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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.

Each year, thousands of Nearctic shorebirds migrate from breeding grounds in the northern hemisphere to wintering grounds in South America. At the wintering sites, in addition to moulting their flight feathers and plumage, shorebirds engage in feeding to increase body mass to gain sufficient energy for the return migration to the breeding grounds. This study aims to describe the temporal variation of body mass and plumage of the Semipalmated Plover (Charadrius semipalmatus), Spotted Sandpiper (Actitis macularius), Sanderling (Calidris alba) and Semipalmated Sandpiper (Calidris pusilla) during the wintering season on the north-eastern coast of Brazil and to evaluate the relationship between mass gain and plumage moulting. The lowest average masses for each of these species were recorded in October, November, December and January, usually when displaying non-breeding plumage. Shorebirds with intermediate and breeding plumage were frequently recorded in the migration preparation period beginning in April, with a significant increase in body mass. However, for some individuals low masses were recorded late during the wintering period and these were all found to be actively moulting. The highest values for body mass were recorded for shorebirds with breeding and intermediate plumage that were not actively moulting, nearing the end of wintering period.

Contemporary declines of shorebirds have been linked to environmental causes, but the role of predation in shorebird declines is not clear. From 1994 to 2015, we observed the interactions of Peregrine Falcons (Falco peregrinus) and Dunlin (Calidris alpina) wintering on the Pacific coast of British Columbia. Peregrine sightings per hour of observation declined on a seasonal basis from October to February, but increased chronologically from 0.36/hr in 1994 to 1.24/hr in 2015. Peregrines captured 205 Dunlin in 1369 attacks. Hunting success rates increased from 10.8% in October to 15.0% in the winter months. During high tide, when the intertidal zone was flooded, some Dunlin flocks spent up to 315 min in sustained flight over the ocean, apparently as an antipredator strategy, but other flocks roosted on the foreshore, or sat out the high-tide interval on agricultural fields inland. This study suggests that these anti-predator behaviors allow the Dunlin population to persist at Boundary Bay as predato...

The spoon-billed sandpiper Calidris pygmaea is a Critically Endangered shorebird that breeds in the Russian arctic and winters in coastal and estuarine habitats in South-east Asia. We report the first formal estimate of its global population size, combining a mark–resighting estimate of the number of leg-flagged individuals alive in autumn 2014 with an estimate of the proportion of birds with flags from scan surveys conducted during the same period at a migration stop-over site on the Jiangsu coast of China. We estimate that the world breeding population of spoon-billed sandpipers in 2014 was 210–228 pairs and the post-breeding population of all age classes combined was 661–718 individuals. This and related methods have considerable potential for surveillance of the population size of other globally threatened species, especially widely dispersed long-distance migrants.

A single individual of feather mite Alloptes (Conuralloptes) calidridis Dubinin, 1951 is reported from the covert feathers of a juvenile Dunlin Calidris alpina Linnaeus, 1758. A redescription of a ...

Little is known about environmental influences on radial glia-like (RGL) α cells (radial astrocytes) and their relation to neurogenesis. Because radial glia is involved in adult neurogenesis and astrogenesis, we investigated this association in two migratory shorebird species that complete their autumnal migration using contrasting strategies. Before their flights to South America, the birds stop over at the Bay of Fundy in Canada. From there, the semipalmated sandpiper (Calidris pusilla) crosses the Atlantic Ocean in a non-stop 5-day flight, whereas the semipalmated plover (Charadrius semipalmatus) flies primarily overland with stopovers for rest and feeding. From the hierarchical cluster analysis of multimodal morphometric features, followed by the discriminant analysis, the radial astrocytes were classified into two main morphotypes, Type I and Type II. After migration, we detected differential changes in the morphology of these cells that were more intense in Type I than in Type II in both species. We also compared the number of doublecortin (DCX)-immunolabeled neurons with morphometric features of radial glial–like α cells in the hippocampal V region between C. pusilla and C. semipalmatus before and after autumn migration. Compared to migrating birds, the convex hull surface area of radial astrocytes increased significantly in wintering individuals in both C. semipalmatus and C. pusilla. Although to a different extent we found a strong correlation between the increase in the convex hull surface area and the increase in the total number of DCX immunostained neurons in both species. Despite phylogenetic differences, it is of interest to note that the increased morphological complexity of radial astrocytes in C. semipalmatus coincides with the fact that during the migratory process over the continent, the visuospatial environment changes more intensely than that associated with migration over Atlantic. The migratory flight of the semipalmated plover, with stopovers for feeding and rest, vs. the non-stop flight of the semipalmated sandpiper may differentially affect radial astrocyte morphology and neurogenesis.

The Gulf of Maine has long been recognized as a major stopover area for shorebirds in fall. Knowing how birds move within and beyond the region will be paramount to protecting threatened shorebird habitat. To determine stopover behavior during fall migration (2013–2017) in Maine, 180 (104 AHY, 76 HY) Semipalmated Sandpipers, Calidris pusilla, were tracked using VHF radiotelemetry and an extensive array of automated receivers (Motus Wildlife Tracking System). Birds tagged at three locations along the Maine coastline showed no effect of age class or stopover site on body condition (body mass, estimated fat mass) or stopover length (post-capture detection period). However, movement after departure varied greatly among sites. Few birds captured at the northern-most site (“Downeast,” n = 71), which had the greatest amount of mudflats and offshore roost sites and the least amount of human disturbance, were detected beyond the initial tagging location, suggesting that they, like birds in the Bay of Fundy just to the north, initiated trans-oceanic flights from that location. At the Downeast site, leaner birds remained significantly longer than fatter birds, suggesting that time of departure there depended on energy reserves, which would be critical for making extensive flights. In contrast, over half of the birds tagged further south (Popham Beach, n = 59; Rachel Carson NWR, n = 50) were later detected at coastal locations to the north (few) or to the south (most). Stopover period at these sites was independent of fat, suggesting that other factors (e.g., feeding/roosting site availability, human activity) influenced departure decisions. In Maine, Semipalmated Sandpipers, regardless of age, may move north (Downeast) or south (e.g., Cape Cod, Rhode Island, Long Island Sound) where the local topography, habitat characteristics (feeding/roosting sites), and/or lower human activity, may best enable them to initiate trans-oceanic flights to the wintering grounds. Future study should determine if variation in stopover behavior is population-specific and if population-segregation occurs in Maine. Use of automated VHF radiotelemetry has led to a greater understanding of stopover behavior and the degree of connectivity among stopover sites, which should be taken into account for conserving migratory bird habitat across broad spatial scales.

Pouco se sabe sobre as influências ambientais nas células radiais α semelhantes à glia (astrócitos radiais) e sua relação com a neurogênese. Como a glia radial participa da neurogênese e da astrogênese em adultos, iremos investigar essa questão em duas aves marinhas migratórias que completam sua migração outonal usando rotas migratórias contrastantes. Antes de seus voos para a América do Sul, as aves fazem escala na Baía de Fundy, no Canadá, e a partir daí o maçarico semipalmado (Calidris pusilla) atravessa o Oceano Atlântico em um voo sem escalas de 5 dias, enquanto a tarambola semipalmada (Charadrius semipalmatus) voa principalmente sobre o continente, com escalas para descanso e alimentação. Usando análise hierárquica de cluster e discriminante de características morfométricas para classificar células reconstruídas tridimensionalmente, encontramos dois morfotipos diferentes de glia radial designados Tipo I e Tipo II. Estas células foram afetadas diferencialmente pelo processo migratório com alterações morfológicas mais intensas no morfotipo Tipo I do que no Tipo II em ambas as espécies. Nós também comparamos o número de neurônios marcados com duplacortina (DCX) com características morfométricas de células semelhantes às glias radiais α na região V do hipocampo do C. pusilla e C. semipalmatus antes e depois da migração no outono. Descobrimos que, em comparação com as aves migratórias, a superfície do convex hull dos astrócitos radiais nas aves invernais aumentou significativamente em C. semipalmatus e C. pusilla e isso parece correlacionado com um aumento do número total de neurônios jovens imunomarcados para DCX em aves invernantes. Apesar das diferenças filogenéticas a diminuição da complexidade morfológica dos astrócitos radiais no maçarico semipalmado e seu aumento na tarambola semipalmada, uma espécie que provavelmente depende mais da informação visuoespacial para a navegação, pode ter implicações funcionais importantes. O voo migratório da tarambola semipalmada, com paradas para alimentação e repouso, versus o voo sem parada do maçarico semipalmado, parece afetar diferencialmente a morfologia e a neurogênese dos astrócitos radiais. Little is known about environmental influences on radial glia–like α cells (radial astrocytes) and their relation to neurogenesis. Because radial glia is involved in adult neurogenesis and astrogenesis, we investigated this association in two migratory shorebird species that complete their autumnal migration using contrasting strategies. Before their flights to South America, the birds stop over at the Bay of Fundy in Canada. From there, the semipalmated sandpiper (Calidris pusilla) crosses the Atlantic Ocean in a non-stop 5-day flight, whereas the semipalmated plover (Charadrius semipalmatus) flies primarily overland with stopovers for rest and feeding. Using hierarchical cluster and discriminant analysis of morphometric features to classify three-dimensionally (3D) reconstructed cells, we identified two morphotypes of radial glia, designated as Type I and Type II. The migratory process affected these cells differentially, with more intense morphological changes in Type I than in Type II morphotypes in both species. We also compared the number of doublecortin (DCX)-immunolabeled neurons with morphometric features of radial glial–like α cells in the hippocampal V region between C. pusilla and C. semipalmatus before and after autumn migration. Compared with migrating birds, the convex hull surface of radial glial–like α cells of wintering birds significantly increased in both C. semipalmatus and C. pusilla. This increase correlated with an increase of the total number of DCX-immunolabeled neurons in wintering birds. The decreased radial astrocyte morphological complexity in the semipalmated sandpiper and its increase in the semipalmated plover, a species that probably relies more on visuospatial information for navigation, may be significant, despite phylogenetic and other differences between these taxa. The migratory flight of the semipalmated plover, with stopovers for feeding and rest, versus the non-stop flight of the semipalmated sandpiper may differentially affect radial astrocyte morphology and neurogenesis.

Technological constraints have limited our ability to compare and determine the proximate and ultimate drivers of migratory behavior in small-bodied birds. Small VHF transmitters (9,000 km; pectoral sandpiper, Calidris melanotos, and white-rumped sandpiper, Calidris fuscicollis) would be more likely to migrate with characteristics of a time-minimizing migration strategy compared to species migrating intermediate distances (5,000–7,500 km; semipalmated sandpiper, Calidris pusilla; and lesser yellowlegs, Tringa flavipes) or shorter distances (~5,000 km; least sandpiper, Calidris minutilla; semipalmated plover, Charadrius semipalmatus), which would migrate with more characteristics of an energy-minimizing strategy. Our results indicate that migration and stopover behaviors for adults matched this prediction; longer distance migrants had longer stopover lengths, departed with higher relative fuel loads, flew with faster ground and airspeeds, and had a lower probability of stopover in North America after departing the subarctic. The predicted relationship between migration distance and migratory strategy was not as clear for juveniles. Despite our prediction that longer distance migrants would be less wind selective at departure and fly into headwinds en route, all species and age classes departed and migrated with supportive winds. Birds with higher estimated fuel loads at departure were less likely to stop in North America after departing the subarctic, indicating that some birds attempted non-stop flights from the subarctic to the Caribbean or South America. Additionally, within species, adults with higher relative fuel loads at departure had a higher detection probability after departing the subarctic, which we interpret as evidence of higher survival compared to juveniles. This study shows that migratory behavior of shorebirds has predictable patterns based on migration distance that are moderated by body condition of individuals, with potential implications for fitness.

To successfully perform their long-distance migrations, migratory birds require sites along their migratory routes to rest and refuel. Monitoring the use of so-called stopover and staging sites provides insights into (a) the timing of migration and (b) the importance of a site for migratory bird populations. A recently developed Bayesian superpopulation model that integrates mark-recapture data and ring density data enabled the estimation of stopover timing, duration, and population size. Yet, this model did not account for heterogeneity in encounter (p) and staying (phi) probabilities. Here we extended the integrated superpopulation model by implementing finite mixtures to account for heterogeneity in p and phi. We used simulations and real data (from 2009-2016) on red knots Calidris canutus, mostly of the subspecies piersmai, staging in Bohai Bay, China, during spring migration to (a) show the importance of accounting for heterogeneity in encounter and staying probabilities to get unbiased estimates of stopover timing, duration, and numbers of migratory birds at staging sites and (b) get accurate stopover parameter estimates for a migratory bird species at a key staging site that is threatened by habitat destruction. Our simulations confirmed that heterogeneity in p affected stopover parameter estimates more than heterogeneity in phi, especially when most birds had low p. Bias was particularly severe when most birds had both low phi and p. Bias was largest for population size, intermediate for stopover duration and negligible for stopover timing. A total of 50,000-100,000 red knots were estimated to annually stop for 5-9 days in Bohai Bay between 10 and 30 May. This shows the key importance of this staging site for this declining species. There were no clear changes in stopover parameters over time, although stopover population size was substantially lower in 2016 than in preceding years. Our study shows the importance of accounting for heterogeneity in both encounter and staying probabilities for accurately estimating stopover duration and population size and provides an appropriate modeling framework.

Biparental care for offspring requires cooperation, but it is also a potential source of conflict, since one parent may care less at the expense of the other. How, then, do parents respond to the reduction of their partner’s care? Theoretical models predict that parents that feed offspring should partially compensate for the reduced care of their partner. However, for incubating birds partial compensation is unlikely the optimal strategy, because the entire brood can fail with reduced care. Although biparental incubation dominates in non-passerine birds, short-term manipulations of parental care and evaluations of individual differences in the response, both crucial to our understanding of parental cooperation, are scarce. Here, we describe the response of semipalmated sandpiper (Calidris pusilla) parents to a 24-hour removal of their partner during the incubation period, explore factors that can explain individual variation in the response, and describe how incubation rhythms changed after the removed parent returned. On average, the parents compensated partially for the absence of their partner’s care (59%; 95%CI: 49-70%,N= 25 individuals). The level of compensation did not differ between the sexes. However, individual responses varied from no to full compensation (2-101%). In seven nests where the removed parent never returned, the widowed parent attended the nest for 0-10 days (median: 4 days). In contrast to patterns observed in undisturbed nests or in uniparental species, nest attendance during compensation tended to be higher during the warmer part of the day. Although the level of compensation was not related to the before-experimental share of incubation, more responsive parents (that left the nest earlier upon human approach) compensated more. The quality of incubation in the after-experimental period was lower than usual, but improved quickly over time. Our findings suggest that full compensation might be limited by energetic constraints or by variation in responsiveness to the absence of the partner. Nevertheless, semipalmated sandpiper parents are able to adjust their subsequent incubation behaviour to take full responsibility for the nest when widowed. Because (nearly) full compensation was the most common response, we speculate that all individuals attempt full compensation, but that some fail because their energy stores get depleted, or because they are less responsive to the absence of their partner.

A recent study demonstrated that semipalmated sandpiper (Calidris pusilla) wing lengths have shortened from the 1980s to the present-day. We examined alternative and untested hypotheses for this change at an important stopover site, James Bay, Ontario, Canada. We evaluated morphometric patterns in wing length and bill length by age and sex, when possible, and assessed if wing shape has also changed during this time-period. We investigated patterns of morphological change in two additional Calidridine sandpipers, white-rumped sandpipers (Calidris fuscicollis) and least sandpipers (Calidris minutilla), to determine if shorter wing lengths are a widespread pattern in small sandpipers. We also examined allometric changes in wing and bill lengths to clarify if wing length declines were consistent with historical scaling relationships and indicative of a change in body size instead of only wing length change. We found that including sex and wing shape in analyses revealed important patterns in morphometric change for semipalmated sandpipers. Wing lengths declined for both sexes, but the magnitude of decline was smaller and not significant for males. Additionally, semipalmated sandpiper wings have become more convex, a shape that increases maneuverability in flight. Wing lengths, but not bill lengths, declined for most species and age classes, a pattern that was inconsistent with historical allometric scaling relationships. For juvenile semipalmated sandpipers, however, both bill and wing lengths declined according to historical scaling relationships, which could be a consequence of nutritional stress during development or a shift in the proportion of birds from smaller-sized, western breeding populations. Except for juvenile semipalmated sandpipers, we did not find evidence for an increase in the proportion of birds from different breeding populations at the stopover site. Given the wide, hemispheric distribution of these sandpipers throughout their annual cycles, our results, paired with those from a previous study, provide evidence for wide-spread reduction in wing lengths of Calidridine sandpipers since the 1980s. The shorter wing lengths and more convex wing shapes found in this study support the hypothesis that selection has favored more maneuverable wing morphology in small sandpipers.

Migratory birds undergo impressive body remodelling over the course of an annual cycle. Prior to long-distance flights, red knots (Calidris canutus islandica) reduce gizzard mass while increasing body mass and pectoral muscle mass. Although body mass and pectoral muscle mass are functionally linked via their joint effects on flight performance, gizzard and pectoral muscle mass are thought to be independently regulated. Current hypotheses for observed negative within-individual covariation between gizzard and pectoral muscle mass in free-living knots are based on a common factor (e.g. migration) simultaneously affecting both traits, and/or protein limitation forcing allocation decisions. We used diet manipulations to generate within-individual variation in gizzard mass and test for independence between gizzard and pectoral muscle mass within individuals outside the period of migration and under conditions of high protein availability. Contrary to our prediction, we observed a negative within-individual covariation between gizzard and pectoral muscle mass. We discuss this result as a potential outcome of an evolved mechanism underlying body remodelling associated with migration. Although our proposed mechanism requires empirical testing, this study echoes earlier calls for greater integration of studies of function and mechanism, and in particular, the need for more explicit consideration of the evolution of mechanisms underlying phenotypic design.

Background Space use strategies by foraging animals are often considered to be species-specific. However, similarity between conspecific strategies may also result from similar resource environments. Here, we revisit classic predictions of the relationships between the resource distribution and foragers’ space use by tracking free-living foragers of a single species in two contrasting resource landscapes. At two main non-breeding areas along the East-Atlantic flyway (Wadden Sea, The Netherlands and Banc d’Arguin, Mauritania), we mapped prey distributions and derived resource landscapes in terms of the predicted intake rate of red knots (Calidris canutus), migratory molluscivore shorebirds. We tracked the foraging paths of 13 and 38 individual red knots at intervals of 1 s over two and five weeks in the Wadden Sea and at Banc d’Arguin, respectively. Mediated by competition for resources, we expected aggregation to be strong and site fidelity weak in an environment with large resource patches. The opposite was expected for small resource patches, but only if local resource abundances were high. Results Compared with Banc d’Arguin, resource patches in the Wadden Sea were larger and the maximum local resource abundance was higher. However, because of constraints set by digestive capacity, the average potential intake rates by red knots were similar at the two study sites. Space-use patterns differed as predicted from these differences in resource landscapes. Whereas foraging red knots in the Wadden Sea roamed the mudflats in high aggregation without site fidelity (i.e. grouping nomads), at Banc d’Arguin they showed less aggregation but were strongly site-faithful (i.e. solitary residents). Conclusion The space use pattern of red knots in the two study areas showed diametrically opposite patterns. These differences could be explained from the distribution of resources in the two areas. Our findings imply that intraspecific similarities in space use patterns represent responses to similar resource environments rather than species-specificity. To predict how environmental change affects space use, we need to understand the degree to which space-use strategies result from developmental plasticity and behavioural flexibility. This requires not only tracking foragers throughout their development, but also tracking their environment in sufficient spatial and temporal detail. Electronic supplementary material The online version of this article (10.1186/s40462-018-0142-4) contains supplementary material, which is available to authorized users.

Shorebirds depend on staging sites in the Gulf of Mexico that are frequently subject to pollution by oil and its toxic constituents, polycyclic aromatic hydrocarbons (PAHs). It was hypothesized that PAH contamination lowers staging site quality for migratory shorebirds, with consequences for fueling and departure timing. Sediment total PAH concentrations were measured at six staging sites along the Texas and Louisiana Gulf Coast. Sites in Louisiana were expected to have higher total PAH concentrations as they were more heavily impacted by the Deepwater Horizon oil spill. From 2015 to 2017, 165 Sanderling ( Calidris alba) and 55 Red knots ( C. canutus) were captured at these same sites during their northward migration (late April to mid May). Mass, body morphometrics, and plasma metabolite measurements were taken to determine fuel loads and fueling rates, and a subset of birds (120 Sanderling and 39 Red knots) received a coded radio tag to determine departure dates using the Motus telemetry array. Compared to Texas sites, sediment in Louisiana had higher total PAH concentrations, dominated by heavier 6 ring indeno[1,2,3- cd]pyrene (48%). Plasma metabolite profiles suggested that fueling rates for Sanderling, but not Red knots, tended to be lower in Louisiana, and both species departed later than the study average from Louisiana. However, multiple factors, including migration patterns, food supply, and other contaminants, also likely influenced fueling and departures. PAH contamination in the Gulf of Mexico remains an ongoing issue that may be impacting the staging site quality and migration timing of long-distance migratory birds.

Spatiotemporal dynamics may present different levels of regional or local stability, generally attributed to local habitat and landscape factors, reflecting the tolerances and ecological requirements of the populations. In this study, we examined the variations of dunlin abundance and occurrence in twenty-three wetlands of the “La Mancha Húmeda” Biosphere Reserve, central Spain, between October 2010 and July 2017. In addition, we observed the variations of local abundance in the lakes of the Manjavacas lagoon complex, seeking to understand the factors that determine the local movements of the wintering individuals. Eleven lakes had records of dunlin, but most of individuals (ca. 90%) were observed in the Manjavacas Lagoon Complex (Alcahozo and Manjavacas lakes). The preference for this complex associated with temporal variations of abundance between the Alcahozo and Manjavacas lagoons possibly reflects the specific characteristics of the invertebrate community available as prey, especially for the presence of anostracans and copepods. The results of this study are a first step in understanding the factors that lead this species to select continental wetlands as wintering sites.

Predator recovery driven by single-species management approaches may lead to conservation conflicts between recovered predators and prey species of conservation concern. As part of an aggressive recovery plan, the Eastern Peregrine Falcon Recovery Team released (1975–1985) 307 captive-reared peregrine falcons (Falco peregrinus) and successfully established a breeding population within the mid-Atlantic Coastal Plain, a physiographic region with no historic breeding population and a critical spring staging area for migratory shorebirds. We examined the influence of resident falcons on the distribution of foraging red knots during spring migration. We conducted weekly aerial surveys (2006–2009) along the Virginia barrier islands during the spring staging period (25 April– 6 June) to map foraging red knots (Calidris canutus) and evaluated the influence of proximity (0–3, 3–6, >6 km) of beaches to active peregrine falcon nests on knot density (birds/km). Accumulated use of beaches throughout the season by red knots was significantly influenced by proximity of beaches to active falcon nests such that mean density was more than 6 fold higher on beaches that were >6 km compared to beaches that were only 0–3 km from active eyries. Whether or not an eyrie was used in a given year had a significant influence on the use of associated close (0–3 km) beaches. From 6.5 to 64 fold more knots used beaches when associated eyries were not active compared to when they were active depending on the specific site. Historically, red knots and other migratory shorebirds would have enjoyed a peregrine-free zone within this critical staging site. The establishment of a dense breeding population of falcons within the area represents a new hazard for the knot population.

Wetland connectivity provides migratory shorebirds varying options to meet energy requirements to survive and complete their annual cycle. Multiple factors mediate movement and residency of spatially segregated wetlands. Information on these factors is lacking in the tropics, yet such information is invaluable for conservation design. The influence of seven biotic and abiotic factors on local movement and residency rates of Semipalmated Sandpipers (Calidris pusilla) among three major wetlands in southwestern Puerto Rico in 2013–2014 was assessed using multi-state models. The model with highest support (AICc wi= 0.78) indicated that weekly residency rates increased seasonally, and were positively influenced by bird abundance and the interaction of prey density and rainfall. Movement rates were negatively influenced by inter-wetland distance, which varied annually, ranging from 0.01 ± 0.004 to 0.33 ± 0.08. Age class (adult, juvenile), extent of shoreline habitat (km), and body condition (estimated...

Semipalmated Sandpipers (Calidris pusilla) and Lapland Longspurs (Calcarius lapponicus) share similar nesting habitat preferences on small islands in the Mackenzie River Delta, Northwest Territories, Canada. A Semipalmated Sandpiper was observed incubating a mixed clutch of its own eggs with two smaller eggs presumed to be from a Lapland Longspur. This is a unique combination of a precocial and an altricial species' eggs in the same nest. Possible explanations for the occurrence of this interspecific mixed clutch include nest parasitism, accidental laying, opportunistic egg dumping, or nest usurpation.

Niche differentiation through resource partitioning is seen as one of the most important mechanisms of diversity maintenance contributing to stable coexistence of different species within communities. In this study, I examined whether four species of migrating shorebirds, dunlins (Calidris alpina), semipalmated sandpipers (Calidris pusilla), least sandpipers (Calidris minutilla) and short-billed dowitchers (Limnodromus griseus), segregate by time of passage, habitat use and foraging behavior at their major stopover in Delaware Bay during spring migration. I tested the prediction that most of the separation between morphologically similar species will be achieved by differential migration timing. Despite the high level of overlap along observed niche dimensions, this study demonstrates a certain level of ecological separation between migrating shorebirds. The results of analyses suggest that differential timing of spring migration might be the most important dimension along which shorebird species segregate while at stopover in Delaware Bay. Besides differences in time of passage, species exhibited differences in habitat use, particularly least sandpipers that foraged in vegetated areas of tidal marshes more frequently than other species, as well as short-billed dowitchers that foraged in deeper water more often than small sandpipers did. Partitioning along foraging techniques was less prominent than segregation along temporal or microhabitat dimensions. Such ranking of niche dimensions emphasizes significance of temporal segregation of migratory species – separation of species by time of passage may reduce the opportunity for interspecific aggressive encounters, which in turn can have positive effects on birds' time and energy budget during stopover period.

Top predators are relevant indicators of the ecological status of a system and can have a high impact on food webs. But top predators are difficult to include in network analyses because their biomass in ash free dry weight or carbon content ismissing. Regression equations were determined for the relationships between fresh weight and dry weight, ash free dryweight, carbon and nitrogen contents respectively for six of the most abundant bird species in theWadden Sea (Calidris canutus, Limosa lapponica, Haematopus ostralegus, Chroicocephalus ridibundus, Larus canus, Anas penelope) and harbor seals (Phoca vitulina). The relationships for all specieswere interpreted as linear through the origin. Carbon content vs. freshweight ratios for birds ranged from0.16±0.01 to 0.22±0.02. Carbon content vs. fresh weight ratio was 0.17± 0.02 on average for harbor seals. This work highlights that the biomass of top predatorswas often over- or underestimated in previous studies. The determined conversion factors will be useful for future studies to generate more realistic food web models.

Migration distances of shorebird species correlate with life history strategies. To assess age-specific migratory preparation and adult wing-molt strategies, we studied Western Sandpipers (Calidris mauri) and Semipalmated Sandpipers (C. pusilla) with different migration routes at the Paracas National Reserve in Peru, one of the most austral non-breeding areas for these sandpipers, from 2012 to 2015. Western Sandpipers breed near the Bering Sea, ~11,000 km from Paracas. Semipalmated Sandpiper populations at Paracas are a mixture of short-billed birds from western Arctic breeding sites, plus long-billed birds from eastern sites, ~8000 km distant. Adults of both species arrive in October with primary feathers already partially renewed so wing molt starts at sites further north. Semipalmated Sandpipers with longer bills completed wing molt later than shorter billed birds. Adults of both species prepared for migration in February and March. No juvenile Western Sandpipers prepared for migration, confirming the “slow” over-summering life history strategy of more southerly non-breeding populations. Juvenile Semipalmated Sandpipers showed bimodality in strategies. Most showed no migratory preparation, but, during three non-breeding periods, from 27% to 31% fattened, molted, and partially replaced outer primaries during the pre-migratory period. Juveniles with longer culmens were heavier and tended to have more alternate plumage. Juveniles that were partially molting primaries had longer culmens and more alternate plumage. Juvenile Semipalmated Sandpipers from eastern-breeding populations thus have a higher propensity for a fast life history strategy, and western birds a slow one, at this non-breeding site in Peru. Western-breeding Semipalmated Sandpiper populations thus resemble Western Sandpipers, suggesting a common, possibly distance-related, effect on life history strategy.

Habitat selection theory suggests that shorebirds should choose nest sites that maximize survival and fitness. We investigated how habitat, and proximity to conspecific or heterospecific nesting birds, was related to nest-site selection in American Golden-Plovers (Pluvialis dominica), Dunlin (Calidris alpina), Long-billed Dowitchers (Limnodromus scolopaceus), Pectoral Sandpipers (C. melanotos), Red Phalaropes (Phalaropus fulicarius), and Semipalmated Sandpipers (C. pusilla) in Barrow, Alaska, USA, between 2005 and 2012. We used remote-sensing data to link habitat information to used and unused nest sites, and we measured distances from nests to other nearby nesting shorebird neighbors. Results from an information-theoretic approach to identify best-approximating models indicated that all species selected nest sites on the basis of both habitat and social cues. Macroscale tundra moisture level within 50 m of the nest, which was closely associated with vegetation community, was an informative varia...

1. Behavioural variation within a species is usually explained as the consequence of individual variation in physiology. However, new evidence suggests that the arrow of causality may well be in the reverse direction: behaviours such as diet preferences cause the differences in physiological and morphological traits. 2. Recently, diet preferences were proposed to underlie consistent differences in digestive organ mass and movement patterns (patch residence times) in red knots (Calidris canutus islandica). Red knots are molluscivorous and migrant shorebirds for which the size of the muscular stomach (gizzard) is critical for the food processing rate. 3. In this study, red knots (C. c. canutus, n = 46) were caught at Banc d'Arguin, an intertidal flat ecosystem in Mauritania, and released with radio-tags after the measurement of gizzard mass. Using a novel tracking system (time-of-arrival), patch residence times were measured over a period of three weeks. Whether or not gizzard mass determined patch residence times was tested experimentally by offering 12 of the 46 tagged red knots soft diets prior to release; this reduced an individual's gizzard mass by 20-60%. To validate whether the observed range of patch residence times would be expected from individual diet preferences, we simulated patch residence times as a function of diet preferences via a simple departure rule. 4. Consistent with previous empirical studies, patch residence times in the field were positively correlated with gizzard mass. The slope of this correlation, as well as the observed range of patch residence times, was in accordance with the simulated values. The 12 birds with reduced gizzard masses did not decrease patch residence times in response to the reduction in gizzard mass. 5. These findings suggest that diet preferences can indeed cause the observed among-individual variation in gizzard mass and patch residence times. We discuss how early diet experiences can have cascading effects on the individual expression of both behavioural and physiomorphic traits. This emphasizes that to understand the ecological consequences of individual differences, knowledge of the environment during development is required.

Worldwide, most populations of migratory shorebirds are in jeopardy, none more so than those of the East Asian–Australasian Flyway (EAAF). In order to preserve these highly mobile species a detailed understanding of their use of feeding and resting sites along the flyway is required. In this study we used light-level geolocators and new analytical tools to reveal individual breeding locations and migration routes of 13 Sanderlings (Calidris alba) that spend their non-breeding season in South Australia. We then used these individual migration routes to identify the timing and location of important stopping areas and compared this with assessments based on resightings of leg-flagged birds and count data. During both northward and southward migration, Sanderlings were found to make extensive use of five main areas of the Chinese coastline, the Yellow Sea and the northern end of the Sakhalin Peninsula. Insights gained from the individual migration routes highlight inherent biases in using only count and resighting data to identify important feeding and resting sites along the Flyway. These findings suggest that data on individual movements may be crucial to effective conservation planning of shorebirds in the EAAF and elsewhere in the world.

Early detection is crucial to avoid threats from predators and competitors. Factors that affect threat detection have rarely been investigated in the context of food competition. I examined the ability to detect threats of displacement from feeding areas by competitors in flocks of staging Semipalmated Sandpipers (Calidris pusilla (L., 1766)). I predicted that targeted birds would be more likely to detect competitors attacking from the side or from the front rather than from behind because a blind area behind the head interferes with detection. Preening or sleeping birds in feeding areas might be less likely to detect attacks if such activities interfere with vigilance. If targeted birds maintain vigilance against attackers, attacks launched from farther away should be detected more frequently since more time is available for detection. As predicted, attacks were detected less often when launched from behind and more often when launched from farther away. The longest attacks were detected less often perhaps because birds relaxed their vigilance when neighbours were farther away. The ability to detect threats did not vary with targeted bird activity. Several factors influence the ability to detect threats from food competitors providing us with a novel context in which to investigate threat detection.

Vigilance can be targeted at predators or competitors, but there has been little work on the factors that affect vigilance aimed at competitors, which is known as social vigilance, and how it should be structured to detect and avoid conspecific threats. Social vigilance might be expected to play an important role in foraging groups with frequent conflicts over resources. I examined social vigilance in skimming semipalmated sandpipers, Calidris pusilla, which exploit minute prey at the surface of the substrate using a head-down position that leaves them vulnerable to aggressive displacement by neighbours. Attacks over resources occurred frequently in skimming sandpipers. In these groups, vigilance increased when neighbours were closer, suggesting that close neighbours posed a threat and that vigilance has a non-negligible social component in skimming groups. The negative exponential distribution best fitted the empirical distribution of intervals between successive vigilance bouts during skimming. This type of distribution implies that a bout of vigilance is initiated at the same rate regardless of the time spent head down in the current skimming bout, a feature that would prevent would-be attackers from targeting sandpipers at times of predictable vulnerability. This study shows that the occurrence of threats from within the group can promote randomness in the temporal organization of vigilance.

Calidris maritima (Purple Sandpiper) is a shorebird found along northern coasts of Europe and eastern North America during the winter. While its winter diet is well known in Europe, the only North American study examining diet included 5 individuals and suggested a narrow diet focused on Littorina spp. (periwinkles). We examined the diet of Purple Sandpipers wintering at several sites in Nova Scotia, Canada, during 2013, and found that the birds consumed a broad variety of items, though principally marine invertebrates, dominated by periwinkles and Mytilus edulis (Blue Mussel), but also many arthropods. Our study confirms the importance of mollusks in the diet of this species and also indicates that Purple Sandpipers in North America have a similar winter diet to those studied in Europe.

Many long-distance migratory shorebirds are threatened. Anthropogenic disturbance at roost sites on their non-breeding grounds might exacerbate other threats by leading to depletion of fat reserves and forcing birds away from traditional sites. We measured the response (occurrence of alarm flight and resettlement time) of roosting shorebirds knots (Calidris spp.) and sand plovers (Charadrius spp.) to anthropogenic and natural disturbances. Flight was the most common response (0.86 alarm flights h–1). The likelihood of an alarm flight was most strongly influenced by flock size and distance to the disturbance agent, smaller flocks closer to the agent being more likely to take flight. Sand plovers had shorter flight-initiation distances than knots but took longer to resettle after disturbance. Resettling duration was also influenced by time since arrival on the non-breeding grounds, being longest shortly after birds arrived. Energy budget models suggested that 10 alarm flights per day increased daily energy expenditure by 4.5–4.7% for knots and 7.5–7.8% for sand plovers. This may reduce energy reserves to levels below the threshold that can be replenished by normal intake rates and thus negatively affect survival or reproductive success. Increased disturbances may place additional and unsustainable pressures on populations that are already experiencing major declines.