Paternal transmission of migration knowledge in a long-distance bird migrant

Mechanisms underlying the loss of migratory behaviour in a long-lived bird

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.

Social learning and culture in birds: emerging patterns and relevance to conservation

There is now abundant evidence for a role of social learning and culture in shaping behaviour in a range of avian species across multiple contexts, from migration routes in geese and foraging behaviour in crows, to passerine song. Recent emerging evidence has further linked culture to fitness outcomes in some birds, highlighting its potential importance for conservation. Here, we first summarize the state of knowledge on social learning and culture in birds, focusing on the best-studied contexts of migration, foraging, predation and song. We identify extensive knowledge gaps for some taxa but argue that existing evidence suggests that: (i) social learning and culture are taxonomically clustered and that (ii) reliance on social learning in one behavioural domain does not predict reliance across others. Together, we use this to build a predictive framework to aid conservationists in species-specific decision-making under imperfect knowledge. Second, we review evidence for a link between culture and conservation in birds. We argue that understanding which behaviours birds are likely to learn socially can help refine conservation strategies, improving the trajectories of threatened populations. Last, we present practical steps for how consideration of culture can be integrated into conservation actions including reintroductions, translocations and captive breeding programmes.This article is part of the theme issue 'Animal culture: conservation in a changing world'.

Selective disappearance based on navigational efficiency in a long-lived seabird

Whilst efficient movement through space is thought to increase the fitness of long-distance migrants, evidence that selection acts upon such traits remains elusive. Here, using 228 migratory tracks collected from 102 adult breeding common terns (Sterna hirundo) aged 3-22 years, we find evidence that older terns navigate more efficiently than younger terns and that efficient navigation leads to a reduced migration duration and earlier arrival at the breeding and wintering grounds. We additionally find that the age-specificity of navigational efficiency in adult breeding birds cannot be explained by within-individual change with age (i.e. learning), suggesting the selective disappearance of less navigationally efficient individuals. This suggests that, at least in common terns, learning of navigational skills may be largely absent in adulthood, and limited to the pre-breeding phase of life where tracking is more difficult. We propose that selection might explain parts of the age-specificity of navigational performance observed in migratory taxa more generally; discuss the causes and evolutionary implications of variation in navigational traits and the selective agents acting upon them; and highlight the necessity of longitudinal studies when considering changes in behaviour with age.

Route flexibility is associated with headwind minimization in a long-distance migratory seabird

Seasonal migration has evolved across taxa and encompasses a multitude of features, many of which vary between species, between and within populations, and even within individuals. One feature of migration that appears especially variable within individuals is the route taken to reach a destination, even when the destination itself is not variable at this level. To investigate why, we analysed the geolocator tracks describing 192 post-breeding migratory journeys of 84 common terns (Sterna hirundo), as well as 149 pre-breeding migratory journeys of 75 of these birds. We found little within-individual spatial consistency in migration routes across years, irrespective of season or sex. Instead, individuals departing during the same time window took similar migration routes, which, during pre-breeding migration, when birds predominantly encountered headwinds, were associated with minimized headwind exposure. We therefore suggest that the individual routes of this long-distance migratory seabird can be flexibly adjusted to environmental variation, which is likely to be adaptive.

Origin stories: how does learned migratory behaviour arise in populations?

Although decades of research have deepened our understanding of the proximate triggers and ultimate drivers of migrations for a range of taxa, how populations establish migrations remains a mystery. However, recent studies have begun to illuminate the interplay between genetically inherited and learned migrations, opening the door to the evaluation of how migration may be learned, established, and maintained. Nevertheless, for migratory species where the role of learning is evident, we lack a comprehensive framework for understanding how populations learn specific routes and refine migratory movements over time (i.e., their origins). This review draws on advances in behavioural and movement ecology to offer a comprehensive framework for how populations could transition from resident to migratory by connecting cognitive research on fine-scale perceptual cues and movement decisions with literature on learning and cultural transmission, to the emergent pattern of migration. We synthesize the multiple cognitive mechanisms and processes that allow a population to respond to seasonal resource limitation, then encode spatial and environmental information about resource availability in memory and engage in social learning to navigate their landscapes and track resources better. A rise in global reintroduction efforts, along with human-induced rapid shifts in environmental cues and changing landscapes make evaluating the origins of this threatened behaviour more urgent than ever.

Social associations across species during nocturnal bird migration

An emerging frontier in ecology explores how organisms integrate social information into movement behavior and the extent to which information exchange occurs across species boundaries.1,2,3 Most migratory landbirds are thought to undertake nocturnal migratory flights independently, guided by endogenous programs and individual experience.4,5 Little research has addressed the potential for social information exchange aloft during nocturnal migration, but social influences that aid navigation, orientation, or survival could be valuable during high-risk migration periods.1,2,6,7,8 We captured audio of >18,000 h of nocturnal bird migration and used deep learning to extract >175,000 in-flight vocalizations of 27 species of North American landbirds.9,10,11,12 We used vocalizations to test whether migrating birds distribute non-randomly relative to other species in flight, accounting for migration phenology, geography, and other non-social factors. We found that migrants engaged in distinct associations with an average of 2.7 ± 1.9 SD other species. Social associations were stronger among species with similar wing morphologies and vocalizations. These results suggest that vocal signals maintain in-flight associations that are structured by flight speed and behavior.11,13,14 For small-bodied and short-lived bird species, transient social associations could play an important role in migratory decision-making by supplementing endogenous or experiential information sources.15,16,17 This research provides the first quantitative evidence of interspecific social associations during nocturnal bird migration, supporting recent calls to rethink songbird migration with a social lens.2 Substantial recent declines in bird populations18,19 may diminish the frequency and strength of social associations during migration, with currently unknown consequences for populations.

The spatial consistency and repeatability of migratory flight routes and stationary sites of individual European nightjars based on multiannual GPS tracks

BACKGROUND

The degree to which avian migrants revisit the same sites to replicate routes from previous years has received more and more attention as the possibilities of tracking small to medium-size birds over multiple annual cycles have improved. Repeated measurements of individuals with an appropriate sampling resolution can potentially inform about their navigation and migration strategies and to what extent observed variation within and between individuals may reflect the selective potential in the population.

METHODS

We analysed the annual space-use of European nightjars Caprimulgus europaeus tracked with GPS-loggers in multiple years between northern Europe and southern Africa. We quantified spatial consistency of stationary sites and variation, repeatability, and latitudinal correlations in route choice and also investigated barrier-associated changes of within- and between-individual longitudinal variation in flight routes.

RESULTS

We found that the nightjars consistently used the same breeding and wintering sites. In contrast, the birds generally varied their migration routes between years, and we could only rarely confirm site fidelity to stopover sites. Nevertheless, route variation within individuals remained low for most of both autumn and spring migration, while the between individual variation generally was larger, resulting in a high repeatability in flight routes. Although we found extensive spatial autocorrelation in both seasons across latitudes, we detected significant changes in longitudinal variation associated with the passage of ecological barriers enroute. Potential intermediate goal areas were visited prior to the crossing of the Mediterranean Sea and the Sahara Desert in both seasons. In spring, within-individual route variability dropped to a few tens of kilometres at the initiation of the Sahara crossing but increased to maximum over the barrier.

CONCLUSIONS

The nightjars incorporate individual-specific space use within their annual cycle that allows for a degree of flexibility during migration, possibly driven by the energetic benefits of allowing adaptive wind drift while airborne. Our data demonstrate how topography and spatial autocorrelation of positions influence flight path variability that may diminish or reinforce individuality in route choice. Hence, this study highlights that identifying and quantifying past and present external influences on emergence of realised routes can be critical for distinguishing the genetic basis and environmental variation in migration.

North American avian species that migrate in flocks show greater long-term non-breeding range shift rates

BACKGROUND

Many species are exhibiting range shifts associated with anthropogenic change. For migratory species, colonisation of new areas can require novel migratory programmes that facilitate navigation between independently-shifting seasonal ranges. Therefore, in some cases range-shifts may be limited by the capacity for novel migratory programmes to be transferred between generations, which can be genetically and socially mediated.

METHODS

Here we used 50 years of North American Breeding Bird Survey and Audubon Christmas Bird Count data to test the prediction that breeding and/or non-breeding range-shifts are more prevalent among flocking migrants, which possess a capacity for rapid social transmission of novel migration routes.

RESULTS

Across 122 North American bird species, social migration was a significant positive predictor for the magnitude of non-breeding centre of abundance (COA) shift within our study region (conterminous United States and Southern Canada). Across a subset of 81 species where age-structured flocking was determined, migrating in mixed-age flocks produced the greatest shifts and solo migrants the lowest. Flocking was not a significant predictor of breeding COA shifts, which were better explained by absolute population trends and migration distance.

CONCLUSIONS

Our results suggest that social grouping may play an important role in facilitating non-breeding distributional responses to climate change in migratory species. We highlight the need to gain a better understanding of migratory programme inheritance, and how this influences spatiotemporal population dynamics under environmental change.

Loss of Earth's old, wise, and large animals

Earth's old animals are in decline. Despite this, emerging research is revealing the vital contributions of older individuals to cultural transmission, population dynamics, and ecosystem processes and services. Often the largest and most experienced, old individuals are most valued by humans and make important contributions to reproduction, information acquisition and cultural transmission, trophic dynamics, and resistance and resilience to natural and anthropogenic disturbance. These observations contrast with the senescence-focused paradigm of old age that has dominated the literature for more than a century yet are consistent with findings from behavioral ecology and life history theory. In this work, we review why the global loss of old individuals can be particularly detrimental to long-lived animals with indeterminate growth; those with increasing reproductive output with age; and those dependent on migration, sociality, and cultural transmission for survival. Longevity conservation is needed to protect the important ecological roles and ecosystem services provided by old animals.

Tracking individual animals can reveal the mechanisms of species loss

As biodiversity loss continues, targeted conservation interventions are increasingly necessary. Stemming species loss requires mechanistic understanding of the processes governing population dynamics. However, this information is unavailable for most animals because it requires data that are difficult to collect using traditional methods. Advances in animal tracking technology have generated an avalanche of high-resolution observations for a growing list of species around the globe. To date, most research using these data has focused on questions about animal behavior, with less emphasis on population processes. Here, we argue that tracking data are uniquely poised to bring powerful new insights to the urgent, global problem of halting species extinctions by revealing when, where, how, and why populations are changing.

Mass Mortality in Terns and Gulls Associated with Highly Pathogenic Avian Influenza Viruses in Caspian Sea, Kazakhstan

Mass mortality in Caspian terns (Hydroprogne caspia), Pallas's gulls (Ichthyaetus ichthyaetus), and Caspian gulls (Larus cachinnans) was recorded on the northeastern shores of the Caspian Sea in June 2022. More than 5000 gulls and terns died due to the outbreak. The outbreak was investigated in the field, and representative numbers of samples were collected and analyzed using pathological, virological, and molecular methods. Highly pathogenic avian influenza A (H5N1) viruses were detected and isolated from samples collected from dead birds. Genetic and phylogenetic analyses indicated that the hemagglutinin (HA) genes belonged to the clade 2.3.4.4.b of the H5Nx HPAI viruses, B2 sub-lineage, and were closely related to the highly pathogenic influenza viruses, caused an outbreak in wild birds with a high mortality rate in the western part of the Caspian Sea.

Movement of juvenile migratory birds from settlement to adulthood across the non-breeding range

Among migratory vertebrates, high levels of fidelity to non-breeding sites during adulthood are common. If occupied sites vary in quality, strong site fidelity can have profound consequences for individual fitness and population demography. Given the prevalence of adult site fidelity, the regions of the non-breeding range to which juveniles first migrate, and the scale of any subsequent movements, are likely to be pivotal in shaping distributions and demographic processes across population ranges. However, inherent difficulties in tracking migratory individuals through early life mean that opportunities to quantify juvenile settlement and movements across non-breeding ranges, and the mechanisms involved, are extremely rare. Through long-term, range-wide resightings of hundreds of colour-marked individuals from their first migration to adulthood and the application of state-space models, we quantify levels of juvenile and adult regional-scale movements and distances at different life stages across the whole non-breeding distribution range in a migratory shorebird, the Black-tailed Godwit (Limosa limosa islandica). We show that the probability of individuals changing non-breeding regions (seven historical wintering regions spanning the Western Europe range) at all ages is very low (mean movement probability = 10.9% from first to subsequent winter, and 8.3% from first adult winter to later winters). Movement between regions was also low between autumn and winter of the same year for both juveniles (mean movement probability = 17.0%) and adults (10.4%). The great majority of non-breeding movements from the first autumn to adulthood were within regions and less than 100 km. The scarcity of regional-scale non-breeding movements from the first autumn to adulthood means that the factors influencing where juveniles settle will be key determinants of non-breeding distributions and of the rate and direction of changes in distributions.

The effects of cities on quail (Coturnix coturnix) migration: a disturbing story of population connectivity, health, and ecography

The increasing impact of human activities on ecosystems is provoking a profound and dangerous effect, particularly in wildlife. Examining the historical migration patterns of quail (Coturnix coturnix) offers a compelling case study to demonstrate the repercussions of human actions on biodiversity. Urbanization trends, where people gravitate toward mega-urban areas, amplify this effect. The proliferation of artificial urban ecosystems extends its influence across every biome, as human reliance on infrastructure and food sources alters ecological dynamics extensively. We examine European quail migrations pre- and post-World War II and in the present day. Our study concentrates on the Italian peninsula, investigating the historical and contemporary recovery of ringed quail populations. To comprehend changes in quail migration, we utilize trajectory analysis, open statistical data, and linear generalized models. We found that while human population and economic growth have shown a linear increase, quail recovery rates exhibit a U-shaped trajectory, and cereal and legume production displays an inverse U-shaped pattern. Generalized linear models have unveiled the significant influence of several key factors-time periods, cereal and legume production, and human demographics-on quail recovery rates. These factors closely correlate with the levels of urbanization observed across these timeframes. These insights underscore the profound impact of expanding human populations and the rise of mega-urbanization on ecosystem dynamics and services. As our planet becomes more urbanized, the pressure on ecosystems intensifies, highlighting the urgent need for concerted efforts directed toward conserving and revitalizing ecosystem integrity. Simultaneously, manage the needs and demands of burgeoning mega-urban areas. Achieving this balance is pivotal to ensuring sustainable coexistence between urban improvement and the preservation of our natural environment.

Global temperature homogenization can obliterate temporal isolation in migratory animals with potential loss of population structure

Climate change is expected to increase the spatial autocorrelation of temperature, resulting in greater synchronization of climate variables worldwide. Possibly such 'homogenization of the world' leads to elevated risks of extinction and loss of biodiversity. In this study, we develop an empirical example on how increasing synchrony of global temperatures can affect population structure in migratory animals. We studied two subspecies of bar-tailed godwits Limosa lapponica breeding in tundra regions in Siberia: yamalensis in the west and taymyrensis further east and north. These subspecies share pre- and post-breeding stopover areas, thus being partially sympatric, but exhibiting temporal segregation. The latter is believed to facilitate reproductive isolation. Using satellite tracking data, we show that migration timing of both subspecies is correlated with the date of snowmelt in their respective breeding sites (later at the taymyrensis breeding range). Snow-cover satellite images demonstrate that the breeding ranges are on different climate trajectories and become more synchronized over time: between 1997 and 2020, the date of snowmelt advanced on average by 0.5 days/year in the taymyrensis breeding range, while it remained stable in the yamalensis breeding range. Previous findings showed how taymyrensis responded to earlier snowmelt by advancing arrival and clutch initiation. In the predicted absence of such advancements in yamalensis, we expect that the two populations will be synchronized by 2036-2040. Since bar-tailed godwits are social migrants, this raises the possibility of population exchange and prompts the question whether the two subspecies can maintain their geographic and morphological differences and population-specific migratory routines. The proposed scenario may apply to a wide range of (social) migrants as temporal segregation is crucial for promoting and maintaining reproductive isolation in many (partially sympatric) migratory populations. Homogenization of previously isolated populations could be an important consequence of increasing synchronized environments and hence climate change.

Dispersal of juvenile Barrow's goldeneyes (Bucephala islandica) mirrors that of breeding adults

Barrow's goldeneyes across western North America have been shown to have a high degree of subpopulation independence using several data types. However, evidence for structured populations based on mitochondrial DNA, band recoveries, and tracking of adults is discordant with evidence from autosomal DNA. We used satellite tracking data from both juveniles and adults marked on natal and breeding grounds, respectively, in British Columbia, Canada to evaluate the hypothesis that male-biased juvenile dispersal maintains genetic panmixia of Pacific Barrow's goldeneyes otherwise structured by migratory movements and high winter and breeding site fidelity of adults. We found that juvenile males traveled to overwintering sites located within the range of the overwintering sites of juvenile females, adult males, and adult females. Juvenile males migrated at the same time, travelled the same distance when moving between natal and overwintering sites, and had the same winter dispersion as juvenile females. Although juveniles did not travel with attendant females, all juveniles overwintered within the wintering range of adults. We tracked some juveniles into the following spring/summer and even second winter. Prospecting juveniles of both sexes travelled from their wintering grounds to potential breeding sites in the proximity of Riske Creek and within the bounds of the breeding locations used by adults. Juveniles tracked for more than a year also showed relatively high winter site fidelity. Because Barrow's goldeneyes pair on wintering grounds, our tracking data are not consistent with the hypothesis that male-biased juvenile dispersal explains the genetic structure in the mitochondrial DNA and panmixia in the autosomal DNA of Barrow's goldeneye. We suggest that uncommon or episodic dispersal of males might be enough to homogenize autosomal DNA but is unlikely to influence demographic population structure relevant to contemporary population management.

Weather, sex and body condition affect post-fledging migration behaviour of the greater flamingo Phoenicopterus roseus

BACKGROUND

Understanding which intrinsic and extrinsic factors dictate decision-making processes such as leaving the natal area or not (migratory vs resident strategy), departure time, and non-breeding destination are key-issues in movement ecology. This is particularly relevant for a partially migratory meta-population in which only some individuals migrate.

METHODS

We investigated these decision making-processes for 40 juvenile greater flamingos Phoenicopterus roseus fledged in three Mediterranean colonies and equipped with GPS-GSM devices.

RESULTS

Contrary to the body size and the dominance hypotheses, juveniles in better body condition were more likely to migrate than those in worse conditions, which opted for a residence strategy. Flamingo probability of departure was not associated with an increase in local wind intensity, but rather with the presence of tailwinds with departure limited to night-time mostly when the wind direction aligned with the migratory destination. Moreover, a positive interaction between tailwind speed and migration distance suggested that juveniles opted for stronger winds when initiating long-distance journeys. In contrast to previous studies, the prevailing seasonal winds were only partially aligned with the migratory destination, suggesting that other factors (e.g., adults experience in mix-aged flocks, availability of suitable foraging areas en route, density-dependence processes) may be responsible for the distribution observed at the end of the first migratory movement. We found potential evidence of sex-biased timing of migration with females departing on average 10 days later and flying ca. 10 km/h faster than males. Female flight speed, but not male one, was positively influenced by tailwinds, a pattern most likely explained by sexual differences in mechanical power requirements for flight (males being ca. 20% larger than females). Furthermore, juveniles considerably reduced their flight speeds after 400 km from departure, highlighting a physiological threshold, potentially linked to mortality risks when performing long-distance non-stop movements.

CONCLUSION

These results suggest that not only intrinsic factors such as individual conditions and sex, but also extrinsic factors like weather, play critical roles in triggering migratory behaviour in a partially migratory metapopulation. Furthermore, social factors, including conspecific experience, should be taken into consideration when evaluating the adaptive processes underlying migration phenology, flight performance, and final destination selection.

The price of being late: short- and long-term consequences of a delayed migration timing

Choosing the right migration timing is critical for migrants because conditions encountered en route influence movement costs, survival, and, in social migrants, the availability of social information. Depending on lifetime stages, individuals may migrate at different times due to diverging constraints, affecting the composition of migration groups. To examine the consequences of a delayed migration timing, we artificially delayed the migration of juvenile white storks (Ciconia ciconia) and thereby altered their physical and social environment. Using nearly continuous 1 Hz GPS trajectories, we examined their migration behaviour, ranging from sub-second level performance to global long-distance movement, in relation to two control groups. We found that delayed storks experienced suboptimal soaring conditions, but better wind support and thereby achieved higher flight speeds than control storks. Delayed storks had a lower mortality rate than the control storks and wintered closer to the breeding area. In fact, none of the delayed storks reached the traditional African wintering areas. Thus, our results show that juvenile storks can survive migrating at the 'wrong' time. However, this had long-term consequences on migration decisions. We suggest that, when timing their migration, storks balance not just energy and time, but also the availability of social information.

The Yellow-browed Warbler (Phylloscopus inornatus) as a model to understand vagrancy and its potential for the evolution of new migration routes

Why and how new migration routes emerge remain fundamental questions in ecology, particularly in the context of current global changes. In its early stages, when few individuals are involved, the evolution of new migration routes can be easily confused with vagrancy, i.e. the occurrence of individuals outside their regular breeding, non-breeding or migratory distribution ranges. Yet, vagrancy can in theory generate new migration routes if vagrants survive, return to their breeding grounds and transfer their new migration route to their offspring, thus increasing a new migratory phenotype in the population. Here, we review the conceptual framework and empirical challenges of distinguishing regular migration from vagrancy in small obligate migratory passerines and explain how this can inform our understanding of migration evolution. For this purpose, we use the Yellow-browed Warbler (Phylloscopus inornatus) as a case study. This Siberian species normally winters in southern Asia and its recent increase in occurrence in Western Europe has become a prominent evolutionary puzzle. We first review and discuss available evidence suggesting that the species is still mostly a vagrant in Western Europe but might be establishing a new migration route initiated by vagrants. We then list possible empirical approaches to check if some individuals really undertake regular migratory movements between Western Europe and Siberia, which would make this species an ideal model for studying the links between vagrancy and the emergence of new migratory routes.

Decadal migration phenology of a long-lived Arctic icon keeps pace with climate change

Animals migrate in response to seasonal environments, to reproduce, to benefit from resource pulses, or to avoid fluctuating hazards. Although climate change is predicted to modify migration, only a few studies to date have demonstrated phenological shifts in marine mammals. In the Arctic, marine mammals are considered among the most sensitive to ongoing climate change due to their narrow habitat preferences and long life spans. Longevity may prove an obstacle for species to evolutionarily respond. For species that exhibit high site fidelity and strong associations with migration routes, adjusting the timing of migration is one of the few recourses available to respond to a changing climate. Here, we demonstrate evidence of significant delays in the timing of narwhal autumn migrations with satellite tracking data spanning 21 y from the Canadian Arctic. Measures of migration phenology varied annually and were explained by sex and climate drivers associated with ice conditions, suggesting that narwhals are adopting strategic migration tactics. Male narwhals were found to lead the migration out of the summering areas, while females, potentially with dependent young, departed later. Narwhals are remaining longer in their summer areas at a rate of 10 d per decade, a similar rate to that observed for climate-driven sea ice loss across the region. The consequences of altered space use and timing have yet to be evaluated but will expose individuals to increasing natural changes and anthropogenic activities on the summering areas.

Viewing animal migration through a social lens

Evidence of social learning is growing across the animal kingdom. Researchers have long hypothesized that social interactions play a key role in many animal migrations, but strong empirical support is scarce except in a few unique systems and species. In this review, we aim to catalyze advances in the study of social migrations by synthesizing research across disciplines and providing a framework for understanding when, how, and why social influences shape the decisions animals make during migration. Integrating research across the fields of social learning and migration ecology will advance our understanding of the complex behavioral phenomena of animal migration and help to inform conservation of animal migrations in a changing world.

Paternal transmission of migration knowledge in a long-distance bird migrant

While advances in biologging have revealed many spectacular animal migrations, it remains poorly understood how young animals learn to migrate. Even in social species, it is unclear how migratory skills are transmitted from one generation to another and what implications this may have. Here we show that in Caspian terns Hydroprogne caspia family groups, genetic and foster male parents carry the main responsibility for migrating with young. During migration, young birds stayed close to an adult at all times, with the bond dissipating on the wintering grounds. Solo-migrating adults migrated faster than did adults accompanying young. Four young that lost contact with their parent at an early stage of migration all died. During their first solo migration, subadult terns remained faithful to routes they took with their parents as young. Our results provide evidence for cultural inheritance of migration knowledge in a long-distance bird migrant and show that sex-biased (allo)parental care en route shapes migration through social learning.