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Many migratory shorebird species using the East Asian–Australasian Flyway are declining rapidly. While the loss of staging habitats in East Asia is considered the primary cause, stressors to fitness often occur throughout the geographic range of declining species, and threats in the non-breeding grounds have been comparatively poorly studied. Three species of migratory shorebird, Curlew Sandpiper (Calidris ferruginea), Sharp-tailed Sandpiper (C. acuminata) and Red-necked Stint (C. ruficollis), use Australia’s dynamic temporary wetland systems opportunistically, yet these large wetland systems have become increasingly degraded, with reduced frequency and extent of flooding. Here, we test whether variables related to wetland availability in Australia’s interior can explain annual variation in apparent survival, abundance or immature to adult ratios at three well-monitored coastal shorebird areas in southern Australia (total area > 1315 km2). We show that coastal annual bird abundance and ratios of immatures at the coast were higher when inland Australia was relatively hot and dry. Also, a small but significant amount of variation in annual apparent survival can be explained by annual variation in inland conditions, with higher survival rates in years when inland conditions were relatively wet and cool. For the endangered Curlew Sandpiper, the impacts of Australian environmental conditions may be exacerbating the impacts of conditions experienced in other parts of its range on fitness and survival. While the effects we document here are relatively weak, they do suggest that management of inland wetlands for these shorebirds may positively affect survival rates of these sharply declining species.

Vanausdall RA, Dinsmore SJ. 2021. Stopover ecology of the least sandpiper (Calidris minutilla) in Iowa: implications for reservoir management. Lake Reserv Manage. 37:300–312.Multipurpose reservoirs...

SummaryMigratory species rely on several distant sites during the annual cycle which makes their conservation more complex than that of non-migratory species. Even one of the most extensively studied migratory shorebirds - the Red Knot Calidris canutus - is currently ‘Near Threatened’ at the global level. Conflicting observations of migratory routes cast uncertainty on the subspecies classification and migratory connectivity of Red Knots in the Pacific coasts of the Americas. To fill essential information gaps, we present the first detailed population morphometrics of Red Knots during the non-breeding season in the southern Pacific coast, along with resightings of these birds throughout the Americas. We also estimated daily rate of weight gain during fuelling based on body mass at captures and known departure dates. Resightings demonstrate reliance on staging areas in both the Mid-continental and Atlantic flyways during the northward migration, and additionally in the Pacific Flyway during southward migration. In addition to the strong connection with several areas also used by C. c. rufa on the North American Atlantic coast, our results show morphometric differences within the ranges of both C. c. rufa and C. c. roselaari. Given the threats faced by Red Knots, the population in Chiloé Archipelago should be treated as a separate conservation unit within interhemispheric conservation programmes for endangered shorebirds within the Americas.

Dietary specialization is common in animals and has important implications for individual fitness, inter‐ and intraspecific competition, and the adaptive potential of a species. Diet composition can be influenced by age‐ and sex‐related factors including an individual's morphology, social status, and acquired skills; however, specialization may only be necessary when competition is intensified by high population densities or increased energetic demands.To better understand the role of age‐ and sex‐related dietary specialization in facilitating seasonal resource partitioning, we inferred the contribution of biofilm, microphytobenthos, and benthic invertebrates to the diets of western sandpipers (Calidris mauri) from different demographic groups during mid‐winter (January/February) and at the onset of the breeding migration (April) using stable isotope mixing models. Western sandpipers are sexually dimorphic with females having significantly greater body mass and bill length than males.Diet composition differed between seasons and among demographic groups. In winter, prey consumption was similar among demographic groups, but, in spring, diet composition differed with bill length and body mass explaining 31% of the total variation in diet composition. Epifaunal invertebrates made up a greater proportion of the diet in males which had lesser mass and shorter bills than females. Consumption of Polychaeta increased with increasing bill length and was greatest in adult females. In contrast, consumption of microphytobenthos, thought to be an important food source for migrating sandpipers, increased with decreasing bill length and was greatest in juvenile males.Our results provide the first evidence that age‐ and sex‐related dietary specialization in western sandpipers facilitate seasonal resource partitioning that could reduce competition during spring at the onset of the breeding migration.Our study underscores the importance of examining resource partitioning throughout the annual cycle to inform fitness and demographic models and facilitate conservation efforts., Our results provide the first evidence of seasonal differences in diet composition among demographic groups of western sandpipers, supporting the conclusion that age‐ and sex‐related dietary specialization facilitate seasonal resource partitioning in this species. Differences in diet composition among demographic groups were more pronounced at the onset of migration in spring compared to mid‐winter following the expectation that the consumption of biofilm and microphytobenthos provides energy for sandpipers during their breeding migration and reduces competition when high densities of birds occupy foraging sites. In spring, juveniles, particularly juvenile males, consumed more biofilm and microphytobenthos than adults supporting our hypothesis that sandpipers with shorter bills, lesser mass, and less prey handling experience would consume the greatest amount of biofilm and microphytobenthos. Photo credit: William Chan.

SummaryThe extent of intertidal flats in the Yellow Sea region has declined significantly in the past few decades, resulting in severe population declines in several waterbird species. The Yellow Sea region holds the primary stopover sites for many shorebirds during their migration to and from northern breeding grounds. However, the functional roles of these sites in shorebirds’ stopover ecology remain poorly understood. Through field surveys between July and November 2015, we investigated the stopover and moult schedules of migratory shorebirds along the southern Jiangsu coast, eastern China during their southbound migration, with a focus on the ‘Critically Endangered’ Spoon-billed Sandpiper Calidris pygmaea and ‘Endangered’ Nordmann’s Greenshank Tringa guttifer. Long-term count data indicate that both species regularly occur in globally important number in southern Jiangsu coast, constituting 16.67–49.34% and 64.0–80.67% of their global population estimates respectively, and it is highly likely that most adults undergo their primary moult during this southbound migration stopover. Our results show that Spoon-billed Sandpiper and Nordmann’s Greenshank staged for an extended period of time (66 and 84 days, respectively) to complete their primary moult. On average, Spoon-billed Sandpipers and Nordmann’s Greenshanks started moulting primary feathers on 8 August ± 4.52 and 27 July ± 1.56 days respectively, and their moult durations were 72.58 ± 9.08 and 65.09 ± 2.40 days. In addition, some individuals of several other shorebird species including the ‘Endangered’ Great Knot Calidris tenuirostris, ‘Near Threatened’ Bar-tailed Godwit Limosa lapponica, ‘Near Threatened’ Eurasian Curlew Numenius arquata and Greater Sand Plover Charadrius leschenaultii also underwent primary moult. Our work highlights the importance of the southern Jiangsu region as the primary moulting ground for these species, reinforcing that conservation of shorebird habitat including both intertidal flats and supratidal roosting sites in this region is critical to safeguard the future of some highly threatened shorebird species.

Migratory shorebirds show highly organized seasonal cycles in physiological and morphological traits (body mass and composition, plumage, hormone levels, etc.), which in captivity is accompanied by restless behaviour at times when free‐living birds would start migration. We introduce the idea that seasonally changing preference for habitat could motivate migrants to embark on migration and that this cognitive process could also guide them to seasonally appropriate places. We explored this by testing whether red knots (Calidris canutus), which also in captivity maintain marked circannual phenotypic rhythms, show evidence of seasonal change in preference for pictures of seasonally appropriate habitats. We first developed a method to verify whether red knots are able to memorize and discriminate contrasting pictures projected by LCD projectors. This was followed by two different experiments in which we tested for a seasonally changing preference for breeding or non‐breeding habitat. When carried out during the pre‐breeding season, the red knots are expected to prefer pictures of mudflats, their non‐breeding habitat. At the start of the breeding season, they should prefer pictures of the tundra breeding habitat. We established that knots are able to distinguish and memorize projected images. We failed to demonstrate the predicted change in vision‐based habitat preference, but for reasons of test design we do not interpret this as a strong rejection of the hypothesis. Instead, we suggest that experiments with greater numbers of individuals tested once, perhaps in combination with the provision of additional cues such as smells and sounds, will help the development of these ideas further.

The gut microbiota of birds is known to be characterized for different species, although it may change with feeding items. In this study, we compared the gut microbiota of birds with different feeding behaviors in the same habitat. We collected fecal samples from three Arctic species, snow buntings Plectrophenax nivalis, sanderlings Calidris alba, and pink‐footed geese Anser brachyrhynchus that are phylogenetically quite distant in different families to evaluate effects of diet on gut microbiota. Also, we characterized the prevalence of fecal bacteria using the Illumina MiSeq platform to sequence bacterial 16S rRNA genes. Our NMDS results showed that fecal bacteria of snow buntings and sanderlings were significantly distant from those of pink‐footed geese. Although all three birds were occupied by three bacterial phyla, Proteobacteria, Firmicutes, and Bacteroidetes, dominant taxa still varied among the species. Our bacterial sequences showed that snow buntings and sanderlings were dominated by Firmicutes and Bacteroidetes, while pink‐footed geese were dominated by Proteobacteria. In addition, the bacterial diversity in snow buntings and sanderlings was significantly higher than that in pink‐footed geese. Our results suggest that insectivorous feeding diet of snow buntings and sanderlings could be responsible for the similar bacterial communities between the two species despite the distant phylogenetic relationship. The distinctive bacterial community in pink‐footed geese was discussed to be related with their herbivorous diet., We showed that fecal bacteria of snow buntings and sanderlings were distant from those of pink‐footed geese. In addition, the bacterial diversity in snow buntings and sanderlings was significantly higher than that in geese. Our results suggest that diet as well as host phylogeny may affect the gut microbiota of Arctic birds.

n Focus: Reneerkens, J., Versluijs, T. S. L., Piersma, T., Alves, J. A., Boorman, M., Corse, C., ... Lok, T. (2020). Low fitness at low latitudes: wintering in the tropics in-creases migratory delays and mortality rates in an Arctic breeding shorebird. Journal of Animal Ecology, 89, 691–703. A central question in migratory ecology has been to understand the fitness consequences of individual variation in migration distance among different species and populations. Reneerkens et al. (2020) investigated the demographic consequences of long-distance migration for Sanderlings Calidris alba, an Arctic-breeding species of sandpiper. Their study population has a remark-able geographic distribution with a breeding range that is concentrated in north-east Greenland and Ellesmere Island, Canada but a nonbreeding range that extends across 85° of latitude from Scotland to Namibia. The authors report on unexpected patterns of latitudinal variation in three demographic parameters: timing of passage on northward migration, probability of juvenile migration and apparent survival of adults. Sanderlings travelling 1,800–2,800 km to settle at north temperate sites dur-ing the nonbreeding season had earlier passage dates, and also higher probabilities of migration and apparent survival. In contrast, birds travelling 6,000–7,800 km to equato-rial sites experienced later passage dates, delayed maturity and lower apparent survival. However, if Sanderlings migrated even farther and flew over 11,000 km to nonbreed-ing sites in Namibia, then their performance was restored to early passage dates and higher survival. Movement tracks from birds tagged with geolocators showed that birds wintering in Namibia make nonstop flights of 7,500 km that bypass West Africa during northward migration. Thus, all lines of evidence suggest that Sanderlings face adversity when spending the nonbreeding season at equatorial latitudes. Moreover, the central finding that components of fitness can have nonlinear relationships with migration dis-tance is a novel discovery that leads to many additional questions. The new findings have broader implications for theoretical models of migration, and for understanding how different patterns of movements may arise or be maintained in migratory species

Estuaries have historically been subject to considerable habitat loss, and continue to be subjected to such in areas where the natural landward migration of intertidal habitats is constrained by hard coastal defences. Thus, in estuaries where direct (e.g., port development) or indirect (e.g., sea level rise) processes are predicted to threaten intertidal habitats and associated waterbird species, there is a regulatory requirement to produce compensatory intertidal habitats. Managed realignment (MR) is a shoreline management practise that is undertaken to build sustainable coastal defences and create intertidal habitats in estuaries. This nature-based solution brings multiple benefits in the form of carbon storage, increased resilience to flooding, and, potentially, the formation of new habitats, which is the topic of this study. A 75-ha site at the Paull Holme Strays (Humber Estuary, United Kingdom) was monitored over a 10-year period following MR to examine the change in the abundance of waterbirds in the chosen site in response to the physical processes occurring there. Using digital terrain models (DTMs) collected via light detection and ranging (LiDAR), we examined how four compensatory target species responded to changes in elevation after the creation of the site. It was shown that the very rapid accretion of estuarine sediment occurred in the first decade of the new re-created intertidal, which, over time, led to changes in the numbers of benthic foraging birds supported. Furthermore, elevation change was also driven by this sediment accretion, the rate of which depended on the initial bed elevation of the sectors within the site. Ten years after the recreation of the habitat, the spatial heterogeneity in the bed elevation remained high; however, the sectors with the lowest elevations accreted the most over the 10-year period. The foraging number of the four waterbird species that colonised the MR site significantly declined above a certain elevation, with this effect being most pronounced for the Eurasian curlew (Numenius arquata). The number of common shelducks (Tadorna tadorna), dunlins (Calidris alpina), and common redshanks (Tringa totanus) declined significantly after initial peaks 5–7 years after the creation of the site, reflecting the ongoing elevation changes. Thus, this study highlighted the need for long-term studies to understand how species respond to large-scale habitat construction. It can also aid in predicting the suitability of an MR site for waterbirds in the medium and long term.

1. Animals exhibit varied life-history traits that reflect adaptive responses to their environments. For Arctic-breeding birds, traits like foraging guild, egg nutrient allocation, clutch size, and chick growth are predicted to be under increasing selection pressure due to rapid climate change and increasing environmental variability across high-latitude regions. 2. We compared four migratory birds (black brant [Branta bernicla nigricans], lesser snow geese [Chen caerulescens caerulescens], semipalmated sandpipers [Calidris pusilla], and Lapland longspurs [Calcarius lapponicus]) with varied life histories at an Arctic site in Alaska, USA, to understand how life-history traits help moderate environmental variability across different phases of the reproductive cycle. 3. We monitored aspects of reproductive performance related to the timing of breeding, reproductive investment, and chick growth from 2011–2018. 4. In response to early snow melt and warm temperatures, semipalmated sandpipers advanced their site arrival and bred in higher numbers, while brant and snow geese increased clutch sizes; all four species advanced their nest initiation dates. During chick rearing, longspur chicks were relatively resilient to environmental variation whereas warmer temperatures increased the growth rates of sandpiper chicks but reduced growth rates of snow goose goslings. These responses generally aligned with traits along the capital-income spectrum of nutrient acquisition and altricial-precocial modes of chick growth. Under a warming climate, the ability to mobilize endogenous reserves likely provides geese with relative flexibility to adjust the timing of breeding and the size of clutches. Warmer temperatures, however, may negatively affect the quality of herbaceous foods and slow gosling growth. 5. Species may possess traits that are beneficial during one phase of the reproductive cycle and others that may be detrimental at another phase, uneven responses that may be amplified with future climate warming. These results underscore the need to consider multiple phases of the reproductive cycle when assessing the effects of environmental variability on Arctic-breeding birds.

Cuba is the largest Caribbean island, supporting the most extensive wetlands in the region. Of the ~370 bird species in this country, approximately 40% are wetland-dependent and most are migratory. Knowledge of bird use of Cuba’s wetlands is critical for regional conservation. This study characterized waterbird assemblages in Cuban south coastal wetlands, reports spatio-temporal variations in waterbird diversity and suggests conservation strategies. We conducted 543 surveys across six wetlands (2011–2013). We recorded 110 species. Blue-winged Teal (Spatula discors) and Least Sandpiper (Calidris minutilla) were the dominant species. The site with the highest richness and waterbird abundance was Humedal Sur de Los Palacios. Differences in waterbird composition were identified among sites and seasons but not among years. No differences were found in spatial or temporal variability in abundance among sites, seasons or years. Assemblage composition was not spatially dependent on the location of wetlands. Twelve species were at abundance levels exceeding 1% of their estimated global population. This study highlights the global importance of the Cuban south coast to waterbird conservation, particularly during fall migration and the uniqueness of Humedal Sur de Los Palacios. We encourage creation of new Ramsar sites, an Important Bird Area and a new protected area.

Anthropogenic impact on nesting waders and passerine birds in the Arctic in surroundings of the industrial complex Sabetta, Yamal Peninsula, Russia was studied. A lot of factors associated with human development may affect nesting birds. The human-subsidized predation is considered to be the most significant. Anthropogenic food sources are usually present in human-transformed habitats, as well as additional dens and perch sites. This leads to a higher press of predation. In Sabetta, there are specific conditions causing artificially-limited predation and human-induced disturbance. Finding a large number of nests in close proximity to industrial infrastructure we have suggested that waders (order Charadriiformes) and passerine (order Passeriformes) birds may be tolerant to an urbanized landscape. In the studied industrial habitat, they probably do not reduce the nesting density, thanks to particular advantages of such habitats (drainability and variety of shelters). To test this hypothesis, we performed an analysis of the relationship between the nesting density of the 8 most abundant species of waders and passerines in relation to the degree of habitat transformation. Statistical analysis was carried out using the GLM module of Statsoft Statistica 10. We found a positive relation between nesting density of the Ringed Plover ( Charadrius hiaticula ) and Snow bunting ( Plectrophenax nivalis ) and the degree of transformation. Habitat transformation did not significantly affect the White wagtail ( Motacilla alba ) and Red-throated pipit ( Anthus cervinus ). The Lapland longspur ( Calcarius lapponicus ) showed a clear decrease of the nest density in transformed habitats. Last but not least, the Little stint ( Calidris minuta ), Temminck’s stint ( C. temminckii ) and Red-necked phalarope ( Phalaropus lobatus ) completely ignored only artificial habitats, whereas in partially transformed habitats, their mean nesting density was similar to undisturbed natural areas.

The red knot Calidris canutus, a flagship migratory waterbird species, continues to decline within the Americas. One major unanswered question is the status and connectivity of birds spending the non‐breeding season on the southern Pacific coast of South America. Answering this question will provide a useful geographic endpoint that could enhance ongoing conservation efforts. Red knots on Chiloe Island (43°S, Chile) were studied during four consecutive non‐breeding seasons (2014–2018) using systematic counts and resightings of ringed individuals in two shallow bays with known aggregations of other shorebird species. Maximum seasonal abundances (±SD) at each bay (68.8 ± 13.4; 85.0 ± 13.2) were similar across years. However, actual abundance on Chiloe is probably higher, as other suitable habitats were not surveyed. A total of 55 resightings corresponding to 14 individuals were recorded. The majority (72%) was for birds present during consecutive seasons; there were no recorded interchanges between bays. All birds, but one in Argentina, were ringed on the Atlantic coast of the USA (mainly the Gulf of Mexico) during their spring (northward) migration. Mark–resight data reveal a strong migratory connectivity between the southern Pacific coast of South America and the Atlantic coast of North America for this small but regular population of a highly imperilled species. Data also suggest that the red knots on Chiloe might be considered a separate conservation unit (most likely subspecies rufa). Thus, there is an urgent need to conduct comprehensive studies on Chiloe Island for the conservation of the intraspecific diversity of this migratory flagship species.

SummaryThe natural coastal wetlands of the East Asian-Australasian Flyway (EAAF) are disappearing at alarming rates, leading to rapid declines of many populations of waterbirds in the most species-rich flyway in the world. The identification and assessment of possible alternative habitats that may buffer the loss of natural wetlands should, therefore, be a priority for the conservation of migratory waterbirds using this flyway. Coastal saltpans are functional wetlands that support large numbers of waterbirds worldwide. The Nanpu Saltpans in the northern Bohai Bay of the Yellow Sea in China are one of the largest (290 km2) saltpan complexes in the world. In this paper, we document the value of the Nanpu Saltpans for supporting waterbirds. The surveys, carried out from 2013 to 2016, included waterbird counts in the saltpans (93 km2) at high and low tide and on the adjacent natural tidal flats (57 km2) at low tide. Of the 89 waterbird species recorded, 27 had maximum counts exceeding the 1% threshold value of estimated flyway populations. The maximum counts of waterbirds in northward migration and southward migration in the Nanpu Saltpans were 96,000 and 93,500, respectively, including both foraging and roosting birds; these figures do not account for turnover, so the total number of birds using the site is likely to be higher. The maximum counts on the adjacent tidal flats at low tide amounted to 73,000 and 20,000 waterbirds during northward and southward migration, respectively, and most of them were foraging birds. In the boreal winter, few birds fed in the saltpans, but several thousand fed on the tidal flats. Waterbirds used the inland ponds (2.0–18.0 km from the intertidal area) mainly for feeding both during low tide and high tide and used the nearshore ponds (0.3–4.3 km from the intertidal area) mainly for high-tide roosting. Some species, such as Black-tailed Godwit Limosa limosa, Marsh Sandpiper Tringa stagnatilis, Pied Avocet Recurvirostra avosetta, and Black-winged Stilt Himantopus himantopus, occurred mainly in the saltpans; other species preferred tidal flats, such as Red Knot Calidris canutus, Great Knot Calidris tenuirostris, Bar-tailed Godwit Limosa lapponica, Eurasian Curlew Numenius arquata, Relict Gull Larus relictus, and Grey Plover Pluvialis squatarola. This study clearly demonstrates the joint ecological function of the Nanpu Saltpan complex and adjacent tidal flats as a key staging area for waterbirds in the EAAF, and as such both urgently warrant protected status.

Estuaries of major rivers provide important stopover habitat for migratory birds throughout the world. These estuaries experience large amounts of freshwater inputs from spring runoff. Understanding how freshwater inputs affect food supply for migrating birds, and how birds respond to these changes will be essential for effective conservation of critical estuarine habitats. We estimated trends over time in counts of Western Sandpiper (Calidris mauri) and Pacific Dunlin (Calidris alpina pacifica) during northward migration on the Fraser River estuary, British Columbia, Canada, where shorebirds feed extensively on intertidal biofilm and invertebrates. We also examined whether counts were correlated with a suite of environmental variables related to local conditions (precipitation, temperature, wind speed and direction, solar radiation, tidal amplitude, and discharge rates from the Fraser River) during a total of 540 surveys from 1991 to 2019. Counts of Western Sandpiper declined ~54% (−2.0% per annum) over the entire study period, and 23% from 2009 to 2019 (−0.9% per annum). Counts of Pacific Dunlin did not show a statistically significant change over the study period. Counts of shorebirds were lower when discharge from the Fraser River was high, which we propose results from a complex interaction between the abrupt changes in salinity and the estuarine food web related to the quantity or quality of intertidal biofilm. Counts were also higher when tidal amplitude was lower (neap tides), potentially related to longer exposure times of the mudflats than during spring tides. Effects of wind are likely related to birds delaying departure from the stopover site during unfavorable wind conditions. The negative trend in migrating Western Sandpipers is consistent with declines in nonbreeding areas as observed in Christmas Bird Counts. Understanding causes of population change in migratory shorebirds highlights the need for research on mechanistic pathways in which freshwater inputs affect food resources at estuarine stopovers., Shorebird counts at a critical coastal stopover site have declined over a 29 year period (1991–2019). Counts were correlated with tidal amplitude, wind, and river discharge. We hypothesize a complex interaction between the abrupt changes in salinity from freshwater inputs, a decrease in quality and quantity of intertidal biofilm, and shorebird counts.

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.

Ecosystem functioning and services have provided a rationale for conservation over the past decades. Intertidal muddy sediments perform crucial functions, including erosion protection, nutrient cycling and carbon sequestration. Key mediators within this system include microphytobenthic biofilms, which bind sediment and influence nutrient biogeochemistry, and wading birds which feed extensively on sediment dwelling infauna, which in turn graze biofilms. Some wader species, specifically small sandpipers, have recently been found to interact directly with biofilms, e.g. by grazing, adding complexity to this food web. It has been suggested that infauna grazing by waders may lead to a reduction in biofilm grazing pressure by infauna. If this was the case it would likely have significant top-down, trophic cascade effects on key mudflat ecosystem functions. We carried out an exclusion experiment on the Colne Estuary, Essex, UK to examine whether wader presence significantly affects sediment erodibility, microphytobenthos fluorescence (Fo) and sediment-water nutrient fluxes (nitrate, nitrite, ammonia, phosphate and dissolved organic carbon (DOC)). Excluding wading birds caused significant changes in regulating and provisioning ecosystem functions, including mudflat erodibility and nutrient fluxes (with the exception of DOC). Fo was significantly greater, sediment critical shear strength increased, and the magnitude of nutrient fluxes increased where waders were absent. Excluding waders did not cause a significant difference in infauna density within the sediment, suggesting that a trophic cascade was not the cause of the measured effects. The dominant wading species at the site, dunlin Calidris alpina, is reported to consume biofilm and is considered to play a key role in maintenance of ecosystem stability on mudflats. After a period of 23 days, the arrival of the mud snail Peringia ulvae appeared to compensate for the absence of waders, consuming biofilm and causing a reduction in surface biofilm differences between presence/absence plots. This study introduces a previously unknown effect of wader foraging and bioturbation within this system, and highlights an area of wader science which could aid joint conservation and human provisioning action.

Many migratory birds are declining worldwide. In line with the general causes for the global biodiversity crisis, habitat loss, pollution, hunting, over-exploitation and climate change are thought to be at the basis of these population declines. Long-distance migrants seem especially vulnerable to rapid anthropogenic change, yet, the rate of decline across populations and species varies greatly within flyways. We hypothesize that differences in migration strategy, and notably stopover-site use, may be at the basis of these variations in resilience to global change. By identifying and comparing the migration strategies of two very closely related shorebird species, the Curlew sandpiper Calidris ferruginea and the Red-necked stint Calidris ruficollis, migrating from the same non-breeding site in Australia to similar breeding sites in the high Russian Arctic, we aimed to explain why these two species express differential resilience to rapid changes within their flyway resulting in different population trajectories in recent times. Based on 13 Curlew sandpiper and 16 Red-necked stint tracks from light-level geolocator tags, we found that individual Curlew sandpipers make use of fewer stopover areas along the flyway compared to Red-necked stints. Furthermore, and notably during northward migration, Curlew sandpipers have a higher dependency on fewer sites, both in terms of the percentage of individuals visiting key stopover sites and the relative time spent at those sites. While Curlew sandpipers rely mainly on the Yellow Sea region, which has recently experienced a sharp decline in suitable habitat, Red-necked stints make use of additional sites and spread their relative time en-route across sites more evenly. Our results indicate that differential migration strategies may explain why Curlew sandpipers within the East Asian-Australasian Flyway are declining rapidly (9.5%-5.5% per year) while Red-necked stints remain relatively stable (-3.1%-0%). We consider that more generally, the number of sites per individual and among a population, the spatial distribution across the flyway, as well as the relationship between the time spent over sites may prove to be key variables explaining populations and species' differential resilience to environmental change.

SummaryThe Spoon-billed Sandpiper Calidris pygmaea is a ‘Critically Endangered’ migratory shorebird. The species faces an array of threats in its non-breeding range, making conservation intervention essential. However, conservation efforts are reliant on identifying the species’ key stopover and wintering sites. Using Maximum Entropy models, we predicted Spoon-billed Sandpiper distribution across the non-breeding range, using data from recent field surveys and satellite tracking. Model outputs suggest only a limited number of stopover sites are suitable for migrating birds, with sites in the Yellow Sea and on the Jiangsu coast in China highlighted as particularly important. All the previously known core wintering sites were identified by the model including the Ganges-Brahmaputra Delta, Nan Thar Island and the Gulf of Mottama. In addition, the model highlighted sites subsequently found to be occupied, and pinpointed potential new sites meriting investigation, notably on Borneo and Sulawesi, and in parts of India and the Philippines. A comparison between the areas identified as most likely to be occupied and protected areas showed that very few locations are covered by conservation designations. Known sites must be managed for conservation as a priority, and potential new sites should be surveyed as soon as is feasible to assess occupancy status. Site protection should take place in concert with conservation interventions including habitat management, discouraging hunting, and fostering alternative livelihoods.

The Bay of Fundy, Canada is a critical migratory stopover for Semipalmated Sandpipers (Calidris pusilla) during fall migration. Recent ecological changes combined with range-wide population declines indicate that a re-evaluation of habitat use and regional fidelity is required. The Bay of Fundy is divided into three regions, each of which contains multiple foraging and roost sites. In this study, we examined local movement and regional fidelity within and between years using radio-telemetry and field-readable markers. We deployed 194 radio-transmitters and 2295 field-readable flags on Semipalmated Sandpipers during migration in 2013-2014, and resighted these birds, along with additional birds flagged in 2012, between 2013 and 2016. Radio-tracked birds used on average 1.3 to 4.1 foraging and roost sites per day, with most making multiple daily movements, but only 2% made permanent moves between geographically distant regions within the bay during stopover. Additionally, 97% of birds returned to their original region in subsequent years. The use of multiple sites suggests Semipalmated Sandpipers are capable of adapting to dynamic conditions in the Bay of Fundy on a local scale, but the high regional fidelity suggests that their ability to adapt to changes occurring at a regional scale may be limited. Uncertainty about the capability of Semipalmated Sandpipers to flexibly move among different regions of the Bay of Fundy supports the need for conservation at both the site and regional level.

Intertidal biofilm is a thin layer of microbes and meiofauna enmeshed in an extracellular polymeric matrix within and on top of mudflat sediment. This medium provides a dynamic resource for a variety of consumers in estuarine habitats, and is rich in essential fatty acids that birds require for long-distance migration. We measured seasonal changes in biofilm fatty acid content from spring to summer on the Fraser River Estuary, one of the richest and most important ecosystems for migrant and wintering waterbirds in Canada. Fatty acid content in biofilm showed a strong seasonal pattern with a peak in the spring that is associated with the northward migration of Western Sandpipers (Calidris mauri) to their breeding grounds. This peak is linked to the abundance and physiological state, and hence nutritional condition, of epipelic diatoms, which, in turn, depend on a combination of mudflat topography, salinity, temperature, and nutrients that can fluctuate widely with the freshwater inputs from the Fraser River. Specifically, areas with higher elevation (i.e., ∼1 m) had longer periods of exposure to ambient conditions (i.e., light, warm temperatures, gas exchange into/out of biofilms) that facilitated more biofilm growth and higher fatty acid content. Moreover, springtime changes in water chemistry (i.e., salinity/osmotic stresses and nutrients) and temperature facilitated the production of higher overall total lipid/fatty acid contents in the mudflat biofilms compared to summer. Effective conservation of migrating shorebirds depends on the protection of underlying processes at important stopover sites that promote biofilm communities to escalate their production of lipids, including essential fatty acids, during key times of the year.

Red knots (Calidris canutus) are shorebirds that spent most of the year at intertidal areas such as the Wadden Sea. However, once a year to and from their northern breeding grounds. Red knots yearly undergo a remodeling of their body to be physiologically prepared for the long flight and following reproductive season. Previous work has shown that many experienced migrants are very consistent in their migratory routines.The aim of this thesis is to increase understanding of the development of individual migratory routines. In the first part of this thesis, I first explore individual variation in migratory behaviour present in wild knots using a novel solar-powered satellite transmitter. In the second part of this thesis I investigate how differences in experience effect the development of physiological and behavioural traits in birds temporarily held in captivity. By combining these results I show that environmental conditions play a key role in shaping individual migratory routines. Expending on the role of experience in shaping individual differences I present a testing protocol aimed at testing cognitive aspects of migration, a fairly under represented topic in studies on migration. For future studies I suggest to combine tracking of individual birds with standardized assays to stimulate research into the cognitive aspects of migratory behaviour. Because I believe that the closer we are to understanding ‘what it is like to be a bird (or any other animal) the more we are able, and willing, to appreciate and protect the animals and the habitats that are around us.

Peregrine falcons (Falco peregrinus) have undergone a steady hemisphere-wide recovery since the ban on DDT in 1973, resulting in an ongoing increase in the level of danger posed for migrant birds, such as Arctic-breeding sandpipers. We anticipate that in response migrant semipalmated sandpipers (Calidris pusilla) have adjusted migratory behaviour, including a shift in stopover site usage towards locations offering greater safety from falcon predation.We assessed semipalmated sandpiper stopover usage within the Atlantic Canada Shorebird Survey dataset. Based on 3,030 surveys (totalling ∼32M birds) made during southward migration, 1974 - 2017, at 198 stopover locations, we assessed the spatial distribution of site usage in each year (with a ‘priority matching distribution’ index, PMD) in relation to the size (intertidal area) and safety (proportion of a site’s intertidal area further than 150m of the shoreline) of each location. The PMD index value is > 1 when usage is concentrated at dangerous locations, 1.0 when usage matches location size, and < 1 when usage is concentrated at safer locations.A large majority of migrants were found at the safest sites in all years, however our analysis of the PMD demonstrated that the fraction using safer sites increased over time. In 1974, 80% of birds were found at the safest 20% of the sites, while in 2017, this had increased to 97%. A sensitivity analysis shows that the shift was made specifically towards safer (and not just larger) sites. The shift as measured by a PMD index decline cannot be accounted for by possible biases inherent in the data set. We conclude that the data support the prediction that increasing predator danger has induced a shift by southbound migrant semipalmated sandpipers to safer sites.

Louse flies are blood-sucking ectoparasites of birds and mammals of veterinary and medical importance. These flies damage host skin and serve as vectors for blood-associated pathogens. Little is known about their phenology, host selection, and prevalence in wild birds. Our study provided a broad-scale assessment of louse flies parasitizing Charadrii and Scolopaci shorebirds during their migration through Central Europe. We collected louse flies from 3,129 specimens in 22 species of shorebirds at a major migratory stopover site in central Poland in 2011–17. In total, 31 Ornithomya avicularia and 15 Ornithomya chloropus specimens occurred on five wader species: Common Snipe (Gallinago gallinago), Ruff (Calidris pugnax), Dunlin (Calidris alpina), Curlew Sandpiper (Calidris ferruginea), and Wood Sandpiper (Tringa glareola). Prevalences ranged from 0.23% to 4.62%. No individual birds were infested by both species of fly, and no flies were found on an additional 17 wader species. The rarer of the two flies, O. chloropus, occurred on all infested bird species, whereas O. avicularia occurred only on Common Snipe and Curlew Sandpiper. In comparison with the other four infested wader species, Common Snipe (n=1,194) was more frequently infested with O. avicularia than with O. chloropus. Our study shows that the prevalence of louse flies on shorebirds is much lower than on other avian taxa. Ecologic and evolutionary mechanisms leading to the relative rarity of louse flies on shorebirds remain to be understood.

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...

Animal movements are inherently linked to landscape structure. Understanding this relationship for highly-mobile species requires documenting their responses to spatiotemporal variability of resources. To that end, characterizing movement behaviors and resource distributions using the principles of habitat connectivity facilitates coordinated landscape planning efforts within highly modified landscapes. We tracked locations and movements for 156 dunlin (Calidris alpina) and 109 long-billed dowitchers (Limnodromus scolopaceus) overwintering in two regions with distinct water distributions in California’s Central Valley. We then compared residency rates, functional connectivity to other regions, and associations between movement distances and average habitat availability and structural connectivity of habitat at multiple temporal and spatial scales. A widespread yet highly variable regional water distribution was associated with lower residency rates and substantially higher functional connectivity to nearby regions when compared to a stable regional water distribution characterized by a large, contiguous wetland complex. Longer movements were associated with decreasing average availability and spatial aggregation of surface water. Movement models suggested shorebirds primarily responded to habitat availability at smaller scales (

Naturally-occurring seasonal saltpans serve as a major foraging ground for migratory shorebirds. Nevertheless, little is known about the role of various environmental factors in determining the density, diversity and species richness of shorebirds and their prey in India. This study was designed to collect quantitative data for the first time on the role of season, salinity, water depth, and prey availability in influencing the density, diversity, and species richness of migratory shorebirds in the eastern coastal saltpans of Tamilnadu, India. Selected sites were classified as seasonal saltpans and hypersaline saltpans based on the concentration of salinity in water. Shorebirds were counted systematically from (August) 2012 to (May) 2015 using the total count method. The measurement of salinity level and water depths of each sighting was also collected. The density, diversity and species richness of shorebirds showed highest in the seasonal saltpans than the hypersaline saltpans. The monsoon season attracted more shorebird density, diversity species richness when compared to other seasons. Calidris alpine was only the migratory shorebird species recorded in both types of saltpans and across seasons. The micro and macro-invertebrate prey species showed the highest in the seasonal saltpans. The Chironomid larva showed the highest turnover than other species recorded in the studied saltpans. The multiple regression models showed that the year, season, salinity, and water depth influence the shorebird density, diversity, species richness, and prey species' density with a more significant percentage. The study results found that saltpans are also an ideal habitat for migratory shorebirds and their diverse prey species seasonally.

Gut microbes are increasingly recognised for their role in regulating an animal's metabolism and immunity. However, identifying repeatable associations between host physiological processes and their gut microbiota has proved challenging, in part because microbial communities often respond stochastically to host physiological stress (e.g. fasting, forced exercise or infection). Migratory birds provide a valuable system in which to test host-microbe interactions under physiological extremes because these hosts are adapted to predictable metabolic and immunological challenges as they undergo seasonal migrations, including temporary gut atrophy during long-distance flights. These physiological challenges may either temporarily disrupt gut microbial ecosystems, or, alternatively, promote predictable host-microbe associations during migration. To determine the relationship between migration and gut microbiota, we compared gut microbiota composition between migrating and non-migrating ("resident") conspecific shorebirds sharing a flock. We performed this across two sandpiper species, Calidris ferruginea and Calidris ruficollis, in north-western Australia, and an additional C. ruficollis population 3,000 km away in southern Australia. We found that migrants consistently had higher abundances of the bacterial genus Corynebacterium (average 28% abundance) compared to conspecific residents (average

We recorded 2 new bird species in Entre Ríos province, Argentina: Calidris canutus (Linnaeus, 1758) and Trogonsurrucura Vieillot, 1817. In addition, we present 25 noteworthy records for bird species in El Palmar National Park,Pre Delta National Park, and other parts of the province.

SummaryThe Critically Endangered Spoon-billed Sandpiper Calidris pygmaeus is one of the most threatened migratory shorebirds in the world, breeding in Russia and wintering in Asia. The global population is declining rapidly and is projected to be extinct within a few decades without intervention. Here, we present the results of shorebird surveys in previously unrecognised site in Bangladesh along the Meghna Estuary, identified for the first time by using species distribution models. Counts and habitat preference of Spoon-billed Sandpipers and other endangered shorebirds are described here with notes on the global importance of the newly discovered site. The sum of the peak counts for each shorebird species across the two surveys was 25,993 including a minimum of 48 Spoon-billed Sandpipers. The majority of the Spoon-billed Sandpipers were observed during low tide while foraging (66.6%) and logistic regression testing for effects on the presence of foraging Spoon-billed Sandpiper indicate that they mainly preferred to forage on shallow mud. We summarise the threats to Spoon-billed Sandpipers and other birds in the new site that is currently not recognized as a Wetland of International Importance under the Ramsar Convention, although it fulfils several Ramsar Criteria. We also propose conservation and monitoring measures for long-term protection of the Spoon-billed Sandpiper and its habitat.

Regular counts of migrating animals at stopover sites have been used as a measure of site importance at the global scale as well as for monitoring long-term population changes. However, migratory passage can last for several weeks and the turnover rate of individuals is often high, preventing the use of peak counts to estimate the total number of migrants. This estimate can be achieved, however, by combining count data with information on stopover length. Here, we developed a new method to quantify the total number of migrant birds using stopover areas hosting overlapping populations of local (breeding or wintering) and passage individuals of a given species. We illustrate the application of this method by estimating the number of spring migrant dunlins Calidris alpina stopping over at the Tagus estuary (Portugal). We used carbon and nitrogen isotopic signatures in toenails to identify migrants and to estimate their proportion in total counts. We then employed isotopic clock models to determine time since arrival (TSA) of individuals from signatures in red blood cells and plasma and, using a simulation approach, we derived the relationship between TSA and stopover length. Finally, by dividing the number of migrants.day (obtained from counts) by the stopover length, we assessed the size of the migrant population. We demonstrated that stopover length can be directly predicted from mean TSA values of birds sampled during migration, regardless of variations in (1) migratory rate, that is, the phenology of arrivals throughout the migratory period and (2) the number of birds involved in the migratory event. Migrant dunlins stayed on average 7.5 days at the Tagus estuary during spring migration, which combined with count data resulted in an estimate of c. 30,000 passage dunlins, using the study site. Our novel approach is not strict in its assumptions, and therefore can be customised to the specificities of different taxa and study areas. Estimates of total number of migrants along migratory flyways are critical to identify priority sites for conservation action. In fact, single stopover sites may host a very significant proportion of a global population albeit for a short period.

10 pages; International audience; Birds exhibit a wide diversity of breeding strategies. During incubation or chick-rearing, parental care can be either uniparental, by either the male or the female, or biparental. Understanding the selective pressures that drive these different strategies represents an exciting challenge for ecologists. In this context, assigning the type of parental care at the nest (e.g. biparental or uniparental incubation strategy) is often a prerequisite to answering questions in evolutionary ecology. The aim of this study was to produce a standardized method unequivocally to assign an incubation strategy to any Sanderling Calidris alba nest found in the field by monitoring nest temperature profiles. Using drops of >3 °C in nest temperature (recorded with thermistors) to distinguish incubation and recess periods, we showed that the number of recesses and the total duration of these recesses from 09:00 to 17:00 h UTC allowed us reliably (99.1% after 24 h and 100% when monitoring the nest for at least 4 days) to assign the incubation strategy at the nest for 21 breeding adults (14 nests). Monitoring nest temperature for at least 24 h is an effective method to assign an incubation strategy without having to re-visit nests, thereby saving time in the field and minimizing both disturbance and related increase in predation risk of clutches. Given the advantages of our method, we suggest that it should be used more widely in studies that aim to document incubation strategies and patterns in regions where ambient temperatures are at least 3 °C below the median nest temperature.

SummaryThe Yellow Sea region is of high global importance for waterbird populations, but recent systematic bird count data enabling identification of the most important sites are relatively sparse for some areas. Surveys of waterbirds at three sites on the coast of southern Jiangsu Province, China, in 2014 and 2015 produced peak counts of international importance for 24 species, including seven globally threatened and six Near Threatened species. The area is of particular global importance for the ‘Critically Endangered’ Spoon-billed Sandpiper Calidris pygmaea (peak count across all three study sites: 62 in spring [2015] and 225 in autumn [2014] and ‘Endangered’ Spotted Greenshank Tringa guttifer (peak count across all three study sites: 210 in spring [2014] and 1,110 in autumn [2015]). The southern Jiangsu coast is therefore currently the most important migratory stopover area in the world, in both spring and autumn, for both species. Several serious and acute threats to waterbirds were recorded at these study sites. Paramount is the threat of large-scale land claim which would completely destroy intertidal mudflats of critical importance to waterbirds. Degradation of intertidal mudflat habitats through the spread of invasive Spartina, and mortality of waterbirds by entrapment in nets or deliberate poisoning are also real and present serious threats here. Collisions with, and displacement by, wind turbines and other structures, and industrial chemical pollution may represent additional potential threats. We recommend the rapid establishment of effective protected areas for waterbirds in the study area, maintaining large areas of open intertidal mudflat, and the urgent removal of all serious threats currently faced by waterbirds here.

Using red knots ( Calidris canutus) as a model, we determined how changes in mass and metabolic activity of organs relate to temperature-induced variation in metabolic performance. In cold-acclimated birds, we expected large muscles and heart as well as improved oxidative capacity and lipid transport, and we predicted that this would explain variation in maximal thermogenic capacity (Msum). We also expected larger digestive and excretory organs in these same birds and predicted that this would explain most of the variation in basal metabolic rate (BMR). Knots kept at 5°C were 20% heavier and maintained 1.5 times more body fat than individuals kept in thermoneutral conditions (25°C). The birds in the cold also had a BMR up to 32% higher and a Msum16% higher than birds at 25°C. Organs were larger in the cold, with muscles and heart being 9–20% heavier and digestive and excretory organs being 21–36% larger than at thermoneutrality. Rather than the predicted digestive and excretory organs, the cold-induced increase in BMR correlated with changes in mass of the heart, pectoralis, and carcass. Msumvaried positively with the mass of the pectoralis, supracoracoideus, and heart, highlighting the importance of muscles and cardiac function in cold endurance. Cold-acclimated knots also expressed upregulated capacity for lipid transport across mitochondrial membranes [carnitine palmitoyl transferase (CPT)] in their pectoralis and leg muscles, higher lipid catabolism capacity in their pectoralis muscles [β-hydroxyacyl CoA-dehydrogenase (HOAD)], and elevated oxidative capacity in their liver and kidney (citrate synthase). These adjustments may have contributed to BMR through changes in metabolic intensity. Positive relationships among Msum, CPT, and HOAD in the heart also suggest indirect constraints on thermogenic capacity through limited cardiac capacity.

Semipalmated Sandpipers (Calidris pusilla (L., 1766)) that migrate through the upper Bay of Fundy, Canada, depend on a rich food supply to fuel their continued migration. Although past studies have reported a diet dominated by the amphipod Corophium volutator (Pallas, 1766), an animal rich in n–3 polyunsaturated fatty acids (PUFAs), recent evidence suggests that sandpiper diets are broad. This is beneficial in that it allows Semipalmated Sandpipers to respond to a changing food base, but quality of food is also important. PUFAs are important in providing the energy required by migrating birds and may play a role in migratory preparation. We assessed fatty acid (FA) concentrations and proportions in three common food items. We found that polychaetes should adequately meet the needs of migrating sandpipers in terms of FA composition. Concentrations of FAs in biofilm were low, but proportionally, n–3 PUFAs were well represented, particularly in biofilm collected in Shepody Bay, where it forms a substantial part of the sandpiper diet. Therefore, provided that birds can consume a sufficient volume of biofilm, it is also probably a suitable source of essential FAs. Our results suggest that Semipalmated Sandpipers in the Bay of Fundy can meet their FA needs with a variety of dietary options.

River deltas along Alaska’s Beaufort Sea coast are used by hatch-year semipalmated sandpipers (Calidris pusilla) after leaving their terrestrial natal sites, but the drivers of their use of these stopover sites on the first “hop” of fall migration are unknown. We quantified sandpiper temporal distribution and abundance as related to food resources at three river deltas during the beginning of their fall migration (post-breeding period) to compare the habitat quality among these deltas. We conducted population counts, sampled invertebrates, and captured birds to collect blood samples from individuals for triglyceride and stable isotope analyses to determine fattening rates and diet. Patterns of sandpiper and invertebrate abundance were complex and varied among deltas and within seasons. River deltas were used by sandpipers from late July to late August, and peak sandpiper counts ranged from 1000 to 4000 individuals, of which 98% were hatch-year semipalmated sandpipers. Isotopic signatures from blood plasma samples indicated that birds switched from a diet of upland tundra to delta invertebrate taxa as the migration season progressed, suggesting a dependence on delta invertebrates. Despite differences in diet among deltas, we found no differences in fattening rates of juvenile sandpipers as indicated by triglyceride levels. The number of sandpipers was positively associated with abundance of Amphipoda and Oligochaeta at the Jago and Okpilak-Hulahula deltas; an isotopic mixing model indicated that sandpipers consumed Amphipoda and Oligochaeta at Jago, mostly Chironomidae at Okpilak-Hulahula and Spionidae at Canning. Regardless of the difference in sandpiper diets at the Beaufort Sea deltas, their similar fattening rates throughout the season indicate that all of these stopover sites provide a critical food resource for hatch-year sandpipers beginning their first migration.

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...

To examine how habitat use by sandpipers (Calidris spp.; Baird's sandpipers, dunlin, least sandpipers, pectoral sandpipers, semipalmated sandpipers, stilt sandpipers, and white-rumped sandpipers) varies across a broad suite of environmental conditions, we conducted surveys at wetlands throughout the spring migratory period in 2013 and 2014 in 2 important stopover regions: the Rainwater Basin (RWB) in Nebraska, USA, and the Prairie Pothole Region (PPR) in South Dakota, USA. Because providing adequate energetic resources for migratory birds is a high priority for wetland management, we also measured invertebrate abundance at managed wetlands in the RWB to determine how food abundance influences the occupancy and abundance of sandpipers on wetlands throughout the migratory period. To quantify habitat use, we surveyed wetlands every 7–10 days in both regions and visually estimated wetland attributes. Our results indicate that invertebrate abundance predicted occupancy, but not abundance, of sandpipers at wetlands in the RWB. The wetland vegetation characteristics that predict sandpiper occupancy are similar in both regions, but wetlands in the PPR support a higher abundance of sandpipers than wetlands in the RWB. Our results suggest that sandpipers make stopover decisions that balance local and regional wetland conditions. Managers should maintain the cues (i.e., mudflat) and ecological conditions beyond invertebrate abundance that predict sandpiper habitat use to successfully provide resources for sandpipers during migratory stopover if that is a goal of wetland management. © 2017 The Wildlife Society.

We compiled a >50‐year record of morphometrics for semipalmated sandpipers (Calidris pusilla), a shorebird species with a Nearctic breeding distribution and intercontinental migration to South America. Our data included >57,000 individuals captured 1972–2015 at five breeding locations and three major stopover sites, plus 139 museum specimens collected in earlier decades. Wing length increased by ca. 1.5 mm (>1%) prior to 1980, followed by a decrease of 3.85 mm (nearly 4%) over the subsequent 35 years. This can account for previously reported changes in metrics at a migratory stopover site from 1985 to 2006. Wing length decreased at a rate of 1,098 darwins, or 0.176 haldanes, within the ranges of other field studies of phenotypic change. Bill length, in contrast, showed no consistent change over the full period of our study. Decreased body size as a universal response of animal populations to climate warming, and several other potential mechanisms, are unable to account for the increasing and decreasing wing length pattern observed. We propose that the post‐WWII near‐extirpation of falcon populations and their post‐1973 recovery driven by the widespread use and subsequent limitation on DDT in North America selected initially for greater flight efficiency and latterly for greater agility. This predation danger hypothesis accounts for many features of the morphometric data and deserves further investigation in this and other species.

1.Animals adjust to seasonal challenges in physical, behavioural and spatial ways. Such adjustments are commonly associated with diet changes that often can be characterised isotopically.2.We introduce the ‘double diet switch model’, with which the occurrence and timing of two subsequent diet switches of an individual animal can be traced with a single sample assayed for stable isotopes. We demonstrate the model for Sanderling, Calidris alba, a small shorebird that migrates from the Nearctic tundra breeding grounds to the intertidal flats of the Wadden Sea; during this migration some birds may stage in the North Atlantic areas.3.The ‘double diet switch model’ successfully predicted the occurrence and timing of two diet switches in 59 Sanderlings captured in the Wadden Sea in July–September. Excluding birds that likely had over-summered at North Atlantic staging areas, the model predicted that Sanderlings departed from the Arctic on 13 July (range: 9–17 July), had a staging duration of 18·6 days in the North Atlantic, and arrived in the Wadden Sea on 1 August (31 July–1 August).The estimated mean Arctic departure dates coincided with the mean hatching date, suggesting that many individuals failed to produce young or left the care to a partner. Estimated mean arrival date matched the main arrival period in the Wadden Sea obtained from observation data. In this study we did not use lipid-free tissues, which may bias model predictions. After correcting for lipid components, the estimated departure date was 11 days later and the staging duration 8·5 days shorter, while arrival date was similar.4.The ‘double diet switch model’ successfully identified the occurrence and timing of two subsequent diet switches. The ‘double diet switch model’ will not only apply to switches between three isotopic levels (as in the case study on Sanderling) but also to scenarios where the second switch reverses to the initial isotopic level. Due to this general applicability, the model can be adapted to a wide range of taxa and situations. Foreseeable applications include changes in habitat and food type, ontogenetic development or drastic phenotypic changes such as the metamorphosis in insects and amphibians

As the sun gradually lowers over the horizon, prey species with more sun in their eyes should have more difficulty in visually monitoring their surroundings for threats and thus experience a higher predation risk. In a unique setting, I could examine changes in antipredator behaviour in a prey species, the semipalmated sandpiper (Calidris pusilla), facing attacks by peregrine falcons (Falco peregrinus), which originated from the general direction of the lowering sun. I predicted gradual changes in antipredator behaviour as sun glare becomes more problematic later in the day. As the day progressed, sandpipers occurred in sparser groups when the sun glared but not when clouds obscured the sun, suggesting that fewer individuals engaged in risky foraging. Pecking rate and foraging success decreased later in the day when the sun glared but not otherwise implying an increase in vigilance at the expense of foraging. When more sun hit their eyes, sandpipers also moved faster suggesting increased skittishness. The sun glare effect might be relevant to any species foraging in open areas not only when the sun sets but also when it rises especially if predators can target prey species at these vulnerable times. The temporal gradient in predation risk that the sun glare effect creates might thus apply broadly and have important consequences for antipredator vigilance, foraging efficiency, and habitat use. This article is protected by copyright. All rights reserved.

Males of many polygynous species compete for access to fertile females without providing them with resources other than sperm and without investing in care for the offspring (male dominance polygyny). In such systems, local competition for access to females is intense and typically only a few males obtain matings, leading to strong sexual selection. Sampling multiple breeding areas could then provide a mechanism for males to increase their chances to reproduce. However, little is known about such sampling behaviour and about the spatial scale at which males compete. Here we show that most males of a migratory, polygynous shorebird, the pectoral sandpiper (Calidris melanotos), that arrived at a known breeding location in northern Alaska subsequently moved through a considerable part of the entire species' breeding range (up to 13,045 km in a four-week period), sampling as many as 23 additional potential breeding sites. Our data suggest that males do not have a final breeding destination after migration from their wintering quarters, but make nomadic movements that are probably not a consequence of breeding failure. Tenure, the duration of stay at a site, correlated strongly with the number of breeding females at the site, suggesting that decisions to leave are dependent on local mating opportunities. Nomadic movements may allow males to display and sire offspring at multiple sites within a single breeding season. Sexual selection may then favour high-performance males that are able to reduce sleep to compete locally and to fly long distances between breeding sites, leading to a population with unrestricted interbreeding and without local adaptation and speciation.

The relevance of the study of hydrophilic birds in the urban areas of the Black Sea coast is due to their important role in the coastal biocoenosis structure and the need to preserve biodiversity in the conditions of anthropogenic transformation of Crimean coastal zone. The dynamics of species composition and abundance of birds in Kruglaya (Omega) Bay (Sevastopol) were investigated. The results of regular and episodic monitoring carried out in 1995 and 2005–2016 were used in this work. Quantitative accounting was carried out only in January and February (1–2 times per winter season) in 2005–2008, episodically in 2009–2013 and weekly in December — May 2014/2015 and September — May 2015/2016. Number of specimens per species was registered, and the ratio of young and adult specimens in mute swan (Cygnus olor), sex ratio in mallard (Anas platyrhynchos), common pochard (Aythya ferina) and tufted duck (Aythya fuligula) were determined. Russian and Latin names of birds are represented by L. S. Stepanian. Kruglaya Bay is one of Sevastopol bays which form the northern coastline of the Heraclea Peninsula, and it is a place of seasonal concentrations of hydrophilic birds. The basic morphometric characteristics of the bay are the following: the water area — 0.64 km2, length — 1.3 km, maximum width — 0.8 km, the average depth — 4.5 m. The water area of the bay did not freeze usually, only its inner part was covered with ice in extremely cold winters. Benthic macrophyte species are represented by two associations: Cystoseira crinita and C. barbata on stones and rocks, and Zostera noltii and Z. marina on sandy and silty areas. Two local areas of common reed (Phragmites australis) beds are located in the inner part of the bay. The zoobenthos is a significant part of the food supply of birds and includes 97 species, mainly polychaetes, molluscs and crustaceans. The ichthyofauna is represented by 42 fish species. 51 species of aquatic and semi-aquatic birds across 8 Orders were identified. The winter bird community was most diverse and numerous (32 species: 14 Anseriformes, 7 Charadriiformes, 5 Podicipediformes, 3 Gruiformes, 2 Pelecaniformes, 1 Gaviiformes). Eight species dominate regularly in winters and quantitatively — mute swan, mallard, common pochard, tufted duck, eurasian coot (Fulica atra), black-headed gull (Larus ridibundus), caspian gull (Larus cachinnans) and common gull (Larus canus). Rare species wintering in the Mountain Crimea, including horned grebe (Podiceps auritus), Bewick’s swan (Cygnus bewickii), red-breasted goose (Rufibrenta ruficollis), white-headed duck (Oxyura leucocephala), knot (Calidris canutus), is of great interest. The average ratio of young and adult mute swans in the main wintering period (December — February) was 61 : 39 % in 2014/2015 and 45 : 55 % in 2015/2016, respectively. The ratio of males and females were as follows: in mallard 49.5 : 50.5 % in 2014/2015, and 51.4 : 48.6 % in 2015/2016; in common pochard 54.8 : 45.2 % in 2014/2015, and 60.5 : 39.5 % in 2015/2016; in tufted duck 51.0 : 49.0 % in 2014/2015, and 51.4 : 48.6 % in 2015/2016, respectively. Formation of the winter bird community began in October, sometimes at the end of September when single specimens of mallard, coot, tufted duck, red-breasted merganser (Mergus serrator), black-necked grebe (Podiceps nigricollis) appeared. Common gull, great crested grebe (Podiceps cristatus) and the common pochard come flying in November; the mute swan appears at the beginning of December. Maximum and relatively stable number of most species was typical for January and the first half of February. Maximum number of specimens of all bird species was registered in January 13, 2015 (1288), and February 7, 2016 (1531 specimens). The feeding conditions of Kruglaya Bay allow overwintering of the birds with different feeding specializations. The benthophages (most of Anseriformes and Coot) rank first in species richness (at least 13 species) and in quantitative terms. Five species (black-throated diver (Gavia arctica), great cormorant (Phalacrocorax carbo), common sheg (Phalacrocorax aristotelis), red-breasted merganser, Sandwich tern (Thalasseus sandvicensis)) form the group of ichthyophages. The Grebes occupy an intermediate position between benthophages and ichthyophages: small fish and benthic invertebrates are present in their diet. Four species of gull (black-headed, Caspian, common, Mediterranean gull (Larus melanocephalus)) constitute a group of omnivores. The rare visitors in Kruglaya Bay are zoophagous and omnivorous birds foraging in the surf zone and at shallow depths, such as water rail (Rallus aquaticus), common moorhen (Gallinula chloropus), dunlin (Calidris alpina), knot (Calidris canutus), and herbivores which prefer to feed in terrestrial habitats — red-breasted goose (Rufibrenta ruficollis). The nutritional requirements of birds are compensated to a certain extent by additional feeding carried out by townspeople. In general 30 passing and nomadic species, mainly Charadriiformes (11), Anseriformes (7) and Ciconiiformes (5), were registered. A nesting bird community was absent, and only the nesting of little bittern (Ixobrychus minutus) was registered in 2016 for the first time in city zone. The spring migration took place from late February to May, the autumn migration — from August until the first decade of November. Kruglaya Bay is a valuable natural and ecological educational place and deserves status as a natural park.

Analysis of the biometric parameters of dunlins is based on data of 496 adult birds and 214 birds in their second year of life captured during the spring migration in the years 2002–2014 in the floodplain of the Pripyat River in southern Belarus. The average size of the dunlins caught in this area shows that the majority of birds correspond to the parameters of the nominate subspecies (C. a. alpina). We have not found any statistically significant differences between the age groups in all morphometric parameters except for the length of the wing, which in the birds in their second year of life is slightly smaller than in adults. Both the adult dunlins and the yearlings have two peaks in the distribution of biometric parameters, such as the bill length to the nostril, the bill length to the feathering, the total length of the head with the bill, and the length of the wing, which is associated with differences in the size of males and females. We have noted an increase in the average bill length to the nostril, bill to feathering length, and the total length of the head with the bill, as well as the wing length in the adult birds captured during the spring migration. These values are especially significant in the last five days of May. The body mass index of the dunlins passing through the floodplain of the Pripyat River increases intensively during the migration, which can partly be attributed to the later migration of large birds (females). However, the main reason for the increase in the body mass index is that the birds migrating later in spring have higher energy reserves compared with the earlier migrants. At the end of the migration period, in the floodplain of the Pripyat River, the body mass indices of dunlins are very high. This suggests that birds leaving the stopover site in southern Belarus in early June have sufficient energy resources to reach the nesting places in one nonstop flight.