Long-distance Migratory Shorebird Research Articles

Seasonal patterns and processes of migration in a long-distance migratory bird: energy or time minimization?

Optimal migration theory prescribes adaptive strategies of energy, time or mortality minimization. To test alternative hypotheses of energy- and time-minimization migration we used multisensory data loggers that record time-resolved flight activity and light for positioning by geolocation in a long-distance migratory shorebird, the little ringed plover, Charadrius dubius. We could reject the hypothesis of energy minimization based on a relationship between stopover duration and subsequent flight time as predicted for a time minimizer. We found seasonally diverging slopes between stopover and flight durations in relation to the progress (time) of migration, which follows a time-minimizing policy if resource gradients along the migration route increase in autumn and decrease in spring. Total flight duration did not differ significantly between autumn and spring migration, although spring migration was 6% shorter. Overall duration of autumn migration was longer than that in spring, mainly owing to a mid-migration stop in most birds, when they likely initiated moult. Overall migration speed was significantly different between autumn and spring. Migratory flights often occurred as runs of two to seven nocturnal flights on adjacent days, which may be countering a time-minimization strategy. Other factors may influence a preference for nocturnal migration, such as avoiding flight in turbulent conditions, heat stress and diurnal predators.

Movement ecology during non-breeding season in a long-distance migratory shorebird: are space use and movement patterns sex-biased?

Movement ecology during non-breeding season in a long-distance migratory shorebird: are space use and movement patterns sex-biased?

Individual foraging site fidelity persists within and across stopover seasons in a migratory shorebird, Numenius phaeopus (Whimbrel)

Abstract Site fidelity—returning repeatedly to the same site—can help many migratory species reduce uncertainty in their environment, especially when migratory stopover periods leave little time to explore and evaluate new habitat. Avian taxa, though, have shown wide variation in their levels of site fidelity during migration, and few studies have been able to examine individual-level fidelity at fine spatiotemporal scales. We used a high-resolution GPS tracking dataset of Numenius phaeopus (Whimbrel), a long-distance migratory shorebird, to assess levels of fidelity to specific foraging and roosting sites during migration, both within and between stopover seasons. We found that individuals are almost exclusively faithful to one shared roost site at night, but disperse to individual foraging territories during the day that overlap with each other by <20%. Individuals remain faithful to these distinct territories over time, on average shifting the center of their daily home ranges by <1.5 km within a single season, and overlapping with their previous season’s home range by 70% when they return during subsequent stopovers. Our findings reveal for the first time that a shorebird species exhibits fine-scale, individual foraging site fidelity during and between migratory stopovers—an important insight to inform effective conservation and management action.

GPS tracking analyses reveal finely-tuned shorebird space use and movement patterns throughout the non-breeding season in high-latitude austral intertidal areas

BackgroundLong-distance migratory birds spend most of their annual cycle in non-breeding areas. During this period birds must meet their daily nutritional needs and acquire additional energy intake to deal with future events of the annual cycle. Therefore, patterns of space use and movement may emerge as an efficient strategy to maintain a trade-off between acquisition and conservation of energy during the non-breeding season. However, there is still a paucity of research addressing this issue, especially in trans-hemispheric migratory birds.MethodsUsing GPS-tracking data and a recently developed continuous-time stochastic process modeling framework, we analyzed fine-scale movements in a non-breeding population of Hudsonian godwits (Limosa haemastica), a gregarious long-distance migratory shorebird. Specifically, we evaluated if these extreme migrants exhibit restricted, shared, and periodic patterns of space use on one of their main non-breeding grounds in southern South America. Finally, via a generalized additive model, we tested if the observed patterns were consistent within a circadian cycle.ResultsOverall, godwits showed finely-tuned range-residence and periodic movements (each 24–72 h), being similar between day and night. Remarkably, range-resident individuals segregated spatially into three groups. In contrast, a smaller fraction of godwits displayed unpredictable and irregular movements, adding functional connectivity within the population.ConclusionsIn coastal non-breeding areas where resource availability is highly predictable due to tidal cycles, range-resident strategies during both the day and night are the common pattern in a long-distance shorebird population. Alternative patterns exhibited by a fraction of non-resident godwits provide functional connectivity and suggest that the exploratory tendency may be essential for information acquisition and associated with individual traits. The methodological approach we have used contributes to elucidate how the composition of movement phases operates during the non-breeding season in migratory species and can be replicated in non-migratory species as well. Finally, our results highlight the importance of considering movement as a continuum within the annual cycle.

Assessment of contaminants, health and survival of migratory shorebirds in natural versus artificial wetlands – The potential of wastewater treatment plants as alternative habitats

The rapid destruction of natural wetland habitats over past decades has been partially offset by an increase in artificial wetlands. However, these also include wastewater treatment plants, which may pose a pollution risk to the wildlife using them. We studied two long-distance Arctic-breeding migratory shorebird species, curlew sandpiper (Calidris ferruginea, n = 69) and red-necked stint (Calidris ruficollis, n = 103), while on their Australian non-breeding grounds using an artificial wetland at a wastewater treatment plant (WTP) and a natural coastal wetland. We compared pollutant exposure (elements and per- and poly-fluoroalkyl substances/PFASs), disease (avian influenza), physiological status (oxidative stress) of the birds at the two locations from 2011 to 2020, and population survival from 1978 to 2019. Our results indicated no significant differences in blood pellet pollutant concentrations between the habitats except mercury (WTP median: 224 ng/g, range: 19–873 ng/g; natural wetland: 160 ng/g, 22–998 ng/g) and PFASs (total PFASs WTP median: 85.1 ng/g, range: <0.01–836 ng/g; natural wetland: 8.02 ng/g, <0.01–85.3 ng/g) which were higher at the WTP, and selenium which was lower at the WTP (WTP median: 5000 ng/g, range: 1950–34,400 ng/g; natural wetland: 19,200 ng/g, 4130–65,200 ng/g). We also measured higher blood o,o′-dityrosine (an indicator of protein damage) at the WTP. No significant differences were found for adult survival, but survival of immature birds at the WTP appeared to be lower which could be due to higher dispersal to other wetlands. Interestingly, we found active avian influenza infections were higher in the natural habitat, while seropositivity was higher in the WTP, seemingly not directly related to pollutant exposure. Overall, we found limited differences in pollutant exposure, health and survival of the shorebirds in the two habitats. Our findings suggest that appropriately managed wastewater treatment wetlands could provide a suitable alternative habitat to these migratory species, which may aid in curbing the decline of shorebird populations from widespread habitat loss.

Trends and population estimate of the threatened Buff-breasted SandpiperCalidris subruficolliswintering in coastal grasslands of southern Brazil

SummaryInformation about population sizes, trends, and habitat use is key for species conservation and management. The Buff-breasted SandpiperCalidris subruficollis(BBSA) is a long-distance migratory shorebird that breeds in the Arctic and migrates to south-eastern South America, wintering in the grasslands of southern Brazil, Uruguay, and Argentina. Most studies of Nearctic migratory species occur in the Northern Hemisphere, but monitoring these species at non-breeding areas is crucial for conservation during this phase of the annual cycle. Our first objective was to estimate trends of BBSA at four key areas in southern Brazil during the non-breeding season. We surveyed for BBSA and measured vegetation height in most years from 2008/09 to 2019/20. We used hierarchical distance sampling models in which BBSA abundance and density were modelled as a function of vegetation height and corrected for detectability. Next, we used on-the-ground surveys combined with satellite imagery and habitat classification models to estimate BBSA population size in 2019/20 at two major non-breeding areas. We found that abundance and density were negatively affected by increasing vegetation height. Abundance fluctuated five- to eight-fold over the study period, with peaks in the middle of the study (2014/15). We estimated the BBSA wintering population size as 1,201 (95% credible interval [CI]: 637–1,946) birds in Torotama Island and 2,232 (95% CI: 1,199–3,584) in Lagoa do Peixe National Park during the 2019/20 austral summer. Although no pronounced trend was detected, BBSA abundance fluctuated greatly from year to year. Our results demonstrate that only two of the four key areas hold high densities of BBSA and highlight the positive effect of short grass on BBSA numbers. Short-grass coastal habitats used by BBSA are strongly influenced by livestock grazing and climate, and are expected to shrink in size with future development and climatic changes.

Trace elements in relation to trophic ecology of long-distance migratory shorebirds and seabirds in West Africa

Shorebirds and seabirds are abundant predators in coastal habitats worldwide, relying upon a high diversity of benthic invertebrates and fish, respectively. While occupying different trophic guilds, they are differently exposed to element contamination entering the coastal food web. Therefore, these birds have been used as bioindicators of environmental contamination in marine ecosystems. We analysed the concentration of trace elements in blood samples of 16 shorebird and seabird migratory species in a major non-breeding site, the Bijagós Archipelago, in regard to their trophic ecology. Overall, our study shows low exposure of this bird community to toxic elements, except for Hg. Most species presented Hg burdens within the moderate toxicity threshold, but one species (Dunlin) presented values at a potential high Hg toxicity risk. We found a positive relationship between Se and Ni concentrations and δ15N values (a proxy for trophic level). In addition, a positive relationship was found between δ13C (a proxy for habitat characteristics) and Hg, Fe, Cu and Mn, while the opposite pattern was recorded for As. Differences were also shown for several trace elements between the two studied trophic guilds: concentrations of As, Pb and Se were higher in pelagic fish consumers (seabirds), whereas Cr, Fe and Sr burdens were higher in benthic invertebrate consumers (shorebirds). Although previous studies in the same site revealed very high concentrations of Cd and Pb in some of the prey species of shorebirds and seabirds (bivalves and fishes), values found in birds for these two elements suggest no toxicological risk. Thus, exposure to toxic elements is not currently a threat to coastal bird populations, namely those facing apparent local declines in Guinea-Bissau, one of the most important non-breeding quarters for of West Africa. Still, Hg burdens were high in some species, deserving further monitoring.

Flyway-scale GPS tracking reveals migratory routes and key stopover and non-breeding locations of lesser yellowlegs.

Many populations of long-distance migrant shorebirds are declining rapidly. Since the 1970s, the lesser yellowlegs (Tringa flavipes) has experienced a pronounced reduction in abundance of ~63%. The potential causes of the species' decline are complex and interrelated. Understanding the timing of migration, seasonal routes, and important stopover and non-breeding locations used by this species will aid in directing conservation planning to address potential threats. During 2018-2022, we tracked 118 adult lesser yellowlegs using GPS satellite tags deployed on birds from five breeding and two migratory stopover locations spanning the boreal forest of North America from Alaska to Eastern Canada. Our objectives were to identify migratory routes, quantify migratory connectivity, and describe key stopover and non-breeding locations. We also evaluated predictors of southbound migratory departure date and migration distance. Individuals tagged in Alaska and Central Canada followed similar southbound migratory routes, stopping to refuel in the Prairie Pothole Region of North America, whereas birds tagged in Eastern Canada completed multi-day transoceanic flights covering distances of >4000 km across the Atlantic between North and South America. Upon reaching their non-breeding locations, lesser yellowlegs populations overlapped, resulting in weak migratory connectivity. Sex and population origin were significantly associated with the timing of migratory departure from breeding locations, and body mass at the time of GPS-tag deployment was the best predictor of southbound migratory distance. Our findings suggest that lesser yellowlegs travel long distances and traverse numerous political boundaries each year, and breeding location likely has the greatest influence on migratory routes and therefore the threats birds experience during migration. Further, the species' dependence on wetlands in agricultural landscapes during migration and the non-breeding period may make them vulnerable to threats related to agricultural practices, such as pesticide exposure.

Australia as a global sink for the genetic diversity of avian influenza A virus.

Most of our understanding of the ecology and evolution of avian influenza A virus (AIV) in wild birds is derived from studies conducted in the northern hemisphere on waterfowl, with a substantial bias towards dabbling ducks. However, relevant environmental conditions and patterns of avian migration and reproduction are substantially different in the southern hemisphere. Through the sequencing and analysis of 333 unique AIV genomes collected from wild birds collected over 15 years we show that Australia is a global sink for AIV diversity and not integrally linked with the Eurasian gene pool. Rather, AIV are infrequently introduced to Australia, followed by decades of isolated circulation and eventual extinction. The number of co-circulating viral lineages varies per subtype. AIV haemagglutinin (HA) subtypes that are rarely identified at duck-centric study sites (H8-12) had more detected introductions and contemporary co-circulating lineages in Australia. Combined with a lack of duck migration beyond the Australian-Papuan region, these findings suggest introductions by long-distance migratory shorebirds. In addition, on the available data we found no evidence of directional or consistent patterns in virus movement across the Australian continent. This feature corresponds to patterns of bird movement, whereby waterfowl have nomadic and erratic rainfall-dependant distributions rather than consistent intra-continental migratory routes. Finally, we detected high levels of virus gene segment reassortment, with a high diversity of AIV genome constellations across years and locations. These data, in addition to those from other studies in Africa and South America, clearly show that patterns of AIV dynamics in the Southern Hemisphere are distinct from those in the temperate north.

Impact of rice paddy agriculture on habitat usage of migratory shorebirds at the rice paddy scale in Korea

Approximately 58 shorebird species, including endangered and threatened species, use various habitats while traveling on their long-distance migratory routes in the East Asian-Australasian Flyway (EAAF). Coastal rice paddies in midwestern Korea, which are located in the EAAF, serve as inland wetlands and provide important stopover sites for long-distance migratory shorebirds. We studied how shorebird population density is affected across periods, time since habitat formation, and field type, at the rice field scale. The shorebirds most frequently observed in rice paddies were, in order, black-tailed godwits (Limosa limosa), common greenshanks (Tringa nebularia), and wood sandpipers (T. glareola). Black-tailed godwits and wood sandpipers were affected by time since formation, field type, and water level, whereas field type affected common greenshanks. We propose that (1) flooding time, (2) shallow water level, (3) harrowed field type, and (4) 5–7 days of management intervals at paddy fields are important factors influencing shorebird species density, although all the factors did not influence common greenshank density. We propose that environmental characteristics derived from field management in rice paddies influence habitat use by migratory shorebirds. These factors need to be considered to systematically protect and manage shorebirds that use rice paddies as stopovers during their migration events.

Age-dependent timing and routes demonstrate developmental plasticity in a long-distance migratory bird.

Longitudinal tracking studies have revealed consistent differences in the migration patterns of individuals from the same populations. The sources or processes causing this individual variation are largely unresolved. As a result, it is mostly unknown how much, how fast and when animals can adjust their migrations to changing environments.We studied the ontogeny of migration in a long‐distance migratory shorebird, the black‐tailed godwit Limosa limosa limosa, a species known to exhibit marked individuality in the migratory routines of adults. By observing how and when these individual differences arise, we aimed to elucidate whether individual differences in migratory behaviour are inherited or emerge as a result of developmental plasticity.We simultaneously tracked juvenile and adult godwits from the same breeding area on their south‐ and northward migrations. To determine how and when individual differences begin to arise, we related juvenile migration routes, timing and mortality rates to hatch date and hatch year. Then, we compared adult and juvenile migration patterns to identify potential age‐dependent differences.In juveniles, the timing of their first southward departure was related to hatch date. However, their subsequent migration routes, orientation, destination, migratory duration and likelihood of mortality were unrelated to the year or timing of migration, or their sex. Juveniles left the Netherlands after all tracked adults. They then flew non‐stop to West Africa more often and incurred higher mortality rates than adults. Some juveniles also took routes and visited stopover sites far outside the well‐documented adult migratory corridor. Such juveniles, however, were not more likely to die.We found that juveniles exhibited different migratory patterns than adults, but no evidence that these behaviours are under natural selection. We thus eliminate the possibility that the individual differences observed among adult godwits are present at hatch or during their first migration. This adds to the mounting evidence that animals possess the developmental plasticity to change their migration later in life in response to environmental conditions as those conditions are experienced.

First records of prevalence and diversity of avian haemosporidia in snipe species (genus Gallinago) of Japan.

Migratory birds are important carriers of pathogens such as viruses, bacteria and protozoa. Avian haemosporidia have been detected from many wild birds of Japan, but the infection status of migratory birds and transmission area are still largely unknown. Gallinago snipes are long-distance migratory shorebirds, and five species migrate to or through Japan, including Latham's snipe which is near threatened. Haemosporidian parasites in four snipe species were investigated to understand the role of migratory birds in the transmission of avian haemosporidia. Namely, this study aimed: i) to investigate differences in parasite prevalence and related factors explaining infection likelihood among these migratory species, ii) to explore the diversity in haemosporidian lineages and possible transmission areas, and iii) to assess the possibility of morphological effects of infection. Blood samples were collected from snipes caught in central and southwest Japan during migration. Parasites cytb gene DNA were detected via PCR-based testing, and detected lineages were phylogenetically analyzed. Additionally, factors related to prevalence and morphological effects of infection were statistically tested. 383 birds from four Gallinago snipe species were caught, showing higher overall prevalence of avian haemosporidia (17.8 %) than reported in other wader species in previous studies. This high infection rate is presumably due to increased contact with vector insects, resultant of environmental preferences. The prevalence of Plasmodium spp. Was higher in Swinhoe's snipes, while Haemoproteus spp. Was higher in Latham's snipes. These differences are thought to be related to ecological factors including habitat use, distribution and migratory route. Six lineages detected from juveniles indicate transmission between the breeding and sampling area. Contrary to expectations, a direct link between morphological features and haemosporidian parasite infection were not detected. These findings provide valuable information for conservation of this endangered migratory bird group. Further studies linking biological and parasitological research are anticipated to contribute to conservational actions.

Plasticity in the hippocampal formation of shorebirds during the wintering period: Stereological analysis of parvalbumin neurons in Actitis macularius.

The number of parvalbumin neurons can be modified by social, multisensory, and cognitive stimuli in both mammals and birds, but nothing is known about their plasticity in long-distance migratory shorebirds. Here, in the spotted sandpiper (Actitis macularius), we investigated the plasticity of parvalbumin neurons of two brain areas during this species' wintering period at a lower latitude. We compared individuals in a nonmigratory rest period (November-January) and premigration (May-July) period. We used parvalbumin as a marker for counting a subpopulation of inhibitory neurons in the hippocampal formation (HF), with the magnocellular nucleus of the tectal isthmus (IMC) as a control area. Because the HF is involved in learning and memory and social interaction and the IMC is essential for control of head, neck, and eye movements, we hypothesized that parvalbumin neurons would increase in the HF and remain unchanged in the IMC. We used an optical fractionator to estimate cell numbers. Compared with the nonmigratory rest birds, parvalbumin neuron count estimates in the premigration birds increased significantly in the HF but remained unchanged in IMC. We suggest that the greater number of parvalbuminergic neurons in the HF of A. macularius in the premigration period represents adaptive circuitry changes involved in the migration back to reproductive niches in the northern hemisphere.

Genetic differentiation in an endangered and strongly philopatric, migrant shorebird

BackgroundPopulations living in fragmented habitats may suffer from loss of genetic variation and reduced between-patch dispersal, which are processes that can result in genetic differentiation. This occurs frequently in species with reduced mobility, whereas genetic differentiation is less common among mobile species such as migratory birds. The high dispersal capacity in the latter species usually allows for gene flow even in fragmented landscapes. However, strongly philopatric behaviour can reinforce relative isolation and the degree of genetic differentiation. The Southern Dunlin (Calidris alpina schinzii) is a philopatric, long-distance migratory shorebird and shows reduced dispersal between isolated breeding patches. The endangered population of the Southern Dunlin breeding at the Baltic Sea has suffered from habitat deterioration and fragmentation of coastal meadows. We sampled DNA across the entire population and used 12 polymorphic microsatellite loci to examine whether the environmental changes have resulted in genetic structuring and loss of variation.ResultsWe found a pattern of isolation-by-distance across the whole Baltic population and genetic differentiation between local populations, even within the southern Baltic. Observed heterozygosity was lower than expected throughout the range and internal relatedness values were positive indicating inbreeding.ConclusionsOur results provide long-term, empirical evidence for the theoretically expected links between habitat fragmentation, population subdivision, and gene flow. They also demonstrate a rare case of genetic differentiation between populations of a long-distance migratory species. The Baltic Southern Dunlin differs from many related shorebird species that show near panmixia, reflecting its philopatric life history and the reduced connectivity of its breeding patches. The results have important implications as they suggest that reduced connectivity of breeding habitats can threaten even long-distance migrants if they show strong philopatry during breeding. The Baltic Southern Dunlin warrants urgent conservation efforts that increase functional connectivity and gene flow between breeding areas.

Far eastern curlew and whimbrel prefer flying low - wind support and good visibility appear only secondary factors in determining migratory flight altitude

BackgroundIn-flight conditions are hypothesized to influence the timing and success of long-distance migration. Wind assistance and thermal uplift are thought to reduce the energetic costs of flight, humidity, air pressure and temperature may affect the migrants’ water balance, and clouds may impede navigation. Recent advances in animal-borne long-distance tracking enable evaluating the importance of these factors in determining animals’ flight altitude.MethodsHere we determine the effects of wind, humidity, temperature, cloud cover, and altitude (as proxy for climbing costs and air pressure) on flight altitude selection of two long-distance migratory shorebirds, far eastern curlew (Numenius madagascariensis) and whimbrel (Numenius phaeopus). To reveal the predominant drivers of flight altitude selection during migration we compared the atmospheric conditions at the altitude the birds were found flying with conditions elsewhere in the air column using conditional logistic mixed effect models.ResultsOur results demonstrate that despite occasional high-altitude migrations (up to 5550 m above ground level), our study species typically forego flying at high altitudes, limiting climbing costs and potentially alleviating water loss and facilitating navigation. While mainly preferring migrating at low altitude, notably in combination with low air temperature, the birds also preferred flying with wind support to likely reduce flight costs. They avoided clouds, perhaps to help navigation or to reduce the risks from adverse weather.ConclusionsWe conclude that the primary determinant of avian migrant’s flight altitude selection is a preference for low altitude, with wind support as an important secondary factor. Our approach and findings can assist in predicting climate change effects on migration and in mitigating bird strikes with air traffic, wind farms, power lines, and other human-made structures.

Upraising a silent pollution: Antibiotic resistance at coastal environments and transference to long-distance migratory shorebirds.

Large amounts of antibiotics from different sources have been released into coastal environments, especially in high human-populated areas, but comprehensive studies of antibiotic footprint in wildlife are scarce. Here we assess occurrence of antibiotic resistant bacteria (ARB) and antibiotic resistance gene (ARG) both in sediments and gut microbiota of a long-distance migratory shorebird species in two coastal wetlands at a sparsely-populated area in Pacific Patagonian coasts with contrasting potential antibiotic sources, especially from aquaculture. We found 62% of sediment samples showing ARB, and ARGs similarly occurring in sediments at both bays. However multi-resistant ARB were found only at sediments in the bay surrounding aquaculture operations. An 87% of cloacal bird samples showed at least one ARB, with 63% being multi-resistant and some of them with a high potential pathogenicity. ARGs were present in 46% of the samples from birds, with similar multi-resistant frequencies among bays. Besides specific differences mainly associated to antibiotics used in salmon aquaculture that boosted ARB in sediments, ARB and ARGs occurrence was overall similar at two bays with contrasting main human activities, in spite of being a comparatively low human-populated area. Therefore, our results reinforce the idea that the antibiotic footprint may be widespread at a global scale and can extend beyond the geographical influence of antibiotic sources, especially at coastal environments where migratory shorebirds act both as reservoirs and potential spreaders of antibiotic resistance.

A green wave of saltmarsh productivity predicts the timing of the annual cycle in a long-distance migratory shorebird

Understanding how migratory animals respond to spatial and temporal variation in habitat phenology is critical for identifying selection pressures and tradeoffs at different life history stages. We examined the influence of breeding habitat phenology on life history timing of the eastern willet (Tringa semipalmata semipalmata) across a latitudinal gradient of breeding sites on the east coast of North America. To describe migration and life history timing, we deployed light-level geolocators on willets at breeding sites in New Jersey, Massachusetts and Maine, USA and evaluated additional data on life history timing and migratory connectivity from previous studies, eBird and band recoveries. Willets from Nova Scotia to Georgia winter exclusively on the Atlantic coast of northern South America and share common stopover sites. The timing of wintering site departure, breeding site arrival, nesting and southbound departure was later for birds breeding at higher latitudes while the duration of all life phases was similar across sites. Regardless of latitude, nesting corresponded with a consistent stage of seasonal salt marsh biomass accumulation and with peak spring temperature acceleration (GDD jerk). Temperature acceleration and salt marsh biomass were closely correlated with each other across the 11° latitudinal gradient we examined and with the timing of nest initiation across the northern 6° of this gradient. For this northern 6° of latitude, these results suggest that the timing of migration and breeding events in the annual cycle of eastern willets is constrained by a phenological “green wave” of spring salt marsh productivity at breeding sites.

Disentangling abiotic and biotic mechanisms behind the formation of heterospecific Nearctic-Neotropical shorebird flocks

Defense, vigilance, and optimal foraging are frequently related to the formation of flocks in birds. Few studies concerning long-distance migrant shorebirds analyzed whether phylogeny and ecological similarities of species are associated with the formation of heterospecific flocks. Here, we explore (1) the niche conservatism theory, (2) the competition-relatedness hypothesis, and (3) the niche construction hypothesis to explain the formation of wintering Nearctic-Neotropical heterospecific shorebird flocks in the southeastern coast of Brazil. In the first, closely-related species keep their ecological traits over time. In the last two hypotheses, ecological dissimilar and distant-related species may coexist due to strong biotic interactions. Our results discard the influence of relatedness between species and/or phylogenetic filtering signals that could act in the formation of heterospecific flocks. Co-participation of species in flocks is explained by similarities in body weight and tarsus length, which invokes the niche construction hypothesis. Probably, some similar-sized and niche-constructing species are relocating in space and changing the environment that they experience to optimize individual capacity to flee from predators. From an ecological perspective, numerous phenotypically similar species with redundant roles could lead to greater resilience of the community under anthropogenic disturbances. From an evolutionary perspective, different species with similar phenotypes may diminish costs of activity matching and augment individual fitness.

Differences in Migration Timing along the Midcontinental Flyway in Sanderling (Calidris alba) from Three Gulf of Mexico Staging Areas

Although there is a clear link between early arrival on the breeding grounds and fitness in migratory birds, how winter and staging site use influence the timing of migration events prior to arrival at breeding areas is not well established. Therefore, there is a need to characterize the migration phenology of long-distance migratory birds. This study investigated the northbound migration timing of Sanderlings (Calidris alba) along the Central and Mississippi Flyways (i.e., the ‘Midcontinental Flyway’). Between 2015 and 2017, coded nanotags were attached to 120 Sanderlings in three staging areas in the USA portion of the Gulf of Mexico: North Padre and Bolivar Flats, Texas and sites in Louisiana. Individuals were then tracked northward using the Motus Wildlife Tracking System. Sanderling detections in more northern latitudes on northward migration were primarily in Saskatchewan (94%; n = 33), with only two individuals detected along the Atlantic coast. Sanderlings trapped in North Padre arrived later in Saskatchewan than individuals trapped in Bolivar Flats and Louisiana. Additionally, there was a negative association between Saskatchewan arrival timing and staging duration, such that later-arriving individuals from North Padre had significantly shorter staging durations and consequently departed from Saskatchewan at the same time as individuals originating from Bolivar Flats and Louisiana. These results provide new insight into the migration schedule of a declining long-distance migratory shorebird species and show how departure and arrival timing are linked across disparate staging sites.

Pro-inflammatory immune response is linked to wintering habitat in a migratory shorebird

AbstractMigratory shorebirds (Charadrii) show a strong dichotomy in their breeding and wintering strategies: Arctic-breeding species typically spend the wintering season in marine habitats, while more southerly breeding species tend to do so in freshwater habitats where pathogens and parasites, particularly vector-borne blood parasites, are generally more abundant. Thus, it has been hypothesized that the former group may reduce their investment in immunity, but experimental data supporting this hypothesis are lacking. Moreover, whether this contrasting habitat selection can shape investments in immunocompetence among populations within a species is uncertain. We experimentally tested the hypothesis that there is a significant association between habitat occupancy and the strength of a pro-inflammatory immune response in the Dunlin (Calidris alpina), a widely distributed long-distance migratory shorebird that breeds in (sub-)arctic areas and winters mainly, but not exclusively, in coastal habitats. Overwintering Dunlins occupying inland freshwater and marine habitats at a similar latitude were captured and acclimated under identical conditions in outdoor aviaries. After an acclimation period, they were challenged with phytohemagglutinin to assess the pro-inflammatory immune response and its associated energetic costs, measured by basal metabolic rate (BMR) and body mass changes. We found that freshwater Dunlins exhibited a higher (63%) pro-inflammatory immune response than marine Dunlins. Although this difference did not involve significant BMR changes, the time course of body mass response differed between freshwater and marine individuals. Our findings point to the existence of different pro-inflammatory immune responses and body mass adjustments associated with the wintering habitat. These intraspecific differences are likely due to population adaptation rather than phenotypic plasticity, where not only disease risk but also physiological adaptations to different salinity levels could play an important role.