Spring Migration Research Articles

Urban waste-water treatment plants as hotspots for birds : an environmental assessment highlights the role of a single dominant gull

Waste-water treatment plants (WWTPs) are still little explored in their ecological role. This work reports data obtained from standardized sampling for the two largest Italian WWTPs, to obtain seasonal patterns (late winter, spring, and autumn) of univariate diversity metrics in bird communities. The ecological conditions, linked above all to the high availability of water, with the presence of mud and trophic resources, and heterogeneous features (buildings, trees, and hedges), allow the presence of water-related and synanthropic bird species, using the site as a seasonal stopover and wintering sites. The large availability of biomass of invertebrates, linked to the sludge from the water-waste treatment plants, can provide an important trophic resource during spring migration. The richness, diversity and evenness did not differ significantly between the two plants analysed, both having comparable size and heterogeneity. The highest Simpson dominance values were recorded in autumn with species frequency concentrated in a few abundant species. Detrended Correspondence Analysis (DCA) shows a close association between the autumn period and the dominant Black-headed Gull (Chroicocephalus ridibundus), in both treatment plants, with possible implication on the spreading on zoonosis.

Stopover habitat use of coastal Pied Avocet revealed by satellite tracking and remote sensing technology

Stopover sites identification for migratory waterbirds is important in China’s coastal wetlands, which have experienced a massive loss of natural wetlands in recent decades. Taking the Pied Avocet (Recurvirostra avosetta), a common waterbird in China’s coastal zone as an example, our research focused on their stopover habitat use based on satellite tracking and remote sensing technology. Along the coast, a total of 6 critical stopover sites, duration of stay more than 14 days, were recognized during their 2022–2023 autumn and spring migrations of the 4 tagged individuals. The results showed that Pied Avocets used habitats close to the coastline and water source, at low elevation, and with sparse vegetation. They also had a certain tolerance for human interference. From the perspective of the land use and land cover type, the proportion (33.01 %) of artificial wetlands including paddy, salt pan, and mariculture has exceeded that (27.97 %) of natural wetlands such as bottomland, tidal flat, estuarine waters, and shallow water in the home ranges of the 6 stopover areas. The study emphasized that the habitat function of artificial wetland should be paid enough attention to while maintaining the natural wetland without further loss. In addition, habitat-oriented management suggestions were put forward for artificial wetlands. This study can provide data and technical support for the conservation and management of waterbirds stopovers, also having reference value for other species.

Trace element contamination in three shorebird species migrating through Delaware Bay, New Jersey: arsenic, mercury and selenium are increasing.

Many shorebird populations are declining, and contaminants may be partly contributing to the decline by interfering with feeding, migration, and breeding success. The goal of our study was to determine whether there was a temporal change in concentrations of trace elements of red knot (Calidris canutus rufa), sanderling (Calidris alba), and ruddy turnstone (Arenaria interpres) during spring migration in Delaware Bay, New Jersey, USA. We sampled blood to 1) determine levels of trace elements in 2019, 2) compare 2019 trace element levels with those from shorebirds in 2011-2012, and 3) examine variability in blood levels of trace elements among species. In 2019: 1) trace element levels were significantly different among species (except cadmium[Cd]), 2) Cd was lowest in all species, and arsenic (As) and selenium (Se) were highest, and 3) sanderlings had the highest levels of As and Se, and knots had the highest levels of chromium (Cr) and lead (Pb). Se was higher in these shorebirds than reported for other shorebirds from elsewhere. As, mercury (Hg), and Se increased significantly between 2011-2012 and 2019 in all three species. There were no significant temporal changes in Cd. Chromium (Cr) decreased in knots and sanderling. The temporal increases in As, Se, and Hg bear watching as they are toxic in vertebrates, and each can decrease the toxicity of the others. The data indicate that shorebirds can be bioindicators of changing trace element levels in estuaries, potentially providing early warning of increasing levels of As, Hg, and Se in the environment.

High-resolution spatiotemporal forecasting of the European crane migration

In this paper we present three different models to forecast bird migration. They are species-specific individual-based models that operate on a high spatiotemporal resolution (kilometres, 15 min-hours), as an addition to radar-based migration forecast models that currently exist. The models vary in complexity, and use GPS-tracked location, flying direction and speed, and/or wind data to forecast migration speed and direction. Our aim is to quantitatively evaluate the forecasting performance and assess which metrics improve forecasts at different ranges. We test the models through cross-validation using GPS tracks of common cranes during spring and autumn migration. Our results show that recordings of flight speed and direction improve the accuracy of forecasts on the short range (<2 h). Adding wind data at flight altitude results in consistent improvements of the forecasts across the entire range, particularly in the predicted speed. Direction forecasts are less affected by adding wind data because cranes mostly compensate for wind drift during migration. Migration in spring is more difficult to forecast than in autumn, resulting in larger errors in flight speed and direction during spring. We further find that a combination of flight behaviours – thermal soaring, gliding, and flapping – complicates the forecasts by inducing variance in flight speed and direction. Fitting those behaviours into flight optimisation models proves to be challenging, and even results in significant biases in speed forecasts in spring. We conclude that flight speed is the most difficult parameter to forecast, whereas flight direction is the most critical for practical applications of these models. Such applications could e.g., be prevention of bird strikes in aviation or with wind turbines, and public engagement with bird migration.

Differential responses to weather and land‐cover conditions explain spatial variation in winter abundance trends in a migratory bird of conservation concern

Abstract Effective conservation strategies for animal populations require knowledge of relationships between population dynamics and their environmental drivers. However, these processes often vary within animal populations, requiring site‐specific conservation planning. Given limited financial resources, identifying groups of sites with similar population dynamics can help practitioners efficiently implement conservation programs to larger areas. We evaluated spatial patterns and environmental drivers of wintering site trends in a migratory bird of conservation concern, the Greenland white‐fronted goose (Anser albifrons flavirostris). We used latent class analysis to identify trend patterns in 35 years of abundance data among 59 geographically discrete Greenland white‐fronted goose wintering sites. We developed a state‐space abundance model in a Bayesian framework to quantify the effects of weather and land‐cover conditions experienced throughout spring migration, summer breeding, autumn migration and wintering periods on variation in wintering site abundance. We identified two main patterns in Greenland white‐fronted goose abundance trends: northeastern wintering sites declined on average by 3% per year, while southwestern wintering sites declined on average by 14% per year. Differential responses to weather and habitat conditions likely explained variation among groups, as geese at southwestern wintering sites were more negatively affected by harsh weather conditions (e.g. low temperatures and high precipitation on breeding areas) and poor habitat conditions (i.e. low‐quality grasslands and croplands) on wintering areas. Future conservation efforts to improve the suitability and nutritional quality of agricultural areas, especially cereal croplands in autumn and early winter and grasslands in late winter and early spring, could potentially improve local habitat conditions, especially in the southwestern wintering sites where abundance declines were steepest. Synthesis and applications. We demonstrate the potential to delineate animal populations based on spatial patterns in population dynamics using long‐term abundance monitoring data, which are commonly the only available data for conservation practitioners. By grouping sites based on spatial patterns in local abundance trends, we can further test hypotheses about how these groups are differentially affected by changing environmental conditions. This information is important for informing efficient conservation planning over large areas when financial resources are limited.

Oxidative state is associated with migration distance, but not traits linked to flight energetics

Flight can be highly energy demanding, but its efficiency depends largely on flight style, wing shape and wing loading, and a range of morphological and lifestyle adaptations that can modify the cost of sustained flight. Such behavioural and morphological adaptations can also influence the physiological costs associated with migration. For instance, during intense flight and catabolism of reserves, lipid damage induced by pro‐oxidants increases, and to keep oxidative physiological homeostasis under control, the antioxidant machinery can be upregulated. Studies on the oxidative physiology of endurance flight have produced contradictory results, making generalization difficult, especially because multispecies studies are missing. Therefore, to explore the oxidative cost of flight and migration, we used samples collected during the breeding season from 113 European bird species and explored the associations of measures of antioxidant capacity (total antioxidant status, uric acid and glutathione concentration) and oxidative damage of lipids (malondialdehyde) with variables reflecting flight energetics (year‐round or specifically during migration) using a phylogenetic framework. We found that none of the traits predicting year‐round flight energy expenditure (flight style, wing morphology and flight muscle morphology) explained any measures of oxidative state. Our results suggest that birds endure their everyday flight exercise without or with low oxidative cost. However, oxidative damage to lipids and one component of the endogenous antioxidant system (uric acid), measured after the end of spring migration on breeding adult birds, increased with migration distance. Our results suggest that migration could have oxidative consequences that might be carried over to subsequent life‐history stages (breeding).

Home range sizes and nychthemeral habitat uses by the Northern Shoveler (Spatula clypeata) on prenuptial stopovers in Vendée marshes, western France

The wetlands of Marais breton (MB) and Marais poitevin (MP) on the French Atlantic coast are commonly used by several duck species, especially as stopover sites during the prenuptial migration. Understanding the ecological requirements of Anatidae at spring stopover sites is important to define appropriate management actions that might have a carry over effect on the subsequent reproduction success. This study focused on the Northern Shoveler (Spatula clypeata), a species that regularly visits the two marshes during spring and fall migrations and is highly dependent on freshwater invertebrates as the food resource. Fifteen Northern Shovelers were equipped with GPS/GSM tags and monitored during their stopover in both marshes in 2020 and 2021. The aims of the study were to understand the habitat use on stopover sites and relate home range (HR) size with characteristics of the feeding habitats (such as freshwater invertebrates’ density and diversity). The HR area of the studied individuals was mainly constituted of ponds in MB (83% of the HR) and wet meadows in MP (71% of the HR). The Northern Shovelers equipped with tag spent more than 72 consecutive hours in 31 wetlands, using them during the day, at night or all day. The diurnal visited sites were deep ponds that were sparsely vegetated and dominated by microcrustaceans, whereas the nocturnal visited sites were wet meadows or ponds with high aquatic vegetation cover and high invertebrate taxonomic diversity. The 31 described sites appeared to be rich in freshwater invertebrates, with no significant difference in invertebrate densities between the diurnal and nocturnal sites. HR sizes were highly homogenous between the two study sites (MB and MP), between sexes or between age classes. In conclusion, according to this study, an appropriate HR for the Northern Shoveler at spring stopover is 8.49 ± 5.95 km² (mean ± standard error).

Non-breeding conditions induce carry-over effects on survival of migratory birds

Identifying the processes that limit populations is a foundational objective of ecology and an urgent need forconservation. For migratory animals, researchers must study individuals throughout their annual cycles to determine how environmental conditions limit demographic rates within each period of the annual cycleand also between periods through carry-over effects and seasonal interactions.1,2,3,4,5,6 Our poor understanding of the rates and causes of avian migration mortality7 hinders the identification of limiting factors and the reversal of widespread avian population declines.8,9 Here, we implement new methods to estimate apparent survival (hereafter survival) during migration directly from automated telemetry data10 in Kirtland's Warblers (Setophaga kirtlandii) and indirectly from mark-recapture data in Black-throated Blue Warblers (S.caerulescens). Previous experimental and observational studies of our focal species and other migratory songbirds have shown strong effects of Caribbean precipitation and habitat quality on food availability,11,12,13,14 body condition,12,13,14,15,16,17,18,19 migration timing,11,12,15,16,20,21,22,23 natal dispersal,24,25 range dynamics,26 reproductive success,20,22,27 and annual survival.18,19,20,23,28,29,30,31 Building on this research, we test the hypotheses that environmental conditions during the non-breeding period affect subsequent survival during spring migration and breeding. We found that reduced precipitation and environmental productivity in the non-breeding period strongly influenced survival in both species, primarily by reducing survival during spring migration. Our results indicate that climate-driven environmental conditions can carry over to affect survival in subsequent periods and thus likely play an important role in year-round population dynamics. These lethal carry-over effects may be widespread and are likely magnified by intensifying climate change.

Migratory behaviour of Ipswich Sparrows during spring

Optimal migration theory predicts birds will follow migration strategies that minimize time, energy, or predation risk, and these strategies employ specific and conflicting behaviours. Many behaviours driving songbird strategies are relatively well known, however gaps remain, especially for spring migration. Here, we describe the behaviours of a short-distance migrant, the Ipswich Sparrow ( Passerculus sandwichensis princeps Maynard, 1872), during spring migration. We determined the start and end dates of migration, migratory duration, travel speed, distance per night, and stopover location and duration. We also examined whether behaviours differed by sex and age. Sparrows migrated between March and June, and took an average of 29.1 days at a speed of 7.2 ± 9.4 m/s (SD) to fly ∼1574 km to their breeding grounds. Sparrows flew approximately 100 km/night and made stopovers of &gt;7 days adjacent to ecological barriers. Males migrated before females, and behaviour did not differ with age. Overall, Ipswich Sparrows had a relatively slow travel speed and covered short distances each night consistent with efforts to minimize energy costs or predation risk. They had prolonged stopovers suggesting that they were also trying to minimize time. More work is required to determine which strategy sparrows may be using during spring migration.

Oceanographic conditions of spring migration of European anchovy as a factor of formation of its spawning stock in the Sea of Azov

The aim of the work is to determine the influence of sea water circulation and temperature on the formation of the spawning stock of anchovy in the Sea of Azov.Materials and methods: Fishery and biological data on the spawning stock of the Azov anchovy were collected in surveys and bioresources monitoring carried out by the Azov-Black Sea branch of the VNIRO («AzNIIRKH») in 2000–2021. Satellite sea level data were used in the analysis of sea water circulation. These data, as well as satellite information on sea surface temperature for March-June 2000–2021 for the north-eastern part of the Black Sea and the southern part of the Azov Sea were taken from the website of the Copernicus Marine Service information system. Graphical and statistical methods of analyzing multi-year changes in the data were used in the work. The novelty of the performed work lies in the study of oceanographic conditions of spring migration of anchovy to the Sea of Azov as factors determining the size of its spawning stock in this sea.Result: intensive growth of the spawning stock of anchovy in the Sea of Azov was observed in 2008, 2010 and 2011. This was facilitated by: predominance of north-western geostrophic currents in the north-eastern part of the Black Sea in April 2008–2011, weakening of the Azov currents in the Kerch Strait in April 2007–2010 and predominance of the Black Sea currents in May 2004–2012, Decrease in the meridional gradient of water temperature in the Kerch Strait in April 2007–2010.Practical significance: the possibility of using oceanographic information for April-May to predict the size of the spawning and commercial stock of anchovy in the Sea of Azov.

Records from Neotropical non-breeding grounds reveal shifts in bird migration phenology over six decades

Changes in the migration phenology of birds linked to global change are extensively documented. Longitudinal studies from temperate breeding grounds have mostly shown earlier arrivals in the spring and a variety of patterns during fall migration,1,2 yet no studies have addressed whether and how migration phenology has changed using data from the tropical non-breeding grounds. Understanding whether changes in migratory phenology are also evident in non-breeding sites is essential to determining the underlying causes of patterns documented in breeding areas. Using data from historical scientific collections and modern repositories of community science records, we assessed changes in the migration phenology of 12 Nearctic-Neotropical long-distance migratory birds in Colombia over six decades. We also explored whether shared breeding and non-breeding climatic niches explained variation in the phenological patterns observed among species. All species showed shifts in spring (range -37 to 9days from peak passage date) or fall (range -26 to 36days) migration, but patterns differed among species in ways partly attributable to shared breeding or wintering climatic niches. Our results, although not yet broadly generalizable, suggest that birds use cues to time their migration at their non-breeding grounds, which are most likely different to those they use on their breeding grounds. To better understand the effects of global change on biodiversity, exploring the underlying drivers of phenological changes with further research integrating more long-term datasets available through scientific collections and community science platforms should be a priority.

Spring migration strategies of Anas platyrhynchos (Mallard) necessitate individual time-energy trade-offs despite wintering origins or migratory destinations

Abstract Spring migration is hypothesized to be time-constrained because of competition for optimal nesting and brood-rearing sites. Therefore, individuals are predicted to minimize migration time to breeding destinations; however, migration strategies likely lie on a continuum based on wintering and stopover habitat quality, environmental conditions, or individual-level factors. In other words, individuals and wintering subpopulations may differentially prioritize time-energy trade-offs during migration depending on where they are from, when they leave, and where they are going. We tested these hypotheses by characterizing spatial and temporal variation in spring migration strategies in female Anas platyrhynchos (Mallards), using global positioning system (GPS) data from ~150 individuals captured across the Mississippi Alluvial Valley and Gulf Coast Chenier Plain, USA. We used principal components analysis to classify a series of migratory behaviors into distinct time- and energy-minimization migration strategies, and tested whether migration strategies were related to wintering origins (habitat quality or latitudinal differences influencing migration initiation), migratory destinations (resource predictability), and individual-level factors (age and body condition). Additionally, we estimated individual and wintering subpopulation space-use to identify geographic regions of high and overlapping use that may facilitate time- or energy-minimizing migration strategies. Our results indicated a gradient of time-minimization migration strategies but migration strategy was not influenced by wintering origins nor migratory destination. Instead, time-energy trade-offs manifested at the individual level with time-minimization depending on experience and body condition. We also revealed stopovers and migration corridors of continental importance for spring-migrating A. platyrhynchos and space-use therein suggested migration strategies varied spatially with increasing time-minimization behavior as A. platyrhynchos neared their breeding grounds. Future research should link migration strategies and settling patterns to demographic rates.

Sod farms drive habitat selection of a migratory grassland shorebird during a critical stopover period

Migratory shorebirds are one of the fastest declining groups of North American avifauna. Yet, relatively little is known about how these species select habitat during migration. We explored the habitat selection of Buff-breasted Sandpipers (Calidris subruficollis) during spring and fall migration through the Texas Coastal Plain, a major stopover region for this species. Using tracking data from 118 birds compiled over 4 years, we found Buff-breasted Sandpipers selected intensively managed crops such as sod and short-stature crop fields, but generally avoided rangeland and areas near trees and shrubs. This work supports prior studies that also indicate the importance of short-stature vegetation for this species. Use of sod and corn varied by season, with birds preferring sod in spring, and avoiding corn when it is tall, but selecting for corn in fall after harvest. This dependence on cropland in the Texas Coastal Plain is contrary to habitat use observed in other parts of their non-breeding range, where rangelands are used extensively. The species' almost complete reliance on a highly specialized crop, sod, at this critical stopover site raises concerns about potential exposure to contaminants as well as questions about whether current management practices are providing suitable conditions for migratory grassland birds.

Projected distribution shifts of resident monarch butterflies and consequences for migratory monarchs

The charismatic migratory populations of monarch butterflies have declined precipitously in North America. A contributing threat might be the expansion of winter breeding populations in the southern portions of their historical eastern and western summer breeding ranges. Recent research suggests individuals from winter breeding populations are prone to high parasite burdens, resulting in lower fitness compared to migratory counterparts. Temporal and spatial overlap between these individuals and migratory monarchs in both fall and spring mean that interbreeding and use of the same host plants could result in transfer of parasites, especially the debilitating neogregarine Ophryocystis elektroscirrha, increasing the parasite load in migrating populations. We aimed to predict how climate change could affect the distribution of winter breeding monarchs in North America. We used ecological niche modeling of monarch larval observations for winter and current climate data to predict the current and future distributions of winter breeding monarchs across North America. Our analyses predict up to a 38% and 160% increase and a 574 and 340 km northward shift in suitable area for winter breeding monarchs in response to climate change by 2100 for eastern and western migratory populations, respectively. Our results support concerns over potential risk of disease spread from resident monarchs to the migratory monarch populations. In both eastern and western migratory populations this is due to an increase in overlap between the resident population and the areas through which the migratory populations travel during fall and spring migrations. Our results support calls for controlling the spread of non-native tropical milkweed, as winter breeding monarchs depend on this plant for reproduction.

Evidence of longitudinal differences in spring migration strategies of an Arctic-nesting goose.

During spring, migratory birds are required to optimally balance energetic costs of migration across heterogeneous landscapes and weather conditions to survive and reproduce successfully. Therefore, an individual's migratory performance may influence reproductive outcomes. Given large-scale changes in land use, climate, and potential carry-over effects, understanding how individuals migrate in relation to breeding outcomes is critical to predicting how future scenarios may affect populations. We used GPS tracking devices on 56 Greater White-fronted Geese (Anser albifrons) during four spring migrations to examine whether migration characteristics influenced breeding propensity and breeding outcome. We found a strong longitudinal difference in arrival to the breeding areas (18 days earlier), pre-nesting duration (90.9% longer), and incubation initiation dates (9 days earlier) between western- and eastern-Arctic breeding regions, with contrasting effects on breeding outcomes, but no migration characteristic strongly influenced breeding outcome. We found that breeding region influenced whether an individual likely pursued a capital or income breeding strategy. Where individuals fell along the capital-income breeding continuum was influenced by longitude, revealing geographic effects of life-history strategy among conspecifics. Factors that govern breeding outcomes likely occur primarily upon arrival to breeding areas or are related to individual quality and previous breeding outcome, and may not be directly tied to migratory decision-making across broad scales.

Migratory herbivorous waterfowl track multiple resource waves during spring migration.

East Asian herbivorous waterfowl intensively use farmland in spring, next to their natural habitat. Accordingly, they might have expanded their migration strategy from merely tracking the green wave of newly emerging vegetation to also incorporating the availability of post-harvest agricultural seeds (here dubbed the seed wave). However, if and how waterfowl use multiple food resources to time their seasonal migration is still unknown. We test this migration strategy using 167 spring migration tracks of five East Asian herbivorous waterfowl species and mixed-effect resource selection function models. We found that all study species arrived at their core stopover sites in the Northeast China Plain after agricultural seeds became available, extended their stay after spring vegetation emerged and arrived at their breeding sites around the emergence of vegetation. At the core stopover sites, all study species used snowmelt as a cue to track seed availability, although smaller-bodied species tended to arrive later. At the breeding sites, swans tracked the onset of vegetation emergence and geese tracked the mid- or end phases of snowmelt. Our findings suggest that waterfowl track multiple resource waves to fine-tune their migration, highlighting new opportunities for conservation.

Shoreline Translocation during Road Expansion Was Successful for Most Waterbirds but Not for Waders

Coastal wetlands are one of the most threatened ecosystems due to, firstly, their relative rarity and, secondly, the strong human interest in these coastal sites for infrastructure development, and recreation. These coastal wetlands also serve as important migration stopover sites for a range of waterbirds. There is great international interest in mitigating the negative effects of human land development and in restoring degraded habitats. I evaluated the response of one waterbird community to the mitigation action implemented during road expansion in an important waterbird coastal habitat in central Norway. Using a novel mitigation method, the shoreline was moved seawards to allow space for a continued shoreline habitat and the extended road. By weekly monitoring the waterbird community during spring and autumn migration periods (n = 7 of each), I found similar biodiversity, evenness, and abundance of geese, dabbling ducks, diving ducks, gulls, and waders when data for the whole wetland were used. However, after construction waders were partially displaced from the zone closest to the road to a zone further away. For some groups of birds, shoreline translocation can be a fruitful mitigation action aiming to reduce the negative effects of infrastructure expansion in coastal areas.

Ultra-long-distance migration of the common Cuckoo (&lt;i&gt;cuculus canorus&lt;/i&gt;, cuculiformes, cuculidae) from Kamchatka to Namibia

The application of high-tech methods for tracking birds, primarily satellite telemetry, has made it possible in a relatively short time to reveal real migratory routes and wintering areas for many bird species. In the Common cuckoo, whose breeding range extends over a vast territory from Portugal to Kamchatka, the migratory routes and wintering grounds have been well studied for a number of European populations, while the migration of Asian populations of this species is still not so well studied. In this work, we analyze satellite telemetry data obtained from four adult males of the Common cuckoo caught in early June 2017 during the nesting period on the Kamchatka Peninsula near the town of Yelizovo. The autumn migration of these birds started in August to early September. They crossed the Sea of Okhotsk (more than 1 000 km) and, without staying for a long time in the Khabarovsk Region, stopped in China (Sichuan, Hebei, Heilongjiang provinces), where they remained for a long time, from 32 to 52 days, moving around this country until October to November. In southern China, all three surviving males changed their SW direction of migration to almost western and flew crossing Myanmar and Bangladesh to India, where they stopped over for 24–34 days until November 10th or 29th. Then the birds crossed the Arabian Sea in 2–3 days overcoming the huge body of water of about 3 000 km in width without stop to land on the African continent (Somalia). Further migration of Kamchatka cuckoos passed through the countries of East Africa such as Ethiopia, Kenya, Tanzania, Malawi, Zambia or Zimbabwe, where they stayed from 2 to 11 days. Finally, all three individuals reached wintering areas in December, first in Botswana, then in Namibia. Thus, the duration of autumn migration of Kamchatka cuckoos varied from 106 to 123 days. During this time, they overcame a record distance of 17,340 km for land birds. The spring migration of two birds started on April 19th or 26th next year. They flew back using a similar route as in autumn. One individual crossed the Arabian Sea in early May, the other from May 20th to 22nd. Having reached India, one bird almost the same day arrived to Bangladesh and then to China. The other one stayed on the Hindustan Peninsula for 11 days, this being much shorter than in autumn. Unfortunately, only one male reached the nesting area in Kamchatka (May 31st). Apparently, the other one either died or lost the transmitter in China. The survived male returned to its former nesting area with high accuracy, its transmitter emitted signals until July 10th. The spring migration took the birds much less time (42 days) than in autumn (106–123 days). Thus, we recorded an ultra-long total distance of autumn and spring migration for a land bird species of almost 34,000 km from Kamchatka to Namibia and back.

Persistent species relationships characterize migrating bird communities across stopover sites and seasons

Global migrations of diverse animal species often converge along the same routes, bringing together seasonal assemblages of animals that may compete, prey on each other, and share information or pathogens. These interspecific interactions, when energetic demands are high and the time to complete journeys is short, may influence survival, migratory success, stopover ecology, and migratory routes. Numerous accounts suggest that interspecific co-migrations are globally distributed in aerial, aquatic, and terrestrial systems, although the study of migration to date has rarely investigated species interactions among migrating animals. Here, we test the hypothesis that migrating animals are communities engaged in networks of ecological interactions. We leverage over half a million records of 50 bird species from five bird banding sites collected over 8 to 23 y to test for species associations using social network analyses. We find strong support for persistent species relationships across sites and between spring and fall migration. These relationships may be ecologically meaningful: They are often stronger among phylogenetically related species with similar foraging behaviors and nonbreeding ranges even after accounting for the nonsocial contributions to associations, including overlap in migration timing and habitat use. While interspecific interactions could result in costly competition or beneficial information exchange, we find that relationships are largely positive, suggesting limited competitive exclusion at the scale of a banding station during migratory stopovers. Our findings support an understanding of animal migrations that consist of networked communities rather than random assemblages of independently migrating species, encouraging future studies of the nature and consequences of co-migrant interactions.

Seasonal migration patterns of Siberian Rubythroat (Calliope calliope) facing the Qinghai–Tibet Plateau

BackgroundSmall songbirds respond and adapt to various geographical barriers during their annual migration. Global flyways reveal the diverse migration strategies in response to different geographical barriers, among which are high-elevation plateaus. However, few studies have been focused on the largest and highest plateau in the world, the Qinghai–Tibet Plateau (QTP) which poses a significant barrier to migratory passerines. The present study explored the annual migration routes and strategies of a population of Siberian Rubythroats (Calliope calliope) that breed on the north-eastern edge of the QTP.MethodsOver the period from 2021 to 2023, we applied light-level geolocators (13 deployed, seven recollected), archival GPS tags (45 deployed, 17 recollected), and CAnMove multi-sensor loggers (with barometer, accelerometer, thermometer, and light sensor, 20 deployed, six recollected) to adult males from the breeding population of Siberian Rubythroat on the QTP. Here we describe the migratory routes and phenology extracted or inferred from the GPS and multi-sensor logger data, and used a combination of accelerometric and barometric data to describe the elevational migration pattern, flight altitude, and flight duration. All light-level geolocators failed to collect suitable data.ResultsBoth GPS locations and positions derived from pressure-based inference revealed that during autumn, the migration route detoured from the bee-line between breeding and wintering grounds, leading to a gradual elevational decrease. The spring route was more direct, with more flights over mountainous areas in western China. This different migration route during spring probably reflects a strategy for faster migration, which corresponds with more frequent long nocturnal migration flights and shorter stopovers during spring migration than in autumn. The average flight altitude (1856 ± 781 m above sea level) was correlated with ground elevation but did not differ between the seasons.ConclusionsOur finding indicates strong, season-dependent impact of the Qinghai–Tibet Plateau on shaping passerine migration strategies. We hereby call for more attention to the unexplored central-China flyway to extend our knowledge on the environment-migration interaction among small passerines.