recovered 59 units and resighted 7 more (26% return rate) on the breeding grounds, but none at the nonbreeding site. We recovered only ∼3% of units deployed in 2013 at eastern Arctic breeding sites, but recovered 33% of those deployed in 2015. Overall, birds with geolocators were 57% as likely to return as those carrying alphanumeric flags. Stopover durations at prairie sites (mean: 8.7 days southbou...

Worldwide, shorebirds are a major component of rice field avian biodiversity. Rice fields in Argentina and southern Brazil hold large numbers of shorebirds and have been recognized as important areas for migrating or wintering species. To develop successful shorebird conservation strategies, we need to understand geographic variation in shorebird abundance in rice fields as well as how bird use of rice fields varies over the rice growing cycle. We surveyed shorebirds in November and December in the main rice cultivation regions of interior Argentina and coastal Brazil to estimate shorebird densities using distance sampling and to evaluate densities of individual species at different stages of the rice cycle. We detected >7,000 shorebirds in rice fields, including a variety of Nearctic migrants. Density of resident species was generally low and showed no differences between countries. Densities of migratory taxa were higher and varied between Brazil and Argentina. Pectoral Sandpiper (Calidris melanotos) and Lesser Yellowlegs (Tringa flavipes) were the most common species in Argentina, but White-rumped Sandpiper (Calidris fuscicollis) and American Golden-Plover (Pluvialis dominica) were the most common species in Brazil. Pectoral Sandpiper density was nearly 8 times higher in Argentina than in Brazil; densities of the White-rumped Sandpiper and American Golden-Plover were 33 and 25 times higher in Brazil than in Argentina. Shorebird density was highest in lightly flooded paddies with rice height 7000 aves playeras en los campos de arroz, incluyendo una variedad de migrantes neárticos. La densidad de las especies residentes fue generalmente baja y no mostró diferencias entre países. Las densidades de los taxa migratorios fueron mayores y variaron entre Brasil y Argentina. Calidris melanotos y Tringa flavipes fueron las especies más comunes en Argentina, mientras que Calidris fuscicollis y Pluvialis dominica fueron las especies más comunes en Brasil. La densidad de C. melanotos fue casi ocho veces mayor en Argentina que en Brasil; las densidades de C. fuscicollis y P. dominica fueron 33 y 25 veces mayores en Brasil que en Argentina. La densidad de aves playeras fue mayor en los arrozales someramente inundados con alturas de arroz < 20 cm. Nuestros resultados confirman la importancia de los arrozales para las aves playeras en el sudeste de América del Sur y enfatizan la necesidad de evaluaciones detalladas para asegurar que las prácticas de manejo de los agroquímicos y del agua son amigables con la biodiversidad. Instituto de Recursos Biológicos Fil: Dias, Rafael Antunes. Universidade Católica de Pelotas. Laboratório de Ecologia e Conservação; Brasil Fil: Blanco, Daniel E. Fundación Humedales/Wetlands International; Argentina Fil: Goijman, Andrea Paula. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; Argentina Fil: Zaccagnini, Maria Elena. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; Argentina

Estuarine intertidal habitats are heterogeneous, therefore migratory shorebirds are expected to forage in microhabitats where they can maximize their energy intake. Identifying proximate factors that migratory shorebirds use to accept or reject a particular habitat patch will help land managers make conservation and restoration decisions that provide the greatest benefits to shorebird populations during migration, a period of intense energy usage. We examined whether small semipermanent tidal channels were preferentially used by foraging Western Sandpipers (Calidris mauri) and Dunlins (C. alpina) during a spring migratory stopover in Bandon Marsh, an Oregon, USA, estuary. Further, we tested alternative hypotheses about how channels might be beneficial to shorebirds by examining infauna abundance, composition, and depth alongside channels compared with that in open mudflats. The densities of Western Sandpipers and Dunlins were at least 4 times higher along channels than in open mudflat habitats. I...

On the western coast of North America, several estuaries provide shorebirds with important win- ter and stopover habitat. These habitats include not only aquatic estuarine resources but also adjacent upland ag- ricultural lands. The extent to which shorebirds use estuarine vs. upland habitats at these stopover sites is difficult to quantify but crucial to designing strategies for their conservation. We measured stable isotopes (δ 13 C, δ 15 N) in whole blood of Dunlins (Calidris alpina) and their prey from two major estuaries in north Puget Sound, Washing- ton, USA, to estimate their relative use of estuarine vs. upland agricultural zones. We identified four isotopically distinct dietary inputs (agriculture high in 15 N, other agriculture, marsh/marine, and freshwater plume). Isotopic sampling and modeling was informed by movements and habitat use derived from radiotelemetry. This isotopic structure allowed us to conclude that these Dunlins obtained about 62% of the protein in their diet from agricul- tural lands and 38% from the estuary. Our results underline the urgent need to combine management of estuaries and upland agricultural areas in strategies for shorebird conservation.

The Dunlin (Calidris alpina) is a polytypic shorebird with complex patterns of distribution and migration throughout its holarctic range. We analyzed mark-re sighting data obtained between 1977 and 2010 from birds captured at two major staging areas in western Alaska to test the hypothesis that the migration patterns of Alaskan populations are a mixture of parallel and chain, similar to those of Dunlin populations in the western Palearctic. Birds marked on the Yukon—Kuskokwim Delta were found wintering in both Asia and North America, which documented the unexpected mixing of C. a. arcticola from northern Alaska and C. a. pacifica from western Alaska and contradicted our initial prediction of parallel migration pathways for these two subspecies. In its North American winter range C. a. pacifica segregated according to location of marking, confirming our prediction of a chain migration pattern within this population. Individuals of C. a. pacifica marked on the delta were resighted significantly fa...

During its fall migration stopover on mudflats in the upper Bay of Fundy, Canada, the Semipalmated Sandpiper (Calidris pusilla) is thought to feed primarily on the amphipod Corophium volutator (mudshrimp). Semipalmated Sandpipers typically use a peck-probe foraging strategy and, until recently, there had been little evidence of variability or opportunism in their foraging habits during this stopover. From 2006 to 2008 we recorded data on the sandpipers' foraging behavior and food availability at three commonly used mudflats. Behavior and food availability varied considerably at one site in one year. In 2006 at Grande Anse, where mudshrimp densities were exceptionally low and ostracod densities very high, the peck-probe strategy was almost completely abandoned for “skimming,” a foraging behavior novel in this species. Because of similarities between skimming and grazing, used by Western Sandpipers (Calidris mauri) to consume biofilm, we hypothesized that birds switched to skimming to feed on biof...

Relatively little is known about shorebird movements across the coast of northern Alaska, yet postbreeding shorebirds use this coastline extensively prior to fall migration. We deployed 346 radio transmitters on 153 breeding and 193 postbreeding shorebirds of five species from 2005 to 2007.We examined two hypotheses regarding postbreeding shorebirds' movements: (1) whether such movements reflect ultimate routes of southbound migration and (2) whether migration strategy (length of flights) or timing of molt in relation to migration (molt occurring in breeding or winter range) are more influential in determining postbreeding shorebirds' behavior. Semipalmated Sandpipers (Calidris pusilla) moved east, consistent with the direction of their ultimate migration, but patterns of other species' movements did not reflect ultimate migration direction. Timing of postnuptial molt appeared to have more influence over residence time and movements than did migration strategy. Postcapture residence time for the...

Trace-element analysis has been suggested as a tool for the study of migratory connectivity because (1) trace-element abundance varies spatially in the environment, (2) trace elements are assimilated into animals tissues through the diet, and (3) current technology permits the analysis of multiple trace elements in a small tissue sample, allowing the simultaneous exploration of several elements. We explored the potential of trace elements (B, Na, Mg, Al, Si, P, S, K, Ca, Ti, Cr, Mn, Ni, Cu, Zn, As, Sr, Cs, Hg, Tl, Pb, Bi, Th, and U) to clarify the migratory connectivity of shorebirds that breed in North America and winter in southern South America. We collected 66 recently replaced secondary feathers from Red Knots (Calidris canutus) at three sites in Patagonia and 76 from White-rumped Sandpipers (C. fuscicollis) at nine sites across Argentina. There were significant differences in trace-element abundance in shorebird feathers grown at different nonbreeding sites, and annual variability within a...

Subspecies Calidris canutus islandica of the Red Knot breeds on the arctic tundra of northeastern Canada and northern Greenland and winters along the coasts of northwestern Europe. During northward migration, it stops over in either Iceland or northern Norway. It has been assumed that it does the same during southward migration. Using ratios of stable carbon isotopes (delta(13)C) in whole blood, blood cells, and plasma, we investigated evidence for a stopover in Iceland en route from the breeding grounds to the Dutch Wadden Sea. With the expected diet (shellfish) and stopover duration at Iceland (12-15 days, maximum 17 days) and the turnover rates of blood cells (15.1 days) and plasma (6.0 days), Red Knots that stopped in Iceland should arrive with a blood (cell) delta(13)C midway between a tundra (-24.7 parts per thousand) and a marine value (-14.0 parts per thousand) and a plasma delta(13)C approaching the marine value (-15.3 parts per thousand). However, many adults arriving at the Wadden Sea had delta(13)C ratios in blood (cells) and plasma below these levels, and some arrived with clear tundra signals in blood cells, suggesting that they skipped Iceland during southward migration. Surprisingly, available data suggest this also to be true for juveniles during their first southward migration. The delta(13)C signature of second-year birds confirmed that they oversummered in the Wadden Sea. Our findings contradict the largely untested idea that juvenile shorebirds make more stopovers than adults as well as the idea that the migration between the Nearctic and Europe is necessarily a two-leg process.

Surveys based on double sampling include a correction for the probability of detection by assuming complete enumeration of birds in an intensively surveyed subsample of plots. To evaluate this assumption, we calculated the probability of detecting active shorebird nests by using information from observers who searched the same plots independently. Our results demonstrate that this probability varies substantially by species and stage of the nesting cycle but less by site or density of nests. Among the species we studied, the estimated single-visit probability of nest detection during the incubation period varied from 0.21 for the White-rumped Sandpiper (Calidris fuscicollis), the most difficult species to detect, to 0.64 for the Western Sandpiper (Calidris mauri), the most easily detected species, with a mean across species of 0.46. We used these detection probabilities to predict the fraction of persistent nests found over repeated nest searches. For a species with the mean value for detectabil...

Environmental light intensity is known to exert a strong influence on antipredation behavior by influencing prey vulnerability. However, an association between low light levels and increased predation risk is not well established empirically. For species that rely on visual detection of their predators, low light levels can hinder predator detection and thus increase predation risk. We examined the foraging behavior of migrating Semipalmated Sandpipers (Calidris pusilla) on a mudflat in the Bay of Fundy in New Brunswick, Canada as a function of time of day from dawn to dusk. Time of day was used as a surrogate for light intensity, assuming that, on average, light levels would be lower near sunrise and sunset. Sandpipers forage both day and night at low tide, which occurs at different times each day, thus disentangling the effect of light intensity from energy levels. Falcons make surprise attacks on sandpipers by leaving forest cover and flying low over the mudflat, rendering detection difficult ...

To assess potential changes in tundra-nesting bird populations relative to increased herbivory by growing Lesser Snow Goose (Chen caerulescens caerulescens) and Ross's Goose (C. rossii) populations, we estimated avian population densities in coastal tundra near Cape Churchill, Manitoba, Canada in June 1984, 1999, and 2000. We also compared bird abundance in altered and intact freshwater sedge (Carex spp.) meadows to assess bird response at a smaller spatial scale, the habitat patch. At the landscape scale, Herring Gull (Larus argentatus) densities were significantly greater in both 1999 and 2000 than 1984, and Semipalmated Sandpiper (Calidris pusilla) and Savannah Sparrow (Passerculus sandwichensis) densities were greater in 2000 than 1984. As a group, tundra-nesting passerine densities were significantly greater in 1999 than 1984. Dunlin (Calidris alpina) densities were significantly lower in 1999 than 1984, and many larger, ground-nesting birds declined in abundance and occurrence along transec...

As late as the 1940s the Semipalmated Sandpiper (Calidris pusilla) was the most abundant sandpiper breeding at Churchill, Manitoba. By the 1960s it had undergone a sharp decline, and by the mid-1990s the local population consisted of 11 pairs in a single colony. Nesting was last documented in 2001. Declines had also become evident at several other breeding sites along the Hudson Bay coast of Manitoba and Ontario, as well as in the number of migrants detected on the Atlantic coast of Canada and the northern United States. Information on the biology of the Churchill population in 1993–2004 largely agreed with that gathered at La Pérouse Bay, Manitoba, in the 1980s: reproductive success was good and new birds continued to join the colony; however, the number of breeding attempts by individuals was low and decreasing. As there is no evidence that the decline was related to local factors (e.g., altered habitats, climate change), it is probably attributable to mortality in the nonbreeding season, which leaves fewer birds available to return north. Whether causality can be fully resolved is problematic. Monitoring migrants can reveal population trends and studies on the breeding grounds can help frame hypotheses, but both approaches are time-consuming and provide only partial answers. In such cases, restoration of declining species may be best served by fostering habitat conservation throughout a species' range.

We examined diurnal time-activity budgets of American Avocets (Recurvirostra americana). Long-billed Dowitchers (Limnodromus scolopaceus), Stilt Sandpipers (Calidris himantopus). Semipalmated Sandpipers (C. pusilla), and Least Sandpipers (C. minutilla) in the Prairie Pothole Region of northwestern North Dakota during spring and fall 1994 and 1995 to evaluate the importance of prairie pothole wetlands to a variety of shorebird guilds. Long-billed Dowitchers, and Stilt, Semipalmated, and Least Sandpipers spent most of their time feeding in spring and fall. American Avocets also used prairie potholes for feeding, but other activities like locomotion, body maintenance, and sleep consumed large proportions of time. Time spent in various behaviors was similar among three diurnal (early, midday, and late) time periods during spring and fall. Avocets and dowitchers slept more during midday than early or late periods. Flock size was smaller during spring than fall in both years for American Avocets, Long-billed Dowitchers, Semipalmated Sandpipers, and Least Sandpipers and in 1994 for Stilt Sandpipers. More than half of all aggressive encounters by American Avocets, Stilt Sandpipers, Semipalmated Sandpipers, and Least Sandpipers were intraspecific during feeding. Smaller flock sizes in spring may be related to avoidance of costly aggression in spring and/or the numbers of birds migrating through the region. The Prairie Pothole Region serves as a stopover for most shorebirds to acquire energy reserves during migration, and conservation efforts should focus on preserving and enhancing prairie potholes for foraging shorebirds.

We corrdinated censuses from April 1988 to April 1995 to obtain an overview of shorebird abundance and distribution in Pacific Coast wetlands of the contiguous United States. We attempted to acquire at least 3 years of data for all major wetlands from counts within a short time window each fall, winter, and spring. Fourteen abundant, 8 moderatcly abundant, and 21 rare-to-uncommon species were recorded. For temperate-zone breeders. peak periods of abundance were fall or winter and, when discernible for arctic breeders, mostly fall or spring. Arctic breeders were relatively more abundant than temperate-zone breeders in Oregon and Washington wetlands. All five of the most abundant temperate breeders were limited primarily to California wetlands in all seasons. Only for Western Sandpiper (Calidris mauri) and Dunlin (C. alpina) did the estimated total individuals present simultaneously in all wetlands exceed 100.000. Fifty-six of 66 sites surveyed had at least four counts and at least 100 shorebirds on one or more counts; 38 of the 56 sites held at least 1% of 1 of 13 key species during at least one season. San Francisco Bay accounted for 24-96% of the estimated totals for key species; Grays Harbor, Willapa Bay, Humboldt Bay, Tomales Bay, Point Reyes Esteros, Bolinas Lagoon, Elkhorn Slough, Morro Bay, Mugu Lagoon, Bolsa Chica, Mission Bay, and San Diego Bay held at least 1% of at least half the key species in at least one season. The usefulness of five criteria for selecting key wetlands for shorebird conservation are examined and potential threats are discussed.

During spring migration, thousands of shorebirds gather in Delaware Bay at the same time as horseshoc crabs (Linudus polyphemus) are spawning. During their stopover, the birds store enough fuel in the form of fat and muscle protein to complete their migration to the Canadian breeding grounds. We documented the changes in body mass of shorebirds migrating through Delaware Bay and determined how much of the shorebird diet during this period consisted of horseshoc crab eggs. Migrating shorebirds were captured, morphometric measurements taken, and gut samples collected by stomach flushing. Red Knots (Calidris canutus). Ruddy Turnstones (Arenaria interpres), Sanderlings (C. alba), and Semipalmated Sandpipers (C. pusilla) increased their body mass up to 70-80% while staging on Delaware Bay. Horseshoe crab egg membranes constituted the bulk of the gut contents for all species at all collection sites. Polychaete and oligochaete worms were found in substantial concentrations in gut samples collected from shorebirds in certain beaches. Sand and unidentified decomposed material were found in varying amounts in gut samples of all species and locations. Apparent declines in spawning horseshoe crab populations may adversely affect migratory shorebirds.

We describe stopover ecology for 132 migrant radiomarked Western Sandpipers (Calidris mauri) relocated repeatedly along the Pacific Flyway of North America. Eighty-eight percent of radiomarked birds were detected at 1-5 sites north of their banding sites, at distances ranging from 240-4,000 km away. We compare length of stay and physical indices of Western Sandpipers banded at coastal sites (San Francisco Bay, California and Grays Harbor, Washington), and an interior, western Great Basin site (Honey Lake, California). Western Sandpipers radiomarked at the interior site had significantly shorter length of stays than birds radiomarked at coastal sites, and they had significantly lower fat scores. The ephemeral nature of Great Basin stopover sites and an increased risk of predation may explain some of this variation. Fat and body condition indexes explained little of the observed variation in length of stay of Western Sandpipers at banding and other stopover sites. Length of stay of birds radiomarked at Grays Harbor were significantly longer compared to birds radiomarked to the south that also stopped at Grays Harbor, suggesting a potential capture effect on length of stay of birds at banding sites. Mean length of stays at seven sites other than banding sites ranged from 1.1-3.3 days and were not significantly affected by sex of bird, year of study, or banding location. Length of stay of male Western Sandpipers at the Copper River Delta, Alaska became significantly shorter later in the migration period, but not for females. Coastal sites along the Pacific Flyway from San Francisco to the breeding grounds generally function as stopovers for Western Sandpipers instead of staging areas.

Surveys of California's Central Valley between 1992-1995 document it as one of the most important regions in western North America to migratory and wintering shorebirds. Populations averaged 134,000 individuals in August, 211,000 in November, 303,000 in January, and 335,000 in April. Of 33 species, the 10 or 11 that averaged over 1,000 individuals each season accounted for 99% of total numbers. Managed wetlands, agricultural fields (especially rice), and agricultural evaporation ponds held the most shorebirds. Species varied their seasonal, geographic, and habitat use of the Central Valley, primarily in response to changes in water availability from rainfall or management practices and latitudinal variation in habitat availability mediated, in part, by climate. In the record rainfall year of 1994-1995, shorebird numbers increased 74% between November and January, primarily from coast-to-interior movements of the Dunlin (Calidris alpina) and Long-billed Dowitcher (Limnodromus scolopaceus) and local habitat shifts of Killdeer (Charadrius vociferus). Although the Valley's shorebirds face threats from poor or toxic water quality, changing agricultural practices, and habitat loss to urbanization, they should benefit from current efforts to increase flooding of rice fields and to secure a stable high quality water supply for wetlands. Development of a sound conservation strategy is crucial for the preservation of shorebird populations in the Central Valley, as this agriculturally-dominated landscape is among the most altered in North America and remains vulnerable to strong economic and population growth pressures that may impact shorebird habitats in the future.

Playas in the Southern High Plains (SHP) are important for migrant shorebirds, but the functional role of playas to migrant shorebirds is not clearly understood. We conducted diurnal time-activity budgets on American Avocets (Recurvirostra americana), Long-billed Dowitchers (Limnodromus scolopaieus), Least Sandpipers (Calidris minutilla), and Western Sandpipers (C. mauri) in spring and fall 1993 and 1994 in 69 playas on the SHP of Texas. During both seasons, Least and Western Sandpipers spent 70-80% of their time feeding. Long-billed Dowitchers spent 77% of their time feeding in spring, but spent more time sleeping and less feeding in fall. American Avocets spent 41-50% of their time feeding and 34-40% of their time sleeping during each season. All four species spent minimal time engaged in locomotion, body maintenance, alert, and aggressive behaviors. American Avocets and Long-billed Dowitchers fed most during the midday and late periods and slept most during the early period. Least Sandpipers fed most during the early period, whereas feeding activities of Western Sandpipers remained 70-80% throughout the day. Each of these species use different behavioral strategies in response to such factors as migration distances, energetic needs, differential predation. nocturnal foraging, and diet. Playas appear to serve as important intermediate stopover sites for shorebirds during migration.

We monitored the inter-wetland movements of 115 radio-tagged Pectoral Sand-pipers (Calidris melanotos) at three migration stopovers in the Great Plains of North America during April and May from 1992 to 1995. While resident at a stopover, individuals were very localized in their movements. Over 40% of the birds made no inter-wetland movements, and over 90% of individuals moved less than 10 km from their original release site. Characteristics of wetlands where birds were released did not affect bird movements. However, the structure of the surrounding landscape explained up to 46% of variation in individual bird movements. As the distance between wetlands decreased, and the proportion of the landscape composed of wetlands increased, individual birds moved between wetlands more frequently and moved longer distances from their release site. These movement patterns indicate that a more connected landscape allows shorebirds to exploit more feeding sites with reduced searching costs; a result consistent with foraging theory. We estimate a degree of landscape connectivity at which a wetland complex functions as a single large wetland as measured by sandpiper feeding patterns. Our data provide support for the idea that complexes of small, closely spaced wetlands can be important migration stopovers and may have significant conservation value.

I examined the foraging behavior of Sanderlings (Calidris alba) and Semipalmated Plovers (Charadrius semipalmatus) during their spring stopover period along the Atlantic coast of southern New Jersey following an oil spill. I used focal animal sampling to test the null hypothesis that there are no differences in foraging behavior as a function of the degree of oiling of birds. Nearly 50% of the foraging time of shorebirds was interrupted during the main period of beach oiling, primarily by clean-up personnel and vehicles that moved up and down the oiled beach, compared to less than 5% of the foraging time disruption at a control beach where birds were interrupted only by walkers and joggers. For both species, the time devoted to feeding decreased significantly, whereas the time devoted to standing about and preening increased significantly as percent of oiled plumage increased. For shorebirds that are already time-stressed in their refueling efforts before their long journey to arctic breeding grounds, these interruptions may prove fatal or might lower reproductive success once they reach the breeding grounds.

Throughout coastal regions of the world, pasturelands often augment important and declining intertidal foraging habitats for nonbreeding shorebirds (Suborder Charadrii). Little is known, however, about factors influencing bird use of pastures. Hence, we examined the spatial distribution of shorebirds in coastal pastures near Humboldt Bay, California from October 1991-May 1992 and correlated spatial distribution patterns with environmental and habitat variables. Shorebirds used pastures in a nonrandom (clumped) fashion. Pasture use varied seasonally for Killdeer (Charadrius vociferus), Marbled Godwit (Limosa fedoa), and Common Snipe (Gallinago gallinago); Dunlin (Calidris alpina) and Black-bellied Plover (Pluvialis squatarola) use increased when it rained, and Dunlin, Black-bellied Plover, and Killdeer use increased nearer the time of a new moon. At the level of the individual pasture, the likelihood of encountering most species (5 of 6) increased as vegetation height decreased. The likelihood of pasture use by Dunlin and Killdeer increased when shorebirds used pastures the previous week. Extensive, nonrandom use of coastal pastures by nonbreeding shorebirds indicates that conservation planning for shorebirds should consider habitat characteristics. In the vicinity of Humboldt Bay and other coastal bays, use of pastures by shorebirds can be increased by practices that provide short vegetation. Although shorebird use did not correlate with use of pastures by cattle, grazing by livestock is probably the means by which to achieve habitat characteristics attractive to shorebirds while maintaining compatible human uses on private lands. Regular use of some pastures by shorebirds indicates that site faithfulness may be important and that traditional sites need to be identified and protected.

To determine whether Calidris paramelanotos is a distinct species or a hybrid, DNA sequences from the mitochondrial cytochrome-b gene were obtained from it, as well as from C. ferruginea and C. melanotos. The sequences of the first two taxa were identical whereas that of C. melanotos differed by 9%. It is argued that C. paramelanotos is a hybrid taxon with C. ferruginea constituting the maternal parent. This conclusion, combined with comparisons of protein allozyme variation effectively rule out all but one of the crosses postulated for its hybrid origin -C. ferruginea x C. melanotos.

We studied the migratory movements of radio-equipped Western Sandpipers (Calidris mauri) along a 4,000 km stretch of the west coast of North America from California to Alaska during the 1992 spring migration. A total of 77 shorebirds were radio-tagged at San Francisco Bay, CA ; Bolinas Lagoon, CA ; Fraser River Delta, British Columbia ; and the Stikine River Delta, AK. Daily aerial and ground monitoring from mid-April to late May at banding sites as well as the Copper River Delta provided data on length of stay of individual shorebirds and migration times between study areas. Fifty-eight shorebirds were detected beyond banding sites for a 74% net relocation rate. The proportion ofbirds detected along the migration route increased with latitude : Grays Harbor, WA (3.4%) ; Fraser River, British Columbia (8.6%) ; Stikine River, AK (28.6%) ; and Copper River, AK (62.3%). Length of stay averaged three days per site. We failed to detect differences in length of stay among sites or between sexes. A condition index calculated as body mass standardized for body size was a poor indicator of length of stay at a site or migration time among sites. An estimated 26% of radio-equipped birds were never relocated suggesting that migrant birds use smaller dispersed wetlands as well as the major intertidal wetland complexes we studied. We conclude that most spring migrant Western Sandpipers use a short-flight hopping migration strategy rather than a few sustained long flights. The short-flight strategy emphasizes the importance of maintaining a continuous complex of intertidal wetland habitats along the migration route to ensure shorebird conservation.

Parasitic Jaegers (Stercorarius parasiticus) are thought to rely exclusively on kleptoparasitism of seabirds to obtain their food while on migration. We investigated this dependence of fall migrating birds at a stopover located on the shore of the St. Lawrence River, Quebec. We found that in addition to kleptoparasitism, jaegers also preyed upon invertebrates (Gammarus spp.), ducks, and shorebirds. Small Calidris sandpipers were chased more often than expected according to their availability whereas Black-bellied Plovers (Pluvialis squatarola) were chased less often. The capture rate was independent of the type of shorebird chased. Capture rate was not influenced by the number of jaegers (one to five) participating in a chase. The number of jaegers, however, significantly affected the per capita hunting yield through prey defense against gulls; pair members obtained the highest yield. Predation of shorebirds was mainly performed by territorial jaegers which restrained other jaegers from the main hunting area. Kleptoparasitic interactions were mostly aimed at Common Terns (Sterna hirundo), which were chased more often than expected considering their availability, whereas Black-legged Kittiwakes (Rissa tridactyla) and Ring-billed Gulls (Larus delawarensis) were chased less often. Terns were more likely to drop food than kittiwakes. The success rate at inducing a tern to drop a fish increased with jaegers' group size (one to seven), whereas the per capita feeding yield decreased. No such trend was observed when jaegers chased kittiwakes. Occurrence of predation and kleptoparasitic events was influenced by tide and time of day.

Semipalmated Sandpipers (Calidris pusilla) stop at staging areas during migration to replenish fat reserves that fuel long distance flights. We hypothesize that if sandpipers are minimizing time spent en route between wintering areas and breeding grounds, a negative correlation should exist between fat content upon arrival at a staging area and length of stay. We examined the relationship between these two variables at a spring staging area in coastal South Carolina using simple and multiple regression models. Length of stay was independent of estimated fat content at capture after controlling for date in the season. Birds with sufficient energy reserves for long distance flights were as likely to remain on the study area as lean birds. Date in the season showed more influence on stopover time than estimated fat mass at capture. Stopover time decreased with later date, suggesting an increase in the speed of migration as the season progressed. These results show that date is a critical variable influencing Semipalmated Sandpiper migration stopover strategy. Migrants appear to shift their migration priorities with respect to fat stores and stopover time as the season progresses

Arctic-nesting shorebirds require several refueling stops during their long migrations between breeding grounds and Central and South American wintering areas. The protection of stopover habitats for transcontinental migrants depends on whether birds fly long distances between a few select sites or fly short distances and stop at several wetlands. Although the Great Plains historically provided a vast array of wetlands for use by migrants, wetland loss and conversion have reduced the availability of stopover sites in recent decades. In this study, we examined (1) residency periods, (2) fat dynamics, and (3) migration chronology of two shorebird species, the Semipalmated Sandpiper (Calidris pusilla) and Whiterumped Sandpiper (C. fuscicollis) at Quivira National Wildlife Refuge (NWR), Kansas. Semipalmated Sandpipers had prolonged periods of species residency with overlapping arrivals and departures. Individual residency periods were highly variable and were unrelated to lipid reserves upon arrival. In contrast, White-rumped Sandpipers arrived and departed more synchronously. Birds that arrived in poor condition stayed longer than those with more body fat in 1991, but not in 1992. Wind direction did not influence patterns of departures of either species. We hypothesize that Semipalmated Sandpipers are ecologically eurytopic when migrating across the Great Plains in the spring. Highly variable patterns in arrival, residency, and lipid levels indicate that spring migration of this species is relaxed and opportunistic. White-rumped Sandpipers showed a pattern of reduced flexibility. Flight range estimates suggest that most birds require intermediate stopovers before reaching the breeding grounds. Interior wetlands appear to function as migration stopovers rather than staging areas for shorebirds.

Estimation of lean mass and lipid levels in birds involves the derivation of predictive equations that relate morphological measurements and, more recently, total body electrical conductivity (TOBEC) indices to known lean and lipid masses. Using cross-validation techniques, we evaluated the ability of several published and new predictive equations to estimate lean and lipid mass of Semipalmated Sandpipers (Calidris pusilla) and White-rumped Sandpipers (C. fuscicollis). We also tested ideas of Morton et al. (1991), who stated that current statistical approaches to TOBEC methodology misrepresent precision in estimating body fat. Three published interspecific equations using TOBEC indices predicted lean and lipid masses of our sample of birds with average errors of 8-28% and 53-155%, respectively. A new two-species equation relating lean mass and TOBEC indices revealed average errors of 4.6% and 23.2% in predicting lean and lipid mass, respectively. New intraspecific equations that estimate lipid mass directly from body mass, morphological measurements, and TOBEC indices yielded about a 13% error in lipid estimates. Body mass and morphological measurements explained a substantial portion of the variance (about 90%) in fat mass of both species. Addition of TOBEC indices improved the predictive model more for the smaller than for the larger sandpiper. TOBEC indices explained an additional 7.8% and 2.6% of the variance in fat mass and reduced the minimum breadth of prediction intervals by 0.95 g (32%) and 0.39 g (13%) for Semipalmated and White-rumped Sandpipers, respectively. The breadth of prediction intervals for models used to predict fat levels of individual birds must be considered when interpreting the resultant lipid estimates.

Northbound migrant shorebirds (Charadridae and Scolopacidae) were surveyed weekly by air on Delaware Bay beaches on the Atlantic coast of North America in May-June 1986 through 1992. The single day peak count occurred between 26-30 May when an average of more than 216,000 birds was counted. The most abundant species were Semipalmated Sandpiper (Calidris pusilla), Ruddy Turnstone (Arenaria interpres), Red Knot (Calidris canutus) and Sanderling (Calidris alba). Our surveys documented high hemispheric counts for each of these species, and established Delaware Bay as the most important spring stopover in the eastern U.S. for these shorebirds. Counts of Sanderlings and Semipalmated Sandpipers declined significantly over the seven years; no trends for other species were detected. Differences among species in distribution along bay beaches were attributable partly to habitat factors. We suggest that a thorough understanding of shorebird abundance and habitat use in Delaware Bay is necessary to develop a conservation strategy for regulatory protection and conservation of migrant shorebirds using this area.

We review the status of North American migrants in Amazonia and present recent records of the authors and co-workers. We report migration dates, maximum counts and new distributional information for 45 species. Included are the first Brazilian records of Piranga olivacea, the first Brazilian specimens of Contopus virens, and records of several shorebirds primarily restricted to coastal areas in South America that were previously unrecorded from inland Amazonia. Amazonia is south of the main wintering areas for most North American passerines; however, at least eight species winter primarily in Amazonia. Amazonia appears to be an important migratory route for many shorebirds, including major portions of the populations ofPluvialis dominica, Calidrisfuscicollis, and Calidris melanotos.

We studied the foraging behavior of Sanderlings (Calidris alba) in the winter of 1986, 1988 and 1990 in Florida to determine whether the presence of people influenced foraging behavior, and whether foraging behavior varied as a function of time of day. We used a focal animal sampling approach. For all three years, the models explaining the greatest variation in seconds per minute devoted to feeding included the number of people within 100 m of foraging Sanderlings. Although the number of people within 10 m of foraging Sanderlings during the day did not increase from 1986 to 1990, the number of people within 100 m rose dramatically, and foraging time per minute decreased. Sanderlings continued to feed through dusk into night and the time devoted to foraging and to aggression was greater at night, while the time devoted to avoiding people was less at night than during daylight or dusk.

Birds rely largely on dietary calcium to produce eggs because they have limited calcium reserves (see Gilbert 1983). Diets consisting of fish and shellfish may contain sufficient amounts of calcium for egg production (Gilbert 1983), but insects (Turner 1982) and seeds and foliage (Scott et al. 1976, Gilbert 1983) contain too little calcium to maintain observed rates of laying. Swallows (Hirundo rustica), for example, lay one egg per day, and they have about 16 hr of daylight for foraging. Yet, on a diet of insects they would have to forage for 12 to 36 hr, depending on the weather, to obtain enough calcium for a single egg (Turner 1982). Laying hens, which produce eggs even while on lowcalcium diets, adjust their laying rates so that the amount of calcium output in eggs and urine matches input from the diet (Gilbert et al. 1981). Calcium deficient diets result in reduced eggshell thickness (Gilbert et al. 1981), reduced clutch size (Dale 1955, Greeley 1962, Chambers et al. 1966, Krapu and Swanson 1975), and reduced hatching rates (Krapu and Swanson 1975). Typical rates of egg production are maintained by increasing calcium input. Reproductive hens can absorb calcium from the digestive tract more efficiently than non-reproductive hens, and they increase the amount of calcium in their diet on laying days (see Gilbert 1983). Depending on what is available, they increase calcium intake by eating more food, more calcium-rich foods, and calcareous grit (see Gilbert 1983). Wild birds also increase the amount of calcium in their diets during the laying period. Among studies of food habits, it is commonly observed that bone fragments (MacLean 1974), mollusk shell (Jones 1976, Davies 1977, Beasom and Pattee 1978, Ankney and Scott 1980) and calcareous grit (March and Sadleir 1972, Jones 1976) appear in the diets of birds during the breeding season whereas they are less common or absent at other times of the year. Detailed information indicates that intake of supplemental calcium is closely associated with laying (Jones 1976, Beasom and Pattee 1978, Ankney and Scott 1980). Little is known about how wild birds actually obtain calcium for egg production. They may be able to acquire it incidentally during other activities if the source is abundant and widespread, or they may have to expend considerable effort to obtain it if it is rare or localized. Both situations probably occur. For example, MacLean (1974) observed that raptor pellets, the most likely source of calcium for the arctic sandpipers (Calidris spp.) that he studied, were extremely abundant. Band-tailed Pigeons (Columbia fasciata), on the other hand, congregate at mineral springs during a discrete portion of the breeding season to obtain salt-coated gravel (March and Sadleir 1972), suggesting that individual birds move quite some distance to obtain supplemental calcium. The swallows studied by Turner (1982) spent about 30 minutes per day obtaining calcareous grit. We report here anecdotal observations of breeding female Red-cockaded Woodpeckers (Picoides borealis) obtaining and caching bone fragments. Although sources of calcium were available within the home ranges of the birds that we studied, they were not abundant, and individual birds made distinct moves to go to them. That the birds cached bone fragments was particularly interesting because it appears to be in discordance with the usual adaptive explanations of food caching: stockpiling resources for periods of extreme need, forestalling the natural decline of a resource, and garnering time for activities other than foraging (see Sherry 1985, Vander Wall 1990). We suggest that bone fragments were cached for more immediate benefits resulting from the economics of handling individual pieces. These circumstances are similar to those in which food caching might have originated.

We studied the validity of predictive equations for total body fat in shorebirds based on external morphology and body mass with data from Sanderlings (Calidris alba) collected in New Jersey, Texas, Panama, and Perui. Equations derived at any one of these locations are not valid when applied to the other locations because changes in body mass involve both changes in fat and lean mass and because structural differences exist between these populations. We recommend that equations to predict total body fat in shorebirds derived at one location should not be applied to a different geographic area.

We examined differential migration in the Western Sandpiper (Calidris mauri) with respect to body size and wing chord allometry within sex and age categories. Culmen and wing chord data were collected as indices of structural body size at three sites that vary latitudinally: Ecuador, Panama, and Mexico. Within all sex and age categories, larger individuals (i.e., those with longer culmens and wing chords) and those with a disproportionately longer wing chord relative to the culmen migrated farther south. Our results, coupled with known molting schedules, indicate that i) immature sandpipers that grow disproportionately longer primary feathers on breeding grounds migrate farther during their first southward migration, and ii) adults that fly farther grow disproportionately longer primary feathers on the nonbreeding grounds. Although no single-factor hypothesis accounts for all aspects of age, sex, and size of Western Sandpiper distributions, costs associated with flight during migration play a significant role in determining differential nonbreeding latitudinal distributions.

In the winters of 1998–1999 and 1999–2000, we tracked 67 radio-marked Dunlin (Calidris alpina) throughout the complex agricultural landscape of the Willamette Valley of Oregon. Individual birds were tracked across 8-week sampling periods and indicated a high degree of regional fidelity throughout the three winter sampling periods. Birds exhibited varied degrees of fidelity to specific wetland sites and were detected at an average of nine different sites. Distances traveled within the region were extensive and greatest during late winter. Females ranged farther from capture sites than males, and movement from capture sites for all birds was greatest during late winter. Mean home-range size (95% minimum convex polygons) of birds was 258.2 ± 44.8 km2 (SE) and was greatest during late winter. Diurnal roosts were identified as centers of activities and daily movements were most pronounced during crepuscular periods. These data represent the most extensive documentation of winter movements for a shoreb...

We estimated local annual survival of 1,051 individually color-banded Dunlin (Calidris alpina) at Bolinas Lagoon, California from 1979 to 1992. Resighting rates for birds banded as adults varied significantly among years, and resighting rates for first-year birds varied by sex and year. No significant differences in local survival rates were found between males and females in any age classes. First-year birds had lower local survival rates than adults. We suspect that raptor predation accounted for much of this difference and other variation in survival rates. Adult Dunlin had lower local survival rates in the year of capture than in subsequent years. Variation in resighting of some groups of individuals including transient Dunlin may account for some differences. However, capture and release of Dunlin may induce short-term behavioral changes that increase the risk of depredation by avian predators within the first few days after capture.

Plovers (Charadriidae) and sandpipers (Scolopacidae) exhibit a distinct difference in foraging behavior. Plovers typically move by alternating stationary periods with short runs, either attempting prey capture by picking or stopping again at the end of a run. Sandpipers typically move steadily over the substrate and either pick prey from the surface or probe beneath it. Some sandpipers feed visually like plovers, but they do not share the plovers' run-stop-peck foraging mode. As this rather distinct difference between members of the two families is characteristic, is of importance in distant field identification, and is of interest theoretically, any deviation from the family type is worth documenting. I observed such a deviation at Dungeness Spit, Clallam County, Washington, on 8 January 1989. About 20 Black-bellied Plovers (Pluvialis squatarola) foraged along the sandy beach on the bay side of the spit as the water level began to drop from the high-tide point just after midday. Small flocks of Dunlins (Calidris alpina) and Sanderlings (C. alba) fed in the same area. The sky was heavily overcast, with a slight wind and very little wave action. The temperature hovered around freezing, and it began to snow soon after these observations were made. The plovers were watched at some length as they foraged. The birds were flushed regularly by human intruders, so I could not determine how many plovers fed by this method, but it was at least five individuals. Most birds foraged in water 1-3 cm deep, and they did so consistently by walking slowly, in the manner of a foraging sandpiper, and picking at the surface at short intervals. Dunlins foraged with them in the same way and also probed underwater, while Sanderlings foraged along the shore. I did not assess foraging success for any of the species, but all were actively picking from the water or sand surface. I could not determine the plovers' prey items, which must have been small. Most of them foraged singly with small groups of Dunlins, and I saw no aggressive interactions between plovers. Individuals of all three species were also roosting at the same time. The tide was sufficiently high that the plovers had li tle intertidal substrate exposed for foraging. Even more significant, the low temperature may have made foraging on solid substrates relatively unproductive for a visual forager by reducing prey numbers at the surface (Evans 1976, Pienkowski 1981). Thus the plovers took advantage of an alternative source of prey, in the nearshore water column and on the surface. The typical run-stop-peck foraging strategy would not be effective in water, so a plover foraging in that medium cannot use it.

Display Flights (DFs) of the Least Sandpiper (Calidris minutilla) are described. DFs were prolonged flights (averaging 1.2 min in Manitoba and 3.4 min in Nova Scotia), about lo-30 m in altitude, by unmated males over their future nesting areas. Displaying males alternated brief glides and bouts of rapid shallow wingbeats (Flutters) throughout DFs; the two phases averaged 0.84 and 0.72 s, respectively. Flutters averaged 26 (Yukon) to 37 per min (Nova Scotia). DFs ended in several kinds of descents, from slow parachuting to rapid stooping. Three main call types were associated with DFs. The main Display Flight Vocalization (DFV) was simple and stereotyped, and was emitted rhythmically throughout DFs. DFVs of 22 males averaged 390 ms long with intervals between them of 106 ms. DFVs thus occurred at a rate of about two per second, so were not synchronized with Flutters. Some features of DFs, such as their monotonous, repeated calls, are shared with many other open-country species with aerial displays (e.g., plovers, pipits). Nevertheless, DFVs are probably plesiomorphous within the Calidridinae. The adaptive significance and ancestral/derived status of these and other features of DFs are discussed. The Calidridinae (Scolopacidae) consists of 24 closely related species of sandpipers that nest in open habitat in the arctic and subarctic (Pitelka et al. 1974). Their ecological similarities and close affinities make them ideal for study of adaptive radiation and homologies of displays in a non-passerine group. A good candidate for such study is aerial display, which is well developed in open-country species in general, and occurs in numerous charadriiform species, including Calidridinae (Armstrong 1963, Pitelka et al. 1974). In this paper I provide a detailed description of aerial displays in a representative calidridine, the Least Sandpiper (Calidris minutilla). This will establish a baseline for future comparative studies, thereby permitting assessment of the relationship of the display’s structural features to the different species’ spacing and mating systems, and allowing the species’ affinities to be considered. C. minutilla is a subarctic species whose nesting ‘range extend$ from the Alaska Peninsula to Newfoundland, with some birds breeding as far south as Massachusetts and Nova Scotia (Anderson 1980, Johnsgard 198 1). Males of this monogamous species occupy the nesting grounds each spring in advance of females and establish ephemeral territories over which they give Display Flights (DF; see Appendix for a list of abbreviations). Males stop displaying when they acquire a mate, although they nest in the area over which they displayed. Both sexes incubate and care for the brood, but adults and chicks generally feed in undefended areas distant from the nesting grounds. Males assume an increasing role in incubation as it proceeds, and are mainly responsible for raising the brood (Miller 1977, 1979a). The aerial displays of unpaired males in this species are very restricted in occurrence and function: a male may engage in display flights for only a few days each spring, and these apparently serve solely to attract a female to a suitable nesting area, while simultaneously repelling competing unpaired males. STUDY AREAS AND METHODS I studied Least Sandpipers at three locations: Sable Island, Nova Scotia (43”57’N, 59”55’W) from 17 May to 23 July 1975, and 14 May to 3 August 1976; near Churchill, Manitoba (58”24’N, 94”24’W) from 24 May to 6 July 1978; and in the Blackstone River Valley, Ogilvie Mountains, Yukon Territory (64”39’N, 138”27’W) from 30 May to 2 June 1979. Many birds were individually color-banded in the Nova Scotia study (see Miller 1977, 1979a). Display flights were timed with a stopwatch and were filmed with a super g-mm movie camera at 24 frames per second. Data on wind velocity were obtained from Environment Canada, Atmospheric Environment. Vocalizations on Sable Island were recorded at 19 cm/s using Scotch tape 176 and a Uher 4200 Report Stereo IC tape recorder, with a Uher M5 17 dynamic microphone mounted in a Dan Gibson parabolic reflector. All other

At temperatures below 28”C, rate of oxygen consumption (vjo2) of Zebra Finches (Poephila guttuta) incubating eggs averaged 20% higher than the \ioz of non-incubating Zebra Finches sitting in a nest at the same temperature. This increase represents the energetic cost of incubation. The O,, of non-incubating birds sitting in a nest was lower than values reported for birds perched in the open at the same temperature. In the Zebra Finch, the ameliorating effects of the nest microclimate approximately compensate for the increment in metabolic rate due to incubation. The energetic cost of incubation increased when birds had to rewarm cold eggs. Incubating birds responded to artificially cooled eggs by elevating their metabolic rate and increasing heat flow to the clutch. The pattern of adult attentiveness at the nest determines the number of times and amount by which the eggs must be rewarmed. Because it is energetically more expensive to rewarm eggs than to maintain temperature once the eggs are warm, the cost of incubation depends in part on the attentiveness pattern. Reproduction, especially the care of eggs and young, places special demands on the way birds allocate available energy. Various techniques have been used to estimate the energetic costs associated with territorial defense (Stiles 1971, Wolf and Hainsworth I971), nest building (Collias and Collias 1967, Withers 1977a), egg production (King 1973), and the feeding of nestlings (Utter and Lefebvre 1973). These activities, together with incubation of the eggs, include most of the time and energy that birds devote to reproductive activities. However, the costs of incubation, an activity that takes up a significant portion of the reproductive cycle, are difficult to measure and have been the subject of controversy (Kendeigh 1973, King 1973). Linear heat flow models have been used to make indirect estimates of the energetic cost of incubation based on the assumption that heat loss from eggs must be balanced by extra heat production by the parent (Kendeigh 1963, Ricklefs 1974). For example, Drent (1970) found that Kendeigh’ s (1963) model accurately described the heat input required to keep the eggs of Herring Gulls (Larus urgentu Mertens 1977) and Baird’ s Sandpiper, (Calidris hairi Norton 1973). However, neither author compared the oxygen consumption of incubating and non-incubating birds, and consequently it is impossible to estimate the energy expended solely for incubation. In contrast, Biebach (1977, 1979) measured the oxygen consumption of both incubating and non-incubating Starlings (Sturnus dgaris) and calculated the energetic cost of incubation at several nest temperatures. Gessaman and Findell (1979) measured CO, production of three incubating and non-incubating American Kestrels (F&o sparzjerius) but their results are ambiguous. Mertens (1980) measured heat loss from the nest of a Great Tit, using heat flux disks mounted in the nestbox walls, and found that heat loss from the bird and nest increased considerably during incubation. The energetic cost of warming cooled eggs “to the incubation temperature” has not been determined. Kendeigh et al. (1977) suggested that energy expended to rewarm eggs could be calculated from estimates of the heat needed to rewarm eggs, but this procedure ignores the inefficiency of heat transfer from the parent to the eggs. If a bird increases its heat production in order to re

A remarkable diversity of mating systems and related social behavior patterns is found in the sandpiper family Scolopacidae (including the Phalaropodinae, after Jehl, 1968). Mating systems range from territorial monogamy in the Willet (Cataptrophorus semipalmatus) (Vogt 1938), possible polygyny in the Pectoral Sandpiper (Calidris melanotos) (Pitelka 1959), polyandry in the Northern Phalarope (Phalaropus lobatus) (Raner 1972; Hilden and Vuolanto 1972) to lek promiscuity in the Ruff (Philomachus pugnax) (Hogan-Warburg 1966). In such species as the Pectoral Sandpiper (Pitelka 1959) and the Whiterumped Sandpiper (Calidris fuscicollis) (Parmelee et al. 1968), males play the active role in courtship and only females incubate, whereas the reverse is true in the phalaropes (Tinbergen 1935; H6hn 1967; Bengtson 1968). Between these extremes, other species exhibit varying degrees of role-sharing by the sexes. The strategy of pair formation in a given species probably represents a series of adaptations to a set of social and environmental conditions. Holmes and Pitelka (1966) have presented an ecological classification of social systems in calidridine sandpipers based upon the relative conservatism or opportunism in the manner of environmental exploitation. Their classification attempts to explain in particular the adaptiveness of spacing patterns of individuals during pair formation and the resulting monogamous, polygamous, or promiscuous mating system. In this paper the social phases of early pair formation in Wilson's Phalarope (Phalaropus tricolor) are examined in some detail with a view to interpreting the adaptiveness of the social behavior patterns exhibited. No attempt will be made at this stage to explain the reversal of sex roles, for which this species and its congeners are well known (Bent 1927). A later paper will deal with the interactions of the sexes during the subsequent period of avoidance of conspecifics, during which time the pair bond is completed and nesting initiated. This study follows and supplements earlier investigations into the breeding biology of W lson's Phalarope, most notably those of H6hn (1967) and Johns (1969). Names of taxa follow the classification of Jehl (1968).

Eggs of 10 species ofshorebirds (Charadriidae, Scolopacidae, Phalaropodinae) collected at Churchill, Manitoba, were measured and artificially incubated. Neonates were weighed within 6 h of hatching. This paper reports variation in egg size and neonate mass among clutches, and the relationship between egg dimensions and neonate mass. Coefficients of variation were 4 to 9% for egg volume and 6 to 15% for neonate mass. In most species, a significant proportion (48-84%) of the variance in egg volume could be attributed to differences between clutches. Neonate mass was significantly related to egg size in six of nine species. Coefficients of variation in the volume of eggs within populations of shorebirds (Charadriidae, Scolopacidae, and their allies) are on the order of 4 to 7% (Viisanen et al. 1972, Viisinen 1977). Much of this variation arises from differences in the sizes of eggs laid by different females, which are detected as between-clutch variation (e.g., Viis~nen et al. 1972, Miller 1979, Baker and Cadman 1980). The relationship between the sizes of eggs and neonates has been described for many species of birds, including some members of Charadriiformes (e.g., Ricklefs et al. 1978, Lundberg and Vdisinen 1979, Lloyd 1979), but not for shorebirds. Because shorebird chicks must feed themselves shortly after hatching, often in cold environments, larger size, more advanced developmental state, and greater energy reserves of neonates presumably carry a selective premium, all else being equal. Indeed, the relative egg size (percent adult mass) of shorebirds is large compared to most other groups of birds (Rahn et al. 1975). If egg size is under strong selection (i.e., most unfavorable genes have been removed), variation within populations must be either nongenetic in origin or compensated by variation in other, balancing traits that are correlated with egg size (e.g., Rose 1982). The large variance between clutches found in most populations suggests genetic variation in egg size, although age and developmental effects have not been ruled out. As a step towards understanding the evolution of large egg size in shorebirds, and interpreting variation in egg size among birds in general, I report here on variation in egg size and neonate mass among clutches, and on the relationship between egg size and neonate mass in 10 species of shorebirds at Churchill, Manitoba. MATERIALS AND METHODS Ten species were included in this study: Lesser Golden-Plover (Pluvialis dominica); Semipalmated Plover (Charadrius semipalmatus); Whimbrel (Numenius phaeopus); Hudsonian Godwit (Limosa haemastica); Lesser Yellowlegs (Tringaflavipes); Stilt Sandpiper (Calidris himantopus); Short-billed Dowitcher (Limnod us griseus); Dunlin (Calidris alpina); Least Sandpiper (C. minutilla); Red-necked Phalarope (Phalaropus lobatus). These were the speci s most readily available in the study area and, fortuitously, represent much of the variation in size and habits among arctic shorebirds. Clutches were collected at various stages of incubation from wet and dry tundra habitats to th east of Churchill, Manitoba (500N, 940W), during midand late June 1979. Eggs were marked with indelible ink and their lengths (L) and breadths (B) were measured to the nearest 0.1 mm with dial calipers. I used th product of the length and the square of breadth (LB2) as an index to volume (Viisanen 1969, Vdisanen et al. 1972). Regressions of volume on LB2 had coefficients of determination of between 88 and 98% in eight species of waders studied by VdtisAnen (1977). Eggs were incubated in a small incubator (Hovabator, Inc.) at 370C and approximately 60% rela ive humidity. Neonates were individually marked and weighed soon after hatching, usually within 6 h. I could match neonates to their eggs unambiguously in most cases. Where there was doubt, the data were omitted from the pertinent analyses. Additional data on lengths and breadths of eggs in 5 clutches of Hudsonian Godwits, 8 clutches of Whimbrels, 7 clutches of Shortbilled Dowitchers, 24 clutches of Least Sandpipers, and 33 clutches of Stilt Sandpipers (all from the Churchill area) were generously provided by J. R. Jehl. I analyzed these measurements separately, rather than pooling them with my data, because neonatal masses were not available. I used the SAS statistical package (Helwig and Council 1979), primarily the MEANS and GLM procedures, to analyze the data. Univariate statistics presented are the

We studied the nest attentiveness of six female White-rumped Sandpipers (Calidris fuscicollis), a species with uniparental care which incubates in the continuous daylight of the arctic summer. We used correlation and multiple regression analyses to determine how well day-to-day variation in recess time/day, number of trips/day, and average trip length/day could be explained by date, concurrent weather, behavior on the previous day, and weather on the previous day. Both previous and concurrent weather were important predictors of incubation behavior, while date and previous behavior were not. We therefore conclude that incubation behavior on a given day is not simply a function of current conditions. Behavior appears at least to integrate the effects of both present weather and weather on the previous day.