The major histocompatibility complex (MHC) plays a central role in vertebrate adaptive immunity by encoding receptors that recognize pathogen-derived antigens. Migratory shorebirds, such as the Hudsonian Godwit (Limosa haemastica), encounter diverse pathogen landscapes across a wide range of habitats along their migratory routes. Therefore, migratory birds are expected to maintain a robust and effective immune system that minimizes the effects of infection without compromising their migration performance. We examined the genetic diversity of MHC class I exon 3 and MHC class IIB exon 2 across the species range. A total of 57 MHC-I and 13 MHC-IIB alleles were identified, with high polymorphisms observed in the peptide-binding regions (PBR). Signatures of positive selection were more pronounced in PBR sites from MHC-I than from MHC-IIB, suggesting stronger selective pressure from intracellular pathogens. In contrast, the relatively low allelic diversity and weaker selection signatures of MHC-IIB may reflect reduced exposure to extracellular pathogens. Despite broad geographic sampling, no evidence of an adaptive population structure was detected, indicating limited local adaptation and the likely influence of gene flow or neutral processes. Phylogenetic analyses revealed that some L. haemastica alleles clustered with those from closely related Scolopacidae species. These findings highlight the importance of pathogen-mediated selection in shaping MHC variation, providing valuable insights into the variability of a key group of adaptive immune genes in exceptional avian migratory species facing growing environmental pressure.

BACKGROUND: Many mobile organisms exhibit fidelity to specific foraging areas across seasons and years. Those that are both site faithful and habitat specialists may be particularly vulnerable to habitat loss and disturbance, as they may be less able to adjust their habitat use in response to environmental change. However, site fidelity can sometimes be a strategy to maximize efficiency via site familiarity rather than specialization, enabling more flexible habitat use at finer spatial scales. METHODS: We used high-resolution GPS tracking data, remote sensing imagery, and focal foraging observations to measure individual habitat specialization and its potential tradeoffs in Hudsonian Whimbrel (Numenius hudsonicus), a species that exhibits high individual foraging site fidelity in a spatiotemporally patchy intertidal environment during a month-long migratory stopover. RESULTS: We found that Whimbrel show low levels of habitat specialization and instead select habitat in proportion to its availability within their home range and its accessibility based on tidal inundation. Each habitat type, however, has associated tradeoffs between accessibility, foraging reward, and predation risk. Flexible habitat use is therefore likely a means to balance these tradeoffs. CONCLUSIONS: We posit that fidelity at the home range scale allows individuals to develop familiarity with how to balance habitat quality tradeoffs in a dynamic environment. While this inherent behavioral flexibility could buffer Hudsonian Whimbrel from the risks of environmental change, their reliance on low-lying intertidal habitats raises concerns as sea-level rise increasingly restricts the availability of their preferred foraging habitats. More broadly, investigating the interplay between fidelity and flexibility is critical for assessing how site-faithful species might cope with rapidly changing environments.

Gene flow affects the distribution of genetic variation of a species over time and thus can be crucial for a population's persistence and adaptive capacity. Given the importance of gene flow, it is key to understand the connectivity and genetic differentiation between populations of species with small and segregated breeding populations that are facing population declines, such as many long-distance migratory birds. In this study, we explored population structure in Hudsonian Godwits (Limosa haemastica) from two geographically distinct breeding areas in the North American sub-Arctic and two nonbreeding areas in South America using nuclear microsatellites. Despite being spatially and temporally segregated during most of the annual cycle, our results indicate no evidence of population differentiation between breeding populations, nor clustering between individuals from breeding and nonbreeding populations connected by migration. Considering the phenology of the species, godwits from both breeding populations could co-occur during southward migration and/or throughout the oversummering period, likely in the Las Pampas ecoregion of Argentina. As with many other long-distance migratory shorebirds, immature godwits stay in their nonbreeding areas until sexual maturity is reached, during which time they can explore, interact, and follow flocks of adults to different nonbreeding areas, thus increasing the chances of mixing between populations. This highlights the importance of recognizing the key role of early life period within the full life cycle of migratory birds for understanding their demography and evolutionary potential.

Addressing urgent conservation issues, such as the drastic declines of North American migratory birds, requires creative, evidence-based, efficient, and collaborative approaches. The abundance of over 50% of monitored North American shorebird populations has declined by over 50% since 1980. To address these declines, we developed a partnership of scientists and practitioners called the Shorebird Science and Conservation Collective (hereafter the collective). The collective was founded to translate the combined findings of shorebird tracking data into on-the-ground conservation action. With advice from an advisory group, the collective acts as an intermediary whereby dedicated staff collate and analyze data contributions from scientists to support knowledge requests from conservation practitioners. In its first three years, data contributions from 75 organizations include over 7.1 million shorebird observations forming movement paths of 3420 individuals representing 36 species tracked across the Americas and have informed 18 conservation projects spanning education, land and species management, land conservation, and policy requests. Others engaged in translational science from big data could consider similar knowledge-sharing models that prioritize usable data products, foster collaborative engagement between science experts and practitioners, build focused communities around topics or taxonomic groups, and employ a proof-of-concept phase to develop scalable solutions while making progress toward long-term funding to sustain impact. As the volume of scientific data continues to grow, intermediaries, such as the collective, can be vital liaisons to rapidly integrate and interpret research to support conservation action. Dedicated to the memory of Shiloh Schulte and his conservation achievements for shorebirds.

Climate change is transforming the Arctic and sub-Arctic at a pace that threatens many taxa with population declines and extinction. However, some habitats–such as muskeg bogs–can serve as climatic refugia and lessen the effects of a changing climate on the species that rely on them. Hudsonian Godwits (Limosa haemastica) are a species of migratory shorebird that utilizes the muskeg bogs of Alaska and Canada to breed. Our study focused on a muskeg bog in Beluga, Alaska, USA to see if it had changed from 2009 to 2023, if the availability of Godwit nests sites in the bogs changed in concert, and if Godwit nest survival was affected by any of these changes. We found that, overall, the bog dried and became more vegetated, with the proportional cover of graminoids, shrubs, and forbs all increasing during our study. Godwit nest sites also changed, with the proportion of shrubs and graminoids around nests increasing over time. Nonetheless, these changes did not negatively impact Godwit nest survival. Instead, nest survival increased 22

Extreme weather events are occurring more often, resulting in increasingly frequent mass mortality events for plants and animals. Identifying why individuals die during these events and their long-term consequences for populations can enable a mechanistic understanding of species' vulnerability to global change. Here we report on early-arriving purple martins (Progne subis)-a migratory songbird-that were killed at >50% of their breeding sites across two US states during a severe winter storm event in 2021. Victims exhibited substantial allelic differences from individuals sampled before and after the storm event. The surviving population suffered delayed breeding, reproductive failure and, in 2022, late breeding-ground arrival. Phenological trait values returned to the mean by 2024, yet the population may be unlikely to recover demographically until at least 2027. Purple martins are markedly declining in the region and signatures of past events suggest that frequent mass mortality events may be challenging their resiliency.

Young animals are often less mobile than adults, while also having high energetic demands. They may therefore be more vulnerable to local-scale changes in environmental conditions. In particular, when 1 sex must grow more rapidly than the other to achieve a larger adult size, that sex may experience especially dramatic reductions in growth and survival in the face of suboptimal environmental conditions. In order to investigate the flexibility of individuals in response to local-scale environmental variation during development, we studied the sex-specific growth, movement, and survival of Hudsonian Godwit (Limosa haemastica) chicks-a sexually dimorphic, precocial shorebird that breeds in the sub-Arctic and exhibits a male-skewed adult sex ratio. We found that female chicks-which must grow to a larger adult size-reached their maximum growth rates at a later age, but had similar growth rates to males before that and survived equally well to 21 days. We also found that, irrespective of sex, chicks had reduced movement rates when they were young and/or temperatures were cold, and only weakly increased their movement rates when invertebrate abundances remained low across an entire week. Early in life, godwit chicks may therefore be constrained from increasing their foraging efforts by local environmental conditions, forcing females to sustain higher growth rates late in the season past the local resource peak. Such sex-specific vulnerabilities could lead to lower early-life survival and, in turn, skewed adult sex ratios, which have important implications for population dynamics and persistence. We used an automated tracking system to follow Hudsonian Godwit chicks after they hatched. We found that chicks were largely unable to adjust their foraging effort to environmental conditions. Furthermore, despite their greater adult size, females did not grow faster than males early in life when their invertebrate prey was more abundant. Females must therefore grow faster during and after their third week of life, a period when local invertebrate abundance is rapidly declining.

Some staging regions support multiple groups of the same migratory species, each of which may use the region differently. Characterizing the ways in which separate groups use such regions can therefore help to identify vulnerabilities during this sensitive period of the annual cycle. The Prairie Pothole Region (PPR) is a massive wetland complex in the northern Great Plains of North America used by similar to 11 million shorebirds during migration. The PPR has been heavily modified by agriculture and is experiencing varied effects of global climate change, threatening the health of the shorebirds that rely on it. Here, we used 6 seasons of southbound tracking data of Tringa flavipes (Lesser Yellowlegs)-a long-distance migratory shorebird species with an estimated population decline of 63% over the last 4 decades-from 9 sites across their breeding range to explore differences in migratory behavior within this important staging region. We found that 75% of tracked individuals used the region during southbound migration, and that T. flavipes from different breeding sites detoured 110-875 km from their most direct migratory route to access the PPR. Individuals who arrived later stayed longer and made more stops within the region than those who arrived early. Individuals originating from different breeding sites also displayed spatial and temporal segregation within the region: T. flavipes from southwest and central Alaska relied heavily on the northwestern PPR, while those from Canada used the central and southeastern portions of the PPR. Finally, the timing of use varied among groups, but the southeastern PPR became increasingly important over the course of the southbound migratory window, as other wetlands likely dried out. Our study highlights the portions of the PPR of critical importance to migrating T. flavipes and the diversity of ways in which different groups from within the same species can use a single staging region. Shorebirds breeding at northerly latitudes display great diversity in migratory behavior both between and within species. We used GPS transmitters to track the southbound migration of 9 groups of Tringa flavipes (Lesser Yellowlegs) from across their breeding distribution, ranging from western Alaska to eastern Canada, over 6 years. Of the tracked individuals, 75% (n = 95) used the Prairie Pothole Region (PPR), an important staging region in the northern Great Plains of the USA and southern Canada. The groups of T. flavipes detoured 110-875 km from their most direct migration route to access the PPR, and used different portions of the PPR at different times. The northwestern and southeastern PPR were heavily used by T. flavipes from southwest Alaska in early and late migration, respectively. Maintaining shallow water on the landscape during those periods would likely increase the amount of critical shorebird habitat. Algunas regiones de escala albergan m & uacute;ltiples grupos de una misma especie migrante, cada uno de los cuales puede utilizar la regi & oacute;n de manera diferente. Caracterizar las formas en que distintos grupos utilizan estas regiones puede ayudar a identificar vulnerabilidades durante este per & iacute;odo sensible del ciclo anual. La Regi & oacute;n de Prairie Pothole (RPP) es un vasto complejo de humedales en las Grandes Llanuras del norte de Am & eacute;rica del Norte utilizado por similar to 11 millones de aves playeras durante la migraci & oacute;n. La RPP ha sido fuertemente modificada por la agricultura y est & aacute; experimentando diversos efectos del cambio clim & aacute;tico global, lo que amenaza la salud de las aves playeras que dependen de ella. Aqu & iacute; utilizamos 6 temporadas de datos de seguimiento durante la migraci & oacute;n hacia el sur de Tringa flavipes --una especie de ave playera migrante de larga distancia con una disminuci & oacute;n poblacional estimada del 63% en las & uacute;ltimas 4 d & eacute;cadas -- provenientes de 9 sitios a lo largo de su rango reproductivo, para explorar diferencias en el comportamiento migratorio dentro de esta importante regi & oacute;n de escala. Encontramos que el 75% de los individuos seguidos utiliz & oacute; la regi & oacute;n durante la migraci & oacute;n hacia el sur, y que los individuos de T. flavipes provenientes de distintos sitios reproductivos se desviaron entre 110 y 875 km de su ruta migratoria m & aacute;s directa para acceder a la RPP. Los individuos que llegaron m & aacute;s tarde permanecieron m & aacute;s tiempo y realizaron m & aacute;s escalas dentro de la regi & oacute;n que aquellos que llegaron temprano. Los individuos provenientes de distintos sitios reproductivos tambi & eacute;n mostraron segregaci & oacute;n espacial y temporal dentro de la regi & oacute;n: los del suroeste y centro de Alaska dependieron en gran medida de la RPP noroccidental, mientras que los provenientes de Canad & aacute; utilizaron las porciones central y sudoriental de la RPP. Finalmente, el momento de uso vari & oacute; entre grupos, pero la RPP sudoriental se volvi & oacute; cada vez m & aacute;s importante a lo largo del per & iacute;odo de migraci & oacute;n hacia el sur, a medida que otros humedales probablemente se secaban. Nuestro estudio resalta las porciones de la RPP de importancia cr & iacute;tica para los migrantes de T. flavipes y la diversidad de formas en que distintos grupos dentro de una misma especie pueden utilizar una & uacute;nica regi & oacute;n de escala.

We tested the effects of duty cycle on the estimation of metrics commonly used to summarize migration behaviour by sub-sampling high-resolution data from three shorebird species with different life-history characteristics-American Avocet Recurvirostra americana, Grey Plover (Black-bellied Plover) Pluvialis squatarola and Hudsonian Godwit Limosa haemastica. We found that metrics related to phenology (e.g. departure and arrival date, migration duration) were robust to varying GPS collection schedule (2-24 h between locations), and inference about metrics related to stopovers was generally reduced for devices collecting less frequent information, and these results were similar when considering short-, intermediate- and long-distance migrations. Where differences in estimates within a migration metric occurred, patterns varied among species and metrics, and linear models showed significant effects of duty cycle on the number of stopovers, stopover duration and within-stopover step length, in addition to a marginally significant effect on the proportion of time stopped over. Our results suggest that, for research questions related to stopover ecology, frequent data collection (e.g. multiple locations per day) should be prioritized in study design, but questions related to migration phenology can be addressed with less frequent information (e.g. one location per 24 h).

Population abundance and trend estimates are crucial to science, management, and conservation. Shorebirds, which are abundant in many coastal habitats and play important roles in coastal ecosystems, are facing some of the most dramatic population declines of any group of birds globally. However, accurate and up-to-date population estimates are lacking for most shorebird species. We thus conducted large-scale, simultaneous, and community scientist-led surveys of the Atlantic Coast of southern South America, stretching from central Brazil to Tierra del Fuego, to gather counts of shorebirds stratified by habitat that we combined with remote sensing analyses and two-step hurdle models that accounted for presence and abundance. Our objectives were to estimate shorebird densities by habitat, identify high-concentration areas, understand the environmental factors affecting their distributions, and provide population estimates for both Nearctic and Neotropical species. We counted a total of 37,207 shorebirds of 17 species and, from those counts, estimated that nearly 1.1 million shorebirds use the region's coastline. We found that the northern portion of the region was important for sandy beach specialists, while southern portions supported higher abundances of species that rely on intertidal mudflat and rocky habitats. We also found that shorebirds occurred in the highest densities in wetland habitats and that fewer shorebirds occupied areas that were further away from estuaries. Although not directly comparable, our results suggest the population sizes of the Nearctic species whose nonbreeding ranges are predominantly in southern South America may have declined substantially since previous estimates. At the same time, our study represents the first empirically derived population estimates for Neotropical breeding shorebird species and indicates that they are far more abundant than previously thought. Taken together, our results highlight the power of community scientists to carry out structured protocols at continental scales and generate critical data for a group of at-risk species.

Novel environments can induce fitness-reducing responses (i.e., maladaptive plasticity) that should be eliminated by selection via genetic compensation. Across an environmental gradient, genetic compensation may result in a cryptic form of trait variation known as countergradient variation, in which genetic changes oppose environmental effects on trait expression. We combined lab and field data to quantify maladaptive hematological responses to hypoxia and cold in deer mice (Peromyscus maniculatus) across their ∼4,000 m elevational range. In laboratory-raised mice native to low elevations, individuals increased their hemoglobin concentration and hematocrit in response to simulated high-elevation, a response that is maladaptive if unmitigated. In contrast, deer mice from high elevation increased hematocrit and hemoglobin to a lesser degree, consistent with genetic compensation. Unlike the predictions under complete genetic compensation, we observed a positive slope between hematological traits and elevation in the field, although this slope was lower than that observed in lowlanders in the lab. Our results suggest that deer mice have attenuated maladaptive hematological responses to high-elevation via genetic compensation that is incomplete, which has led to weak countergradient variation. We suggest this phenomenon is the result of a balance between positive selection for increased oxygen carrying capacity and antagonistic selection against elevated blood viscosity.

Migration strategy is a key behavioral characteristic guiding how migratory species time their annual cycles and use habitat. Understanding variation in migration strategy within and among species and individuals can be useful for understanding how birds navigate energetic trade-offs and designing or modifying conservation plans meant to benefit multiple species and life histories. We compared migration strategies among three migratory shorebird species with variable life history traits and short, medium, and long migration distances, respectively: American avocets (Recurvirostra americana), black-bellied plovers (Pluvialis squatarola), and Hudsonian godwits (Limosa haemastica). Avocets (short distance) exhibited the most within-species variation in migration duration, proportion of migration time spent at stopovers, and stopover duration. Plovers (medium distance) and godwits (long distance) showed less variation in these metrics, but godwits showed the most variation in the number of stopovers used. There were significant differences among species in migration distance, number of stopovers used, proportion of time stopped over, departure and arrival dates, and migration duration, but not mean stopover duration. We also found that avocets spent more time stopped over relative to migration distance than plovers or godwits, indicating that avocets showed the most energy-minimizing strategy of the three species. Our findings set the stage for future work assessing the effects of climate change and land use on characteristics associated with different migration strategies for additional migratory species.

Beach-nesting birds rely on predictable conditions for successful breeding, yet the effects of climatic events and beach morphology on nest placement remain underexplored. We examine how beach morphology influences nest placement and breeding success of least terns ( Sterna antillarum ) and snowy plovers ( Anarhynchus nivosus ) at Barra del Estero de Punta Banda, Baja California. Nest abundance along the northern beach is strongly linked to supratidal morphology. From 2018 to 2022, we monitored 411 least tern and 84 snowy plover nests. Of 162 nests with elevation data, 36% were successful and 11% failed due to flooding. We then examined nest placement effects, finding that across both species, nests located on berms had significantly higher survival (76%; 95% CI: 0.73–0.78) than those off berms (24%; 95% CI: 0–0.47). Furthermore, the highest nest densities were observed on dynamic profiles with prominent berms persisting across consecutive years. These berms extended approximately 40 m from the dune toe at elevations exceeding 2.8 m—approximately 0.5 m above the highest spring high-tide level. Although berms naturally erode in winter due to high-energy waves, they provide secure nesting platforms in summer that protect nests from flooding. Thus, the ability of the beach to rebuild wide berms after winter is crucial for nest success. As sea level rise and extreme weather alter beach morphology, species with greater flexibility in nest site selection may better find higher-quality nesting sites. Our research highlights the need for comprehensive solutions to mitigate the growing risk of nest flooding for beach-nesting birds.

With rapid environmental change, shifts in migration timing are vitally important for population stability in migratory species and have been widely documented. However, little remains known about how migrants make these shifts and what factors influence the utilization of these strategies, limiting assessments of their vulnerability to climate change. Hudsonian godwits ( Limosa haemastica ) are extreme long-distance migratory shorebirds that (i) have previously advanced their population-level migration timing and (ii) are sexually dimorphic. We combined over a decade of tracking data from one breeding population with a historical predictive model to assess ongoing shifts in migration timing and investigate potential sex-specific migration strategies. We found that irrespective of sex, godwit departure and arrival timing shifted 6 days later from 2010 to 2023. The population maintained an average migratory duration of 24 days and drove shifts in arrival timing entirely by changing their non-breeding-ground departure. Yet, we also found godwits arrived later than predicted by the historical model, indicating that conditions on the non-breeding grounds may constrain their ability to respond to changes on the breeding grounds. These results emphasize the need for a more holistic approach to assessing the vulnerability of migratory species and the adaptiveness of changes in migration timing.

Animal-borne trackers are commonly used to study bird movements, including in long-distance migrants such as shorebirds. Selecting a tracker and attachment method can be daunting, and methodological advancements often have been made by trial and error and conveyed by word of mouth. We synthesized tracking outcomes across 2745 dorsally mounted trackers on 37 shorebird species around the world. We evaluated how attachment method, power source, data retrieval method, relative tracker mass, and biological traits affected success, where success was defined as whether or not each tag deployment reached its expected tracking duration (i.e. all aspects succeeded for the intended duration of the study: attachment, tracking, data acquisition, and bird survival). We conducted separate analyses for tag deployments with remote data retrieval ('remote-upload tag deployments') and those that archived data and had to be recovered ('archival tag deployments'). Among remote-upload tag deployments, those that were a lighter mass relative to the bird, were beyond their first year of production, transmitted data via satellite, or were attached with a leg-loop harness were most often successful at reaching their expected tracking duration. Archival tag deployments were most successful when applied at breeding areas, or when applied to males in any season. Remote-upload tag deployments with solar power, satellite data retrieval, or leg-loop harnesses continued tracking for longer than those with battery power, other types of data retrieval, or glue attachments. However, the majority of tag deployments failed to reach their expected tracking duration (71% of remote-upload, 83% of archival), which could have been due to tracker failure, attachment failure, or bird mortality. Our findings highlight that many tag deployments may fail to meet the goals of a study if tracking duration is crucial. Using our results, we provide guidelines for selecting a tracker and attachment to improve success at meeting study goals.

BackgroundEcological barriers can shape the movement strategies of migratory animals that navigate around or across them, creating migratory divides. Wind plays a large role in facilitating aerial migrations and can temporally or spatially change the challenge posed by an ecological barrier, with beneficial winds potentially converting a barrier into a corridor. Here, we explore the role wind plays in shaping initial southbound migration strategy among individuals breeding at two sites along an ecological barrier.MethodsUsing GPS satellite transmitters, we tracked the southbound migrations of Short-billed Dowitchers (Limnodromus griseus caurinus) from two breeding sites in Alaska to nonbreeding sites in coastal Mexico. The breeding sites were positioned in distinct regions along an ecological barrier - the Gulf of Alaska. We investigated potential differences in migratory timing, wind availability, and tailwind support en route across the Gulf of Alaska between individuals breeding at the two sites.ResultsRoute choice and arrival timing to wintering sites differed markedly between the two breeding sites: individuals departing from the more westerly site left at the same time as those from further east but crossed the Gulf of Alaska farther west and arrived along the Pacific coast of Mexico an average of 19 days earlier than their counterparts. Dowitchers from both sites departed with slight tailwinds, but once aloft over the Gulf of Alaska, birds from the more westerly site had up to twelve times more tailwind assistance than birds from the more easterly one.ConclusionsThe distinct migration strategies and degree of wind assistance experienced by birds at these two breeding sites demonstrates how differences in wind availability along migratory routes can form the basis for intraspecific variation in migration strategies with potential carryover effects. Future changes in wind regimes may therefore interact with changes in habitat availability to influence migration patterns and migratory bird conservation.

Phenotypic plasticity has long played a central role in eco‐evolutionary theory, but it was not until 20 years ago that it was proposed that the term encompasses two distinct phenomena—developmental plasticity and phenotypic flexibility. While this terminology has since been adopted by some, the question of whether they are distinct phenomena remains contentious and they are both frequently lumped under the umbrella of ‘plasticity.’ Here, we treat the dichotomy between developmental plasticity and phenotypic flexibility as a hypothesis, put forth a set of predictions that follow from this hypothesis, and review the support for this hypothesis in the literature. We predict that, if they result from separate phenomena, developmentally plastic and phenotypically flexible traits should differ in: (1) the environmental context under which they evolve, (2) their mechanisms of regulation, (3) their costs of production, (4) how selection acts on them and (5) their influence on a population's evolutionary trajectory. In general, most evidence supports treating developmental plasticity and phenotypic flexibility as separate phenomena, but much remains to be learned, and few studies have specifically investigated their potential differences. In particular, explorations of their regulation, as well as the costs of trait production and reversal are needed. Given the hypothesized link between developmental plasticity, phenotypic flexibility and resiliency in the face of rapid environmental change, this is an urgent topic that will further our understanding of phenotypic evolution across environmental contexts. Read the free Plain Language Summary for this article on the Journal blog.

Beach-nesting birds rely on predictable and stable beach conditions for successful breeding, yet the complex impacts of climatic events, wave action, and variation in beach morphology on nest site selection remain underexplored. This study examines how variations in beach morphology influence nest site selection and breeding success in two conservation-priority species —the least tern (Sterna antillarum) and the snowy plover (Anarhynchus nivosus)—at Barra del Estero Beach, Baja California, Mexico. This beach, formed in the mid-to-late 1990s, likely due to alongshore sediment transport from neighboring beaches during energetic El Niño events, reveals that nest abundance correlates strongly with supratidal beach morphology. Both species exhibited significantly higher survival rates when nesting on berms compared to other areas. They presented highest nest densities on stable profiles featuring prominent berms extending approximately 40 m horizontally from the dune toe at elevations exceeding 2.8 m, 0.5 m above the highest spring high-tide level. While berms erode in winter due to high-energy waves, they serve as secure nesting platforms in summer, protecting nests from flooding. Thus, the ability of the beach to rebuild wide berms after the winter is crucial for nesting success. As sea-level rise and extreme weather events increasingly alter beach morphology, species with greater flexibility in nest site selection may more successfully identify higher-quality nesting sites. This research highlights the urgent need for comprehensive solutions to mitigate the growing risk of nest flooding in beach-nesting birds.

Identifying the migration routes and stopover sites used by declining species is critical for developing targeted conservation actions. Long-distance migratory shorebirds are among the groups of birds declining most rapidly, yet we frequently lack detailed knowledge about the routes and stopover sites they use during their hemisphere-spanning migrations. This is especially true for species that migrate through mid-continental regions in the Western Hemisphere. We therefore used satellite transmitters to track 212 individuals of 6 shorebird species during their southward migrations-Pluvialis dominica (American Golden-Plover), Limosa haemastica (Hudsonian Godwit), Tringa flavipes (Lesser Yellowlegs), Calidris subruficollis (Buff-breasted Sandpiper), C. melanotos (Pectoral Sandpiper), and Bartramia longicauda (Upland Sandpiper)-as they crossed the Amazon Basin of South America, a region from which reports of shorebird numbers are increasing but remain relatively rare. Our results make clear that the Amazon Basin provides stopover habitat for a large number of shorebirds: more than 74% of individuals tracked crossing the Amazon Basin stopped over in the region for an average of 2-14 days, with some spending the entire nonbreeding season there. All species selected stopover sites along the region's many rivers and lakes, while within stopover sites each species exhibited distinct habitat preferences. The timing of stopovers within sub-basins of the Amazon Basin also coincided with periods of low water, when the muddy, shallow water habitats preferred by most shorebirds are likely plentiful. Together, our results highlight the need for detailed investigations into shorebird abundance and distribution within the Amazon Basin, threats to shorebirds within particular subbasins, and links between shorebird conservation efforts and those targeting the myriad other species that inhabit this dynamic, hyper-diverse region. center dot Long-distance migratory shorebirds are declining worldwide. For many of these species, we lack essential information about their habitats throughout the year, including the stopover sites they use during migration.center dot In the Western Hemisphere, information is particularly lacking for the midcontinent of South America, a region that several shorebird species may cross during their southward migrations.center dot We examine satellite tracking data from 6 shorebird species to show that stops in the Amazon Basin are surprisingly common, occurring in more than 74% of southward migratory tracks.center dot Shorebirds selected stopover sites along rivers and lakes and exhibited distinct local-scale habitat preferences. These results highlight the need for detailed investigations into shorebird abundance and stopover site characteristics within the Amazon Basin, as well as potential links to broader conservation efforts. Identificar las rutas migratorias y los sitios de parada utilizados por las especies en declive es crucial para desarrollar acciones de conservaci & oacute;n espec & iacute;ficas. Las aves playeras migratorias de larga distancia est & aacute;n entre los grupos de aves que disminuyen m & aacute;s r & aacute;pidamente, pero con frecuencia carecemos de conocimientos detallados sobre las rutas y los sitios de parada que utilizan durante sus migraciones de magnitud hemisf & eacute;rica. Esto es especialmente cierto para las especies que migran a trav & eacute;s de las regiones medio-continentales del Hemisferio Occidental. Por lo tanto, utilizamos transmisores satelitales para rastrear a 212 individuos de 6 especies de aves playeras durante sus migraciones hacia el sur-Pluvialis dominica, Limosa haemastica, Tringa flavipes, Calidris subruficollis, C. melanotos y Bartramia longicauda-mientras cruzaban la cuenca amaz & oacute;nica de Am & eacute;rica del Sur, una regi & oacute;n en la cual los estudios sobre el n & uacute;mero de aves playeras est & aacute;n aumentando, pero siguen siendo relativamente raros. Nuestros resultados dejan claro que la cuenca amaz & oacute;nica proporciona h & aacute;bitat de parada para un gran n & uacute;mero de aves playeras: m & aacute;s del 74% de los individuos rastreados que cruzaron la cuenca amaz & oacute;nica se detuvieron en la regi & oacute;n durante un promedio de 2 a 14 d & iacute;as, y algunos pasaron toda la temporada no reproductiva all & iacute;. Todas las especies seleccionaron sitios de parada a lo largo de los numerosos r & iacute;os y lagos de la regi & oacute;n, mientras que dentro de los sitios de parada cada especie mostr & oacute; preferencias de h & aacute;bitat distintas. El momento de las paradas dentro de las subcuencas de la cuenca amaz & oacute;nica tambi & eacute;n coincidi & oacute; con per & iacute;odos de aguas bajas, cuando los h & aacute;bitats de aguas poco profundas y fangosas preferidos por la mayor & iacute;a de las aves playeras son probablemente abundantes. En conjunto, nuestros resultados destacan la necesidad de investigaciones detalladas sobre la abundancia y distribuci & oacute;n de las aves playeras dentro de la cuenca amaz & oacute;nica, las amenazas a las aves playeras dentro de subcuencas particulares, y los v & iacute;nculos entre los esfuerzos de conservaci & oacute;n de las aves playeras y aquellos dirigidos a la mir & iacute;ada de otras especies que habitan esta regi & oacute;n din & aacute;mica y de gran diversidad.

In many gregarious species, sex-specific differences can lead to significant variation in movement patterns and, consequently, to social and spatial segregation by sex within the population. Specifically, in several long-distance migratory shorebird species, reverse sexual dimorphism has been proposed as a driver of spatial segregation during the non-breeding season. Thus, sex-specific costs associated with space use during these stationary periods could differentially condition subsequent movement patterns between females and males in these species. Using satellite tracking technology, we analyzed the space use and movement patterns of a population of Hudsonian godwits (Limosa haemastica), a gregarious long-distance migratory shorebird, during the non-breeding season in Chiloé, Chile. We predicted that larger females would show more restricted movements and higher local site fidelity, while smaller males would be less competitive and more exploratory. Most individuals exhibited restricted space use (i.e., a home range), while a smaller fraction showed exploratory movements leading to a nomadic movement pattern. Most of these nomadic individuals subsequently oversummered in Argentina rather than migrating back to breeding areas. Contrary to our main prediction, none of the observed movement patterns were sex-biased. Recent evidence suggests that female and male godwits access prey of different sizes within the same foraging sites on Chiloé. Thus, in accordance with our results, and supported by recent additional findings, resource-partitioning within the same foraging patches could reduce interference competition between the sexes by offsetting the competitive advantage associated with the reversed sexual dimorphism of females over males. Finally, we propose these sex differences in foraging strategies could be advantageous for gregarious migratory shorebird populations that show strong connectivity and high site fidelity during and between non-breeding seasons. Size differences between sexes in migratory birds may result in different energetic requirements and, consequently, different movement patterns. Many migratory shorebirds exhibit reverse sexual dimorphism, and evidence suggests temporal and spatial sex-differences in space use and movement patterns in these species. We tested whether space use and movement patterns could be sex-biased in Hudsonian godwits (Limosa haemastica), a long-distance migratory shorebird with reverse sexual dimorphism, during the non-breeding season. We found no evidence that space use and movement patterns differed between sexes. We found that individuals exhibited two clear movement patterns: range-residency and nomadism. We propose that godwits likely employ sex-specific foraging strategies to exploit the same resource within the same space, consequently minimizing interference competition. We also suggest that the contrast between movement patterns may be the result of factors such as experience, physiological state, and external environmental conditions, rather than sex.