Worldwide, humans have altered ecosystems not only by reducing and changing the distribution of resources but also by providing new foraging opportunities to wildlife. However, little is known about the early-life development and maintenance of new foraging behaviours, which are crucial for species to adapt to human-induced environmental changes. Using a longitudinal global positioning system (GPS)-tracking dataset from 71 adult and 147 juvenile white storks (Ciconia ciconia) tracked for up to 6 years, this study investigates shifts in the exploitation of landfill resources during ontogeny and explores whether selective survival, within-individual improvements or both shape the emergence of this behaviour. Landfill use was found to increase with age. From their second year of life onwards, white storks visit landfills more often than in their first year, forage more in areas with abundant organic waste and reduce their foraging energy expenditure. Overall, this study reveals that the age-related increase in the use of anthropogenic food sources is driven primarily by within-individual improvements operating most strongly in early life, rather than by selective survival of individuals that most frequently and proficiently use landfill sites. As more species rely on anthropogenic food subsidies, this work highlights how opportunistic species cope with and adapt to human-driven environmental change, influencing individual lifetime decisions and potentially impacting population dynamics.

Environmental changes, including habitat loss and fragmentation in combination with climate change, have increased population reliance on protected areas (PAs) while also requiring individuals to adapt to changing local conditions or search for refugia when conditions deteriorate. Microclimate refugia within PAs may be critical for allowing species to persist when exposed to extreme thermal conditions, yet the availability of microclimate refugia and the ability of PAs to protect species from extremes has rarely been considered. We GPS-tracked 47 little bustards (Tetrax tetrax) in the Iberian Peninsula in 2009-2019, to understand their micro-scale climate and habitat use in the warmest period of the year, the post-breeding season. We compared post-breeding conditions at locations used in that period with those not used after breeding. We found that increasing temperature may reduce site suitability, while sites with greater microclimate refugia availability were more likely to be used by little bustards post-breeding. Although dispersed shrubs may provide micro-refugia, dense shrubby patches were avoided. While almost 63 % of the breeding locations were in PAs, only under 7 % of all post-breeding locations were within these key conservation areas, showing this species is not well protected across its life cycle. We assessed the impact of expected increasing temperatures from climate change scenarios and found that up to 15 % of currently used locations are predicted to become unsuitable, including those falling within PAs. Habitat management strategies should maintain landscapes with diverse characteristics that may provide shelter from extreme temperatures, such as scarce patches of low-density shrubs.

AimAnthropogenic climate change has increasingly been identified as a major threat to global biodiversity. However, the extent of this threat is likely to be uneven across species, due to differences in life histories or exposure to environmental change. The range of climatic conditions a species experiences across its range extent, known as the realised climatic niche, may be an indicator of species resilience to climate change. Species with large range extents, occurring across diverse climatic conditions, are expected to be less affected by climate change due to lower physiological constraints and tolerance to a wider range of climates. However, this may not be the case if local populations are adapted to specific environmental conditions. In this study, we investigate whether the extent of the species' realised climatic niche, also known as the climatic niche breadth, is linked to their long-term population trends.LocationEurope.TaxonBirds.MethodsWe extract climate data across the breeding-only and resident ranges of 159 European bird species and use an ordination method to produce a representation of the species climatic niches. We then relate the niche breadth of each species to their range area and incorporate this relationship, along with the species' diet, main habitat type, migratory status and average body mass, to investigate their relationship with the species long-term population trend.ResultsSpecies with small range areas showed larger variation in climatic niche breadth than species with larger ranges. For species with similar range areas, those with broader climatic tolerance were less likely to be declining than those with narrow climatic niches.Main ConclusionsThese findings can help us understand the threats associated with climate change and allow for rapid assessment of the importance of climatic factors on population trends, providing an invaluable tool for targeting habitat conservation.

Human-induced environmental changes are changing the migration patterns of birds worldwide. Species are adjusting migration timing, shortening and diversifying migratory routes or even transitioning towards residency. While the ultimate causes driving changes in migratory patterns are well established, the underlying mechanisms by which migratory species adapt to environmental change remain unclear. Here, we studied the mechanisms driving the recent and rapid loss of migratory behaviour in Iberian white storks Ciconia ciconia, a long-lived and previously fully migratory species through the African-Eurasian flyway. We combined 25 years of census data, GPS-tracking data from 213 individuals (80 adults and 133 first-year juveniles) tracked up to 7 years and whole-genome sequencing to disentangle whether within- (phenotypic flexibility) or between- (developmental plasticity or microevolution, through selection) individual shifts in migratory behaviour over time explain the observed population-level changes towards residency. Between 1995 and 2020, the proportion of individuals no longer migrating and remaining in Southern Europe year-round increased dramatically, from 18% to 68-83%. We demonstrate that this behavioural shift is likely explained by developmental plasticity. Within first-year birds, 98% crossed the Strait of Gibraltar towards their African wintering grounds, in Morocco or Sub-Saharan Africa. However, the majority shifted towards a non-migratory strategy as they aged-the proportion of migrants decreased to 67% and 33%, in their second and third year of life, respectively. Supporting these findings, only 19% of GPS-tracked adults migrated. We did not find evidence of phenotypic flexibility, as adults were highly consistent in migratory behaviour over multiple years (only 3 individuals changed strategy between years, out of 113 yearly transitions), nor of selection acting on genetic variation, since genomes of adult migrants and residents are essentially undifferentiated and we did not find evidence of selective sweeps in resident birds. Our results suggest that through developmental plasticity, traits that are plastic during specific windows of development become fixed during adulthood. Thus, inter-generational shifts in the frequency of migratory and non-migratory young individuals could drive population changes in migratory behaviour. This can provide a mechanism for long-lived migratory birds to respond to rapid human-driven environmental changes.

European steppe birds are facing unprecedented declines, positioning among the most threatened bird groups. We provide a comprehensive review and synthesis of the available knowledge on Western European (WE) steppe birds, focusing on their ecology, functional traits, population range trends and major threats. Using an expert-based participatory approach, we first created a consensual list of 37 WE species and reviewed the current knowledge on these key topics. Although 67.6 % of species show declining population ranges, only 18.9 % are classified as Endangered or Vulnerable according to the European IUCN Red List. Notably, several species exhibit range contractions over 5 % yet remain listed as Least Concern, indicating a need for re-evaluation based on the most up-to-date data. Threatened species have distinct functional traits compared to non-threatened species, typically being sedentary, large-bodied, long-lived, and exhibiting ground-foraging and ground-nesting behaviours. This highlights the potential for functional diversity loss if threatened species become extinct. Species experiencing the greatest range contractions share many of these traits or exhibit arboreal or aerial lifestyles, carnivorous diets and partial to fully migratory behaviours. Experts identified land use change and human-caused mortality as the main threats, followed by pollution and climate change, although the effects of the latter remain poorly understood for most species. Because significant knowledge gaps on climate and pollution effects remain for most species, these two threats should be the focus of future investigations. This synthesis enhances our understanding of the threats faced by WE steppe birds and provides guidance for prioritizing future research and conservation efforts.

The impact of anthropogenic debris on wildlife, particularly in marine environments, has garnered significant attention in recent years due to the severity of its effects. In terrestrial environments, the incorporation of human-derived materials into bird nests is well documented, yet most studies primarily focused on quantifying their prevalence rather than systematically examining their direct impacts, particularly on entanglement mortality. This study investigates the use of anthropogenic nest materials (ANMs) by a long-lived bird species and their impact on nestling mortality. Over four years, we photographed 568 white stork (Ciconia ciconia) nests to quantify ANMs and nestling mortality, while in 2023, we monitored 93 nests weekly from hatching to fledging to identify vulnerable developmental stages and high-risk materials. Habitat characteristics and proximity to landfill sites were analysed to infer ANM sources. ANMs were present in 91% of nests, with ropes-the main cause of entanglement-found in 42%. Entanglements, often fatal due to injuries such as necrosis and limb loss, were recorded in nearly one-third of the nests, affecting 12% of all nestlings. Most entanglements occurred in early nestling stages (mean age: 2 weeks +/- 1.38), highlighting that such fatalities may go undetected without early monitoring of nests. Entanglement risk increased with the number of ropes in the nests which were associated with agricultural areas. Baler twine, a slow degrading polypropylene rope used in agriculture, accounted for 63% of entanglements. This study reveals the widespread use of ANMs, their harmful effects on terrestrial birds, and the urgent need to mitigate baler twine pollution through management actions that minimise the impacts on the species affected by ANMs.

Accurately predicting species' responses to anthropogenic climate change is hampered by limited knowledge of their spatiotemporal ecological and evolutionary dynamics. We combine landscape genomics, demographic reconstructions, and species distribution models to assess the eco-evolutionary responses to past climate fluctuations and to future climate of an Afro-Palaearctic migratory raptor, the lesser kestrel (Falco naumanni). We uncover two evolutionarily and ecologically distinct lineages (European and Asian), whose demographic history, evolutionary divergence, and historical distribution range were profoundly shaped by past climatic fluctuations. Using future climate projections, we find that the Asian lineage is at higher risk of range contraction, increased migration distance, climate maladaptation, and consequently greater extinction risk than the European lineage. Our results emphasise the importance of providing historical context as a baseline for understanding species' responses to contemporary climate change, and illustrate how incorporating intraspecific genetic variation improves the ecological realism of climate change vulnerability assessments.

current biodiversity crisis shows that many species struggle to cope with the drastic changes driven by human expansion, yet some thrive in human-altered environments. White Stork (Ciconia ciconia) populations have grown considerably in recent decades, due to their ability to exploit anthropogenic food waste. Thousands of storks now rely on landfills and rubbish dumps year-round, as feeding on anthropogenic subsidies reduces travelling and foraging times, thus lowering overall energetic costs. This steady food supply has altered movement patterns, enabling year-round nest use and influencing home-ranges and affecting breeding and non-breeding behaviours. This shift in the dietary regime has significantly impacted migratory behaviour, with an increasing number of storks wintering in Southern Europe, closer to their breeding grounds, or even abandoning migration entirely. Feeding on landfill waste improves body condition, reproduction and survival, influencing population dynamics and distribution. However, this behaviour may produce contrasting impacts that remain largely unquantified, by significantly increasing the risk of pathogen infections, poisoning and ingestion of foreign bodies, which can affect storks' health and survival. While reducing food waste remains a global challenge, understanding the ecological and evolutionary implications of human-provided food on White Storks is critical for conservation and addressing broader human-wildlife conflicts. Received 15 Jan 2025, accepted 29 Jan 2025. Waterbirds 47(4): 1-7, 2025

The benefits of low-intensity mixed livestock-crop farming systems for Mediterranean farmland biodiversity have been widely documented. However, little is known about the effects of farming specialisation, even though the European Union's Common Agricultural Policy (CAP) has promoted the replacement of mixed systems by specialised livestock and crop systems. We investigated how specialisation affects birds in open farmland of southern Portugal, by analysing spatial associations between farming systems, land uses, and birds’ species richness and occurrence. We found a dominant landscape gradient contrasting specialisation in either sheep or cattle. The sheep system was positively related to woodland/shrubland-related species, Galerida larks and Melanocorypha calandra, while the cattle system was negatively related to these species. The specialised crop system, when associated with olive groves (< 10 % of the area), was negatively related to fallow-related species, M. calandra and Calandrella brachydactyla and positively so to overall species richness and that of woodland/shrubland-related species. Land uses had strong effects on birds, regardless of the farming systems in which they were embedded. Fodders were positively related to woodland/shrubland- and cereal-related species, Emberiza calandra and Cisticola juncidis. Rainfed grain cereals were positively related to cereal-related species, C. juncidis and Coturnix coturnix. Pastures were positively related to fallows- and ploughed-related species, M. calandra, Tetrax tetrax, and Galerida larks. Results suggest that programs for grassland conservation should consider both farming systems and land uses. CAP should promote diversified farming systems with reduced livestock densities along with high-quality habitats for grassland birds like pastures, fallows, rainfed grain cereals and semi-natural features.

Human activities have altered the availability of resources for wildlife. Landfill sites now provide abundant and predictable anthropogenic food subsidies worldwide, sustaining increasing numbers of opportunistic species and shaping their foraging behaviour. However, although individuals may differ in their ability to use these resources, the factors influencing this variability within species are still poorly known. Using GPS data from 68 adult and 67 juvenile white storks, Ciconia ciconia, tracked during their premigratory periods between 2018 and 2020, we investigated whether age determines landfill attendance and the ability to compete for space and food. Additionally, using video recordings of 165 adults and 124 juveniles obtained in the 2020 premigratory period, we investigated whether age influences landfill foraging proficiency and dominance over resources. Adult storks visited landfills on 57% of the days, while juveniles only visited landfills on 29% of the days. There was strong competition for food at landfills, with adults exerting dominance over juveniles, foraging predominantly in areas with higher food availability and outcompeting juveniles in food acquisition. Juveniles had significantly lower food intake rates in the best foraging areas and showed less aggressiveness, being forced to use adjacent lower quality areas. Overall, juveniles had limited access to landfill resources, suggesting that landfill diet specialization is mediated by age-related improvements in foraging expertise and increased competitiveness developed during maturation. Thus, landfill use is shaping foraging strategies and species behaviour from an early age, with potential consequences for population dynamics.

Afforestation affects Mediterranean farmland biodiversity due to loss and fragmentation of grassland habitats. While the influence of landscape context and plantation edges on farmland bird responses to afforestation is well-documented, less is known about the influence of grassland vegetation height and how it interacts with afforestation to influence bird communities. Here, we examined how changes in grassland vegetation height affect bird responses to afforestation in a farmland region in southern Portugal, and how these are affected by plantation type and edge. This region has experienced afforestation with eucalyptus, pine and oak stands, agricultural intensification, and frequent dry periods. To capture local and landscape-level changes, we collected data in two periods (2005 and 2014-15). Grassland vegetation height varied between sampling periods, emerging as a key factor affecting changes observed. Ground-nesting and cereal-associated species increased in abundance with taller vegetation in 2014-15, while in 2005, with drier weather and shorter vegetation, the species associated with ploughed fields were more abundant. Vegetation height effects on bird assemblages depended on plantation type and distance to plantation edges. Farmland bird abundance, including ground -nesting and cereal crops -associated species, increased with taller vegetation, particularly near oak and pine plantations. Conversely, species associated with ploughed fields declined with taller vegetation, especially near eucalyptus plantations. Results highlight complex interactions between vegetation height, plantation type, and edge proximity shaping avian assemblages. This study supports the importance of field and landscape -level management with special focus on grassland vegetation height and landscape heterogeneity for preserving open -farmland birds in fast -changing Mediterranean farmland landscapes.

Unsustainable fossil fuel emissions have prompted a global shift towards renewable energy sources, such as wind. This has led to a strong expansion of wind power generation infrastructures, often conflicting with biodiversity conservation. Relatively large flying animals, such as birds and bats, have frequently been reported to collide with wind turbines, resulting in casualties that can depress population size and lead to local extinctions. Migratory species that move across continents through their year-round displacements may be especially at risk. We comprehensively assessed wind turbine exposure for a colonial migratory raptor of European conservation interest, the lesser kestrel Falco naumanni , based on the distribution and size of >1800 colonies and a large GPStracking dataset ( >350 individuals) for three distinct biogeographical populations (from Iberian, Italian, and Balkan peninsulas). 26 % of the European population has at least one wind turbine within the foraging areas around colony sites, Italian colonies being most at risk. The main European network of protected areas, the Natura 2000 network, failed to mitigate the potential negative impact of wind turbines on breeding populations. GPS-tracking revealed that exposure was negligible in the African non -breeding areas (Sahel region), particularly high during migration, and lower during breeding for Iberian and Balkan individuals but not for Italian ones. Different countries should prioritize different measures to mitigate collision risk with wind power generation infrastructures. This case study can be leveraged by conservationists and renewable energy stakeholders to mitigate conflicts between biodiversity conservation and expected wind energy infrastructure development in the near future.

Human-induced direct mortality affects huge numbers of birds each year, threatening hundreds of species worldwide. Tracking technologies can be an important tool to investigate temporal and spatial patterns of bird mortality as well as their drivers. We compiled 1704 mortality records from tracking studies across the African-Eurasian flyway for 45 species, including raptors, storks, and cranes, covering the period from 2003 to 2021. Our results show a higher frequency of human-induced causes of mortality than natural causes across taxonomic groups, geographical areas, and age classes. Moreover, we found that the frequency of human-induced mortality remained stable over the study period. From the human-induced mortality events with a known cause (n = 637), three main causes were identified: electrocution (40.5 %), illegal killing (21.7 %), and poisoning (16.3 %). Additionally, combined energy infrastructure-related mortality (i.e., electrocution, power line collision, and wind-farm collision) represented 49 % of all human-induced mortality events. Using a random forest model, the main predictors of human-induced mortality were found to be taxonomic group, geographic location (latitude and longitude), and human footprint index value at the location of mortality. Despite conservation efforts, human drivers of bird mortality in the African-Eurasian flyway do not appear to have declined over the last 15 years for the studied group of species. Results suggest that stronger conservation actions to address these threats across the flyway can reduce their impacts on species. In particular, projected future development of energy infrastructure is a representative example where application of planning, operation, and mitigation measures can enhance bird conservation.

Identifying when and where organisms are exposed to anthropogenic change is crucial for diagnosing the drivers of biodiversity declines and implementing effective conservation measures. Accurately measuring individual-scale exposure to anthropogenic impacts across the annual cycle as they move across continents requires an approach that is both spatially and temporally explicit-now achievable through recent parallel advances in remote-sensing and individual tracking technologies. We combined 10 years of tracking data for a long-distance migrant, (common cuckoo, Cuculus canorus), with multi-dimensional remote-sensed spatial datasets encompassing thirteen relevant anthropogenic impacts (including infrastructure, hunting, habitat change, and climate change), to quantify mean hourly and total accumulated exposure of tracked individuals to anthropogenic change across each stage of the annual cycle. Although mean hourly exposure to anthropogenic change was greatest in the breeding stage, accumulated exposure to changes associated with direct mortality risks (e.g., built infrastructure) and with climate were greatest during the wintering stage, which comprised 63% of the annual cycle on average for tracked individuals. Exposure to anthropogenic change varied considerably within and between migratory flyways, but there were no clear between-flyway differences in overall exposure during migration stages. However, more easterly autumn migratory routes were significantly associated with lower subsequent exposure to anthropogenic impacts in the winter stage. Cumulative change exposure was not significantly associated with recent local-scale population trends in the breeding range, possibly because cuckoos from shared breeding areas may follow divergent migration routes and therefore encounter very different risk landscapes. Our study highlights the potential for the integration of tracking data and high-resolution remote sensing to generate valuable and detailed new insights into the impacts of environmental change on wild species.

Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average offspring production has declined in recent decades, but considerable differences were found among species and populations. A total of 56.7% of populations showed a declining trend in offspring production (significant in 17.4%), whereas 43.3% exhibited an increase (significant in 10.4%). The results show that climatic changes affect offspring production through compounded effects on ecological and life history traits of species. Migratory and larger-bodied species experienced reduced offspring production with increasing temperatures during the chick-rearing period, whereas smaller-bodied, sedentary species tended to produce more offspring. Likewise, multi-brooded species showed increased breeding success with increasing temperatures, whereas rising temperatures were unrelated to reproductive success in single-brooded species. Our study suggests that rapid declines in size of bird populations reported by many studies from different parts of the world are driven only to a small degree by changes in the production of young.

Alternative migratory strategies can coexist within animal populations and species. Anthropogenic impacts can shift the fitness balance between these strategies leading to changes in migratory behaviors. Yet some of the mechanisms that drive such changes remain poorly understood. Here we investigate the phenotypic differences, and the energetic, behavioral, and fitness trade-offs associated with four different movement strategies (long-distance and short-distance migration, and regional and local residency) in a population of white storks (Ciconia ciconia) that has shifted its migratory behavior over the last decades, from fully long-distance migration toward year-round residency. To do this, we tracked 75 adult storks fitted with GPS/GSM loggers with tri-axial acceleration sensors over 5 years, and estimated individual displacement, behavior, and overall dynamic body acceleration, a proxy for activity-related energy expenditure. Additionally, we monitored nesting colonies to assess individual survival and breeding success. We found that long-distance migrants traveled thousands of kilometers more throughout the year, spent more energy, and >10% less time resting compared with short-distance migrants and residents. Long-distance migrants also spent on average more energy per unit of time while foraging, and less energy per unit of time while soaring. Migratory individuals also occupied their nests later than resident ones, later occupation led to later laying dates and a lower number of fledglings. However, we did not find significant differences in survival probability. Finally, we found phenotypic differences in the migratory probability, as smaller sized individuals were more likely to migrate, and they might be incurring higher energetic and fitness costs than larger ones. Our results shed light on the shifting migratory strategies in a partially migratory population and highlight the nuances of anthropogenic impacts on species behavior, fitness, and evolutionary dynamics.

Aim Migratory species rely on multiple ranges across the annual cycle, rendering them vulnerable to a wide range of spatially disparate anthropogenic threats. The spatial distribution of these threats will strongly influence the magnitude of their population-scale effects, but this has not been quantitatively assessed for most species. Location Europe, Central Asia, Western Asia, Africa. Time period Modern. Major taxa studied Aves. Methods We combined remote-sensed data and expert opinion to map 16 anthropogenic threats relevant to migratory birds across Europe, Africa and the Middle East - including the first spatially-explicit pan-continental assessment of relative hunting pressure. By combining the resulting composite threat maps with species range polygons and morpho-behavioural traits-based weightings (reflecting relative threat susceptibility), we created species-specific risk maps for 103 Afro-Palaearctic migratory birds breeding in Europe and evaluated how spatial threat vulnerability relates to long-term population trends. Results We found that greater vulnerability to direct mortality threats (including hunting pressure, infrastructure and nocturnal lights), especially in the non-breeding season, is associated with declining bird population trends. Main conclusions Our results emphasize the importance of spatially explicit approaches to quantifying anthropogenic drivers of population declines. Composite risk maps represent a valuable resource for spatial analyses of anthropogenic threats to migratory birds, allowing for targeted conservation actions.

Predation risk profoundly shapes how animals behave and is one of the main forces driving the formation or maintenance of groups. For some species, group living may be facultative, and individuals may live solitarily or aggregate with conspecifics or heterospecifics, but the advantages of each strategy are still poorly known. Here, we investigated whether a predominantly solitary breeding species, the European roller, Coracias garrulus, acquires antipredator benefits from nesting in mixed-species colonies dominated by lesser kestrels, Falco naumanni. We compared the risk-taking behaviour of solitary rollers and rollers breeding in colonies by conducting two experiments. First, we investigated rollers??? latency to resume incubation when presented with a novel object, and second assessed their latency to resume chick provisioning and their investment in mobbing behaviour towards a predator model. We additionally compared the breeding performance and nest predation rate of rollers in each social context (solitary versus colonial) using data from 300 breeding attempts across 6 years. We found that rollers breeding in colonies returned to their nests sooner during the presentation of both the novel object and the predator model and attacked the predator model less frequently than solitary rollers, suggesting they can use heterospecifics as cues in deciding whether it is safe to return to their nests. In addition, rollers in colonies suffered less nest predation than solitary ones, but this did not translate into a higher productivity. Future studies should investigate whether breeding in colonies provides other advantages to rollers, such as increased adult survival or fitness. ?? 2022 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Abstract Background Migration phenology is shifting for many long-distance migrants due to global climate change, however the timing and duration of migration may influence the environmental conditions individuals encounter, with potential fitness consequences. Species with asynchronous migrations, i.e., with variability in migration timing, provide an excellent opportunity to investigate how of the conditions individuals experience during migration can vary and affect the migratory performance, route, and destination of migrants. Methods Here, we use GPS tracking and accelerometer data to examine if timing of autumn migration influences the migratory performance (duration, distance, route straightness, energy expenditure) and migration destinations of a long-distance, asynchronous, migrant, the white stork (Ciconia ciconia). We also compare the weather conditions (wind speed, wind direction, and boundary layer height) encountered on migration and examine the influence of wind direction on storks’ flight directions. Results From 2016 to 2020, we tracked 172 white storks and obtained 75 complete migrations from the breeding grounds in Europe to the sub-Saharan wintering areas. Autumn migration season spanned over a 3-month period (July–October) and arrival destinations covered a broad area of the Sahel, 2450 km apart, from Senegal to Niger. We found that timing of migration influenced both the performance and conditions individuals experienced: later storks spent fewer days on migration, adopted shorter and more direct routes in the Sahara Desert and consumed more energy when flying, as they were exposed to less supportive weather conditions. In the Desert, storks’ flight directions were significantly influenced by wind direction, with later individuals facing stronger easterly winds (i.e., winds blowing to the west), hence being more likely to end their migration in western areas of the Sahel region. Contrastingly, early storks encountered more supportive weather conditions, spent less energy on migration and were exposed to westerly winds, thus being more likely to end migration in eastern Sahel. Conclusions Our results show that the timing of migration influences the environmental conditions individuals face, the energetic costs of migration, and the wintering destinations, where birds may be exposed to different environmental conditions and distinct threats. These findings highlight that on-going changes in migration phenology, due to environmental change, may have critical fitness consequences for long-distance soaring migrants.