Monitoring populations of Western Sandpipers and Pacific Dunlins during northward migration on the Fraser River Delta,British Columbia, 1991–2013

The Fraser River Delta in British Columbia, Canada, is a globally significant stopover site for shorebirds, but the population status and trends of many species that use the site remain uncertain. We describe an ongoing program to monitor population trends of the two most abundant species, Western Sandpipers (Calidris mauri) and Dunlins (Calidris alpina), during northward migration. Counts of these species were conducted at a mudflat where large flocks assembled at mid‐tide from 15 April to 15 May, 1991–2013, and we estimated species‐specific counts as the product of daily total flock counts and species proportions obtained during supplementary sampling. The median peak count of both species combined was 177,000 birds, and occurred between 24 April and 3 May. Ratios (proportions) of the two species followed a predictable pattern during the migration period, with a low proportion of Western Sandpipers (3%–20%) in flocks before 20 April, followed by a rapid increase to 80%–100% between 25 April and 10 May and a variable decrease to 30%–80% by 15 May. Mean counts of Western Sandpipers showed no significant trend over the study period. Mean counts of Dunlins showed a non‐linear trend, decreasing until 2001 and then increasing to 2013. Bias and random error in field counts were quantified by comparing field counts to counts made from photographs taken during surveys, and analysis revealed that field counts had a downward, but predictable, bias, accounting for >90% of birds present, with a stochastic error rate of 28.0%. Uncertainty in total population estimates was high after accounting for the effect of length of stay and sampling error. Population estimates suggested that 600,000 Western Sandpipers and 200,000 Dunlins typically passed through the site during northward migration. Our estimates indicate the usefulness of daily counts at major stopover sites during northward migration as an effective tool for monitoring shorebird populations, and underscore the need for conserving such sites.     

Effects of leg flags on nest survival of four species of Arctic‐breeding shorebirds

Marking wild birds is an integral part of many field studies. However, if marks affect the vital rates or behavior of marked individuals, any conclusions reached by a study might be biased relative to the general population. Leg bands have rarely been found to have negative effects on birds and are frequently used to mark individuals. Leg flags, which are larger, heavier, and might produce more drag than bands, are commonly used on shorebirds and can help improve resighting rates. However, no one to date has assessed the possible effects of leg flags on the demographic performance of shorebirds. At seven sites in Arctic Alaska and western Canada, we marked individuals and monitored nest survival of four species of Arctic‐breeding shorebirds, including Semipalmated Sandpipers (Calidris pusilla), Western Sandpipers (C. mauri), Red‐necked Phalaropes (Phalaropus lobatus), and Red Phalaropes (P. fulicarius). We used a daily nest survival model in a Bayesian framework to test for effects of leg flags, relative to birds with only bands, on daily survival rates of 1952 nests. We found no evidence of a difference in nest survival between birds with flags and those with only bands. Our results suggest, therefore, that leg flags have little effect on the nest success of Arctic‐breeding sandpipers and phalaropes. Additional studies are needed, however, to evaluate the possible effects of flags on shorebirds that use other habitats and on survival rates of adults and chicks.     

A non‐lethal biopsy technique for sampling subcutaneous adipose tissue of small and medium‐sized birds

Analysis of fatty acids from adipose tissue can provide important information about the physiological and nutritional condition of birds. However, non‐lethal biopsy procedures and their potential negative effects on small and medium‐sized birds have not been adequately assessed. We developed a biopsy procedure for collecting small amounts of adipose tissue from the furcular area of small and medium‐sized birds (13–62 g) without adverse effects. The biopsy procedure was performed on Dunlins (Calidris alpina), a medium‐sized migratory shorebird, and small hybrid songbirds (European Goldfinch [Carduelis carduelis] × Atlantic Canary [Serinus canaria]). The biopsy involved making a skin incision 2–3 mm long on one side of the furcular region to collect 2–16 mg of adipose tissue. All birds were monitored for 2 weeks after biopsies to examine potential effects of the procedure on body mass, visible fat deposition, time for wound healing, hematocrit levels, total white blood cell counts, and heterophil:lymphocyte ratios. Visible scars were apparent for 10 d for hybrids and 6 d for Dunlins, with no evidence of infection or abnormal scar tissue formation. Body mass of songbirds did not differ before and after the biopsy, but Dunlins increased body mass and visible fat deposition after biopsy. The collection of adipose tissue in the furcular region was performed only for birds with fat scores ≥2, and the tissue collected never represented more than 0.07% of a bird's body mass; we recommend both these values to avoid any possible unknown negative effects. Our non‐lethal biopsy technique is relatively simple to perform, and we recommend it as an alternative to lethal methods for sampling adipose tissue in studies of wild and captive birds.     

Use of wetlands at the mouth of the Yangtze River by shorebirds during spring and fall migration

ABSTRACT.   The mouth of the Yangtze River is an important stopover site for migratory shorebirds using the East Asian-Australasian Flyway. From 1984 to 2004, we censused and banded shorebirds and monitored hunting activities at the mouth of the Yangtze River to understand how shorebirds used the study area. Counts and banding data revealed greater numbers of shorebirds at the mouth of the Yangtze River during northward migration (spring) than during southward migration (fall), with ratios varying from 1.5:1 to 7.2:1 at different sites from 1984 to 2005. The most common species observed during spring (northward) migration were Great Knots ( Calidris tenuirostris ), Red Knots ( Calidris canutus ), Bar-tailed Godwits ( Limosa lapponica ), Sharp-tailed Sandpipers ( Calidris acuminata ), and Red-necked Stints ( Calidris ruficollis ). During spring 2003–2004, 96.98% of the shorebirds observed were adults (ASY or older) and 3% were after hatching-year and second-year birds (AHY or SY). In contrast, almost all (94.73%) birds counted during the fall were hatching-year (HY) birds. These results indicate that adult shorebirds either use a different migration route during fall migration or use the same route, but do not stop at the mouth of the Yangtze River. HY birds, however, may depend on the coastal stopover sites for feeding during their first southward passage.     

Community composition and migration chronology of shorebirds using the saline lakes of the Southern Great Plains, USA

ABSTRACT.   Shorebirds migrating through the Southern Great Plains (SGP), USA, use freshwater playas and saline lakes as stopovers. The importance of playas is well documented, but the role of saline lakes is not clearly understood. During 2002 and 2003, we conducted surveys to determine the extent to which the saline lakes serve as stopovers. Twenty-eight species were recorded, and total seasonal abundance ranged from 6779 to 29,924 birds. Potential shorebird abundance for extant saline lakes was estimated at 37,000–71,000 shorebirds annually. American Avocets ( Recurvirostra americana ), Western Sandpipers ( Calidris mauri ), Baird's Sandpipers ( C. bairdi ), Least Sandpipers ( C. minutilla ), Snowy Plovers ( Charadrius alexandrinus ), Killdeer ( Charadrius vociferus ), and Wilson's Phalaropes ( Phalaropus tricolor ) were the most abundant species. Community composition of shorebirds differed between saline lakes and regional freshwater playas. Peak spring abundance was generally in April, whereas summer/fall migration was more protracted and shorebird abundance peaked during 6–8 weeks in August and September. Migration chronologies differed among morphologically similar species, and among representative species from different guilds. Such patterns of temporal separation permit partitioning of resources by shorebirds migrating through the SGP. The saline lakes of the SGP should be regarded as stopover sites of regional and international value. To ensure that saline lakes function as stopovers and to help maintain those unique communities that inhabit them, conservation of saline lakes should focus on preserving spring flows and conserving water.     

Density-dependent mortality of wintering Dunlins Calidris alpina through predation by Eurasian Sparrowhawks Accipiter nisus

Density-dependent mortality in wintering shorebirds is critical to shorebird population dynamics, but is difficult to study and demonstrate. Most winter mortality of small shorebirds probably results from predation by raptors. Over 13 winters, I studied Eurasian Sparrowhawk Accipiter nisus predation on wintering Dunlins Calidris alpina at a rocky shore in south-east Scotland, a site apparently of marginal suitability for wintering Dunlins. Most Dunlins on the study site were juveniles (first winter birds), and winter juvenile mortality rate due to Sparrowhawk predation was strongly and positively related to Dunlin density (maximum winter count). There was no indication of any marked effect of weather on Dunlin winter mortality rate, except that mortality was slightly greater in winters with lower temperatures. Dunlin mortality was unrelated to the mortality through Sparrowhawk predation of a preferred prey, the Redshank Tringa totanus , or to sighting rates of hawks, suggesting that increased hunting of Redshanks by hawks or a numerical response by hawks were not involved in density-dependent mortality of Dunlins.     

Spring migration dynamics and sex-specific patterns in stopover strategy in the Wood Sandpiper Tringa glareola

Due to being a virtually monomorphic wader species, migration dynamics and sex-related migration patterns in the Wood Sandpiper (Tringa glareola) have rarely been investigated. We captured spring migrants at an important stopover site in northeastern Austria. Birds were individually color-marked, and sex was determined by an analysis of DNA from tail feather material. Among temporary residents (birds seen again after day of capture), males migrated on average 3 days earlier than females. However, since sexes did not differ in fat score, the length of stay and the proportion of transients (birds not seen again after day of capture) and temporary residents, we suggest that males and females adopt similar migration strategies in the spring. The large number of transients captured as well as shorter stopover durations in later temporary residents indicate that Wood Sandpipers minimize time at this stage of their northbound migration. Temporary residents earlier in the season exhibited lower fat stores than later ones. Nevertheless, since the fat stores of transients and temporary residents were similar even after the progress of the season had been accounted for, we assume that Wood Sandpipers may afford to exhibit individual flexibility in migration strategy and the use of stopover sites, especially early in the season. This variability may be a necessary adaptation to cope with possible varying environmental conditions at dynamic and unpredictable inland stopover sites. After having reached North Mediterranean regions, mean body mass of spring migrants gradually increases during successive stopovers, indicating that Wood Sandpipers follow a ‘hopping’ migration strategy. This emphasizes the high conservation value of even small artificial mudflat pools as important stepping stones in order to maintain a continuous network of wetland habitats for this continental migrant.     

Oiling rates and condition indices of shorebirds on the northern Gulf of Mexico following the Deepwater Horizon oil spill

The coastline of the Gulf of Mexico in the United States is an important wintering and stopover region for migratory shorebirds. The Deepwater Horizon oil spill (April–August 2010) impacted more than 1700 km of this coastline and could potentially affect shorebirds through long‐term exposure to toxins, degraded habitats, and altered food chains. We investigated the exposure to Deepwater Horizon oil of seven species of shorebirds that winter or stopover along the northern Gulf of Mexico. From October 2010 to May 2012, we captured and banded 691 shorebirds at six sites that experienced varying levels of oil contamination. Of birds sampled, 22 were lightly oiled, with species that forage on the coast having higher rates of oiling than those that forage in more estuarine habitats. Although only 8.6% of birds captured from October 2010 to May 2011 and 0.6% of the birds captured from August 2011 to June 2012 showed signs of oiling, an unknown, but potentially larger, number of shorebirds were likely exposed to indirect effects of the spill, such as decreased foraging time due to oiling of sites or disturbance from cleanup activities. Fuel stores and fattening rates of Dunlins (Calidris alpina) during spring migration, as measured using plasma metabolites, were not influenced by site oiling level. However, the level of disturbance at study sites was a significant predictor of both fuel stores and glycerol levels, suggesting that Dunlins stopping over during spring migration may have had difficulty reaching necessary fuel stores in spring 2011 due to disturbance from cleanup activity on oiled beaches. These effects from disturbance were only observed at sites with high cleanup activity, suggesting that the impact of oil‐spill cleanup on shorebirds may be minimized by limiting cleanup activities to specific areas and times of day.     

Behavior of Buff-Breasted Sandpipers (Tryngites subruficollis) during Migratory Stopover in Agricultural Fields

Background

Understanding the behavior of birds in agricultural habitats can be the first step in evaluating the conservation implications of birds'' use of landscapes shaped by modern agriculture. The existence and magnitude of risk from agricultural practices and the quality of resources agricultural lands provide will be determined largely by how birds use these habitats. Buff-breasted Sandpipers (Tryngites subruficollis) are a species of conservation concern. During spring migration large numbers of Buff-breasted Sandpipers stopover in row crop fields in the Rainwater Basin region of Nebraska. We used behavioral observations as a first step in evaluating how Buff-breasted Sandpipers use crop fields during migratory stopover.

Methodology/Principal Findings

We measured behavior during migratory stopover using scan and focal individual sampling to determine how birds were using crop fields. Foraging was the most frequent behavior observed, but the intensity of foraging changed over the course of the day with a distinct mid-day low point. Relative to other migrating shorebirds, Buff-breasted Sandpipers spent a significant proportion of their time in social interactions including courtship displays.

Conclusions/Significance

Our results show that the primary use of upland agricultural fields by migrating Buff-breasted Sandpipers is foraging while wetlands are used for maintenance and resting. The importance of foraging in row crop fields suggests that both the quality of food resources available in fields and the possible risks from dietary exposure to agricultural chemicals will be important to consider when developing conservation plans for Buff-breasted Sandpipers migrating through the Great Plains.     

Aggressive behaviours and correlates of dominance in Purple Sandpipers Calidris maritima at a communal winter roost

Aggression and the competitive ability of individual Purple Sandpipers were studied at a communal winter roost in northeast England. Aggression was most intense in high winds and more frequent in moderate breezes than when wind speeds were high or low. Higher wind speeds resulted in a drop in aggression rate, as birds had to face into the wind to maintain their balance. The ability of an individual to secure a sheltered roost position was related to its size and sex, larger individuals being dominant over those smaller than themselves. Purple Sandpipers exhibit reversed sexual size dimorphism and females were thus dominant over males. There was also weak evidence that adults were dominant over first-winter birds. The importance of size and sex in determining dominance at the roost is discussed in relation to the evolution of reversed sexual size dimorphism in Purple Sandpipers and similar shorebirds.     

Bill length: a reliable method for sexing Purple Sandpipers

ABSTRACT.   Purple Sandpipers ( Calidris maritima ) are sexually dimorphic, with females larger than males. We tested the reliability of using bill length to sex individuals and estimate the sex ratio at a stopover site in Iceland in May 2003 and 2005. Feather samples from 65 of 324 captured birds were used for molecular sexing, and generalized linear models (GLMs) were used to discriminate the sexes from body measurements of the molecularly sexed birds. About 3% of the 324 individuals were misclassified by the Harding-Cassie method, and the proportion of males was 0.657 compared to 0.656 according to the best GLM. Our results showed that the reliability of determining the sex and sex ratio of Purple Sandpipers using a Harding-Cassie plot of bill length measurements was high, but that reliability was improved by including other variables in a GLM. The estimate of an uneven sex ratio in the population we studied was not due to a systematic error, and supports the conclusion of earlier studies that Purple Sandpipers exhibit an uneven sex ratio in favor of males.     

Migrant shorebird use of Akimiski Island, Nunavut: a sub-arctic staging site

Determining the importance of stopover and staging areas to migrating shorebirds (Aves: Charadriiformes) is essential if such habitats are to be successfully protected. Migration chronology, species composition, length of stay, body condition, and estimated total abundance of shorebirds during spring and fall migratory periods of 2008 and 2009 were documented on Akimiski Island, Nunavut, Canada. Fourteen shorebird species were observed during spring point counts and 18 during fall. Semipalmated (Calidris pusilla) and White-rumped (C. fuscicollis) Sandpipers comprised about 80?% of all individuals observed. A greater number of species and individuals were observed during fall than spring in both years. Radio-transmitters attached to juvenile Semipalmated and Least (C. minutilla) Sandpipers indicated highly variable lengths of stay ranging up to 26?days in both species (Semipalmated Sandpiper averaged 6.5?±?2.67?days, n?=?12; Least Sandpipers averaged 7.25?±?3.79?days, n?=?8). In 2009, Semipalmated Sandpipers captured and weighed later in the season were significantly heavier than those captured earlier suggesting that this species is refueling while on Akimiski Island. A fall migration seasonal density of 5,267 (2,193–8,341) shorebirds/km² was estimated given a residence probability (i.e., the probability of an individual being present in consecutive counts) of 0.906?±?0.181. Assuming similar habitat value and shorebird density, an extrapolation of the seasonal plot density of 5,267 birds/km² to the total 192?km² mudflat habitat on Akimiski Island yields an estimate of 1,011,264 (421,098–1,601,429) shorebirds during fall migration, making Akimiski Island of Hemispheric importance as a staging site for migrant arctic-breeding shorebirds.     

An evaluation of condition indices and predictive models for noninvasive estimates of lipid mass of migrating Common Yellowthroats, Ovenbirds, and Swainson's Thrushes

ABSTRACT.   Noninvasive methods of measuring lipid mass in birds are widely used, but not frequently evaluated. I evaluated the ability of three noninvasive indicators of fat content (fat scores, body mass, body mass/wing chord) and regression models to predict lipid mass in two migratory songbirds previously unexamined in this context—Common Yellowthroat ( Geothlypis trichas ) and Ovenbird ( Seiurus aurocapillus ). I also examined the accuracy of these methods for Swainson's Thrushes ( Catharus ustulatus ) for comparison to a previous study. Fat score, body mass, and body mass/wing chord were highly correlated with chemically extracted lipid mass in each species. In all three species, birds with no visible subcutaneous fat possessed considerable quantities of fat, ranging from 9.8 to 19.7% of total dry body mass. Forward-selected regression models explained 69−87% of lipid mass variation, with prediction errors of 14.6−27.5%. An existing predictive model for the Swainson's Thrush overestimated lipid mass by an average of 92%. Fat score, body mass, and the regression models generated here are reliable predictors of lipid mass in two of the three migrating species examined. The accuracy of the methods, in addition to their low cost and simplicity, justifies their continued use in field studies of birds.     

Crossbow‐netting: a new method for capturing shorebirds

Capturing shorebirds during the non‐breeding season can be challenging because they are usually scattered over wide‐open intertidal areas while foraging and are sensitive to human disturbance at roosts where they gather during high tide in large vigilant flocks. Several techniques are available for capturing shorebirds, but, for a study of stopover ecology, we needed a method that would allow us to capture Dunlins (Calidris alpina) on a regular basis at high‐tide roosts during the day (ruling out mist‐nets), did not require the use of gun‐powder (ruling out cannon‐nets), and that would deploy a net faster than clap nets, whoosh nets, and wilsternets. Therefore, we developed a new method to capture shorebirds where a crossbow is used to pull a mist‐net over flocks of roosting birds. We tested this technique in four habitats (saltpans, salt marshes, beaches, and mudflats) in the Tagus estuary, Portugal, and captured over 380 birds representing eight different species. Advantages of this technique compared to other methods (e.g., mist‐nets, clap‐ and whoosh nets, and cannon‐nets) include (1) portability, (2) ease of set up, (3) minimal disturbance of birds near the capture area, and (4) no explosive materials are needed. Our results suggest that crossbow‐netting is a safe and useful capture technique, especially for studies requiring the capture of small numbers of birds on a regular basis.     

鸡瘦蛋白受体(OBR)基因内含子8单核苷酸多态性与体脂性状的相关研究

以东北农业大学高低脂双向选择系的第 6世代肉鸡为材料 ,鸡 7周龄时测定体重和腹脂重等屠体性状。根据鸡瘦蛋白受体基因内含子 8的序列 (GenBank登陆号 :AF2 2 2 783 )设计引物 ,用直接测序的方法检测多态性位点 ,用PCR SSCP的方法进行基因型分析 ,建立适合的统计模型对多态性位点产生的基因型与生长和体组成性状进行相关分析。结果表明 ,在第 50 0和 659位碱基同时发生了T—C、G—A突变。经最小二乘分析 ,3种基因型在腹脂重和腹脂率上差异显著 (P <0 0 5) ,BB型个体腹脂重和腹脂率显著高于AB型 (P <0 0 5) ,极显著地高于AA型个体 (P <0 0 1) ;3种基因型在肝重上差异显著 (P <0 0 5) ,且AA基因型个体的肝重显著低于AB和BB基因型个体。初步推断OBR基因可能是影响鸡脂肪性状的主效基因或与主效基因连锁 ,推测可以利用这个多态位点对鸡的体脂性状进行标记辅助选择     

Using egg flotation and eggshell evidence to determine age and fate of Arctic shorebird nests

ABSTRACT.   Egg flotation was used to estimate incubation age and eggshell evidence was collected to determine nest fate at nests of 11 species of shorebirds on the Arctic Coastal Plain of Alaska during 2002–2004. We present egg-flotation schedules for nine species to facilitate the estimation of nest age. We evaluated the predictive ability of an egg-flotation schedule for Semipalmated Sandpipers ( Calidris pusilla ) and were able to estimate incubation age within ∼1–3 d of the assumed age. Patterns of eggshell evidence were similar across species, with eggshell fragments (1–5 mm) present at most successful nests (96%) and eggshell tops or bottoms present only at successful nests. We determined nest fate independently of eggshell evidence and then used discriminant function analysis to predict the probability of correctly classifying a nest's fate using different types of eggshell evidence. The use of eggshell fragment evidence resulted in the correct classification of the fate of all 11 species of shorebirds in 92% of the cases. Both the egg-flotation technique and eggshell evidence can be used in future studies to calculate accurate measures of reproductive success needed for ecological investigations of shorebirds.     

Age structure and age‐related differences in molt status and fuel deposition of Dunlins during the nonbreeding season at Chongming Dongtan in east China

ABSTRACT Although most shorebirds exhibit deferred migration and deferred breeding during their first summer, Dunlins (Calidris alpina) migrate to breeding areas and breed during their first summer. First‐year and adult Dunlins should, therefore, have similar fueling and molt patterns if energetic and physiological constraints are responsible for deferred migration. From 2006 to 2008, we examined the age structure of Dunlins during the nonbreeding season at Chongming Dongtan, an estuarine wetland in the Yangtze River estuary in east China, and examined the effects of date, age, and molt status on fuel deposition during migration and during the winter. The Dunlin population at Chongming Dongtan was composed primarily of first‐year birds. Most adults and first‐year birds arrived together in late August. Regression analyses indicated that age, date, and molt status affected fuel deposition (as indicated by body mass) of Dunlins. Adults had significantly greater fuel deposits than first‐year Dunlins near the end of northward migration (May: adults 70.8 ± 6.4 g, first‐year 63.8 ± 8.0 g) and at the start of southward migration (September: adults 50.2 ± 6.1 g, first‐year 47.2 ± 4.9 g). Adults also had significantly higher fuel deposition rates than first‐year Dunlins during northward migration. Nonetheless, first‐year Dunlins migrate and breed in their first summer. Thus, other factors, such as migration distance and body size, may be more important in determining if first‐year shorebirds defer migration during their first spring and summer. During boreal spring and autumn, first‐year Dunlins in active body molt had greater body mass than those that had not initiated body molt or those in suspended molt, and premigratory fuel deposits for northward migration were greatest after prealternate molt was completed. These results suggest that body molt requires additional fuel deposits and imposes a constraint on fuel deposition for migratory flights.     

Territorial behavior of Western Sandpipers on their nonbreeding grounds: effect of sex and foraging interference

ABSTRACT Nonbreeding shorebirds often alternate social structure between anonymous flocks and territorial behavior in response to different environmental factors. To evaluate specific drivers for one species, we studied the spacing behavior of wintering Western Sandpipers (Calidris mauri) at Bahía Santa María, northwestern Mexico, using behavioral observations. The density, population structure, and territorial behavior of Western Sandpipers differed among three habitat types. Cattail marshes supported 110 birds per ha, 49% males, and no territorial birds. Mangrove flats supported 288 birds per ha, 58% males, and 5% territorial birds. Brackish flats supported 365 birds per ha, 76% males, and 7% territorial birds. Territories consisted of rectangular strips (5–9 m long, N= 77). Territory length was not related to either bird density or number of territorial birds by plot, but was positively related to nearest bird distance. Aggression rate was inversely related to territory length, suggesting that territory length is set by the costs of defense. Foraging rate was independent of territory length, and prey densities in territories did not differ from those in areas used by nonterritorial birds. Males were more likely to be territorial and had a higher aggression rate than females, suggesting that males, which forage more on surface prey, were more affected by foraging interference. Our results suggest that the territorial behavior of Western Sandpipers in our study was an opportunistic strategy to reduce foraging interference. The variation in spacing behavior we documented provides evidence that interference competition affects the social structure of Western Sandpipers during the nonbreeding season.     

Energetic solutions of Rock Sandpipers to harsh winter conditions rely on prey quality

Rock Sandpipers Calidris ptilocnemis have the most northerly non‐breeding distribution of any shorebird in the Pacific Basin (upper Cook Inlet, Alaska; 61°N, 151°W). In terms of freezing temperatures, persistent winds and pervasive ice, this site is the harshest used by shorebirds during winter. We integrated physiological, metabolic, behavioural and environmental aspects of the non‐breeding ecology of Rock Sandpipers at the northern extent of their range to determine the relative importance of these factors in facilitating their unique non‐breeding ecology. Not surprisingly, estimated daily energetic demands were greatest during January, the coldest period of winter. These estimates were greatest for foraging birds, and exceeded basal metabolic rates by a factor of 6.5, a scope of increase that approaches the maximum sustained rate of energetic output by shorebirds during periods of migration, but far exceeds these periods in duration. We assessed the quality of their primary prey, the bivalve Macoma balthica, to determine the daily foraging duration required by Rock Sandpipers to satisfy such energetic demands. Based on size‐specific estimates of M. balthica quality, Rock Sandpipers require over 13 h/day of foraging time in upper Cook Inlet in January, even when feeding on the highest quality prey. This range approaches the average daily duration of mudflat availability in this region (c. 18 h), a maximum value that annually decreases due to the accumulation of shore‐fast ice. Rock Sandpipers are likely to maximize access to foraging sites by following the exposure of ice‐free mudflats across the upper Cook Inlet region and by selecting smaller, higher quality M. balthica to minimize foraging times. Ultimately, this unusual non‐breeding ecology relies on the high quality of their prey resources. Compared with other sites across their range, M. balthica from upper Cook Inlet have relatively light shells, potentially the result of the region's depauperate invertebrate predator community. Given the delicate balance between environmental and prey conditions that currently make Cook Inlet a viable wintering area for Rock Sandpipers, small variations in these variables may affect the suitability of the site in the future.     

基于形态特征判定五种鹬类性别的可靠性

快速准确地鉴定两性同型鸟类个体性别在鸟类生态学研究中具有重要意义。本文选择2008年春季迁徙期在崇明东滩停歇的大滨鹬(Calidris tenuirostris)、红腹滨鹬(C.canutus)、红颈滨鹬(C.ruficollis)、尖尾滨鹬(C.acuminata)及翘嘴鹬(Xenus cinereus)5种两性同型的鹬类,用分子生物学方法进行性别鉴定,并基于个体的形态特征(体重、翅长、喙长、头喙长及跗跖长)采用判别分析方法对性别进行判定。结果表明,尖尾滨鹬雄性各形态特征均显著大于雌性,其他4种鹬类则相反。5种鹬类形态特征的性别差异指数在0.5%~25.3%之间,重叠度在29.4%~98.6%之间。5种鹬类判别分析判定性别的准确率在(0.69±0.06)~(0.96±0.01)之间,其中,尖尾滨鹬判别准确率(0.96)最高,翘嘴鹬判别准确率(0.69)最低。形态特征在两性间的差异程度影响性别的判别准确率。另外,两性性比对性别判别的准确率也有影响:性比偏雄性鸟类的雄性判别准确率高于雌性,而性比偏雌性鸟类的雌性判别准确率高于雄性。采用判别分析估测的性比与分子生物学鉴定结果相似,表明判别分析在判定种群的性比方面具有较高的可靠性。