Steffen Hahn

Swiss Ornithological Institute · Bird Migration

Migratory connectivity can have important consequences for individuals, populations and communities. We argue that most consequences not only depend on which sites are used but importantly also on when these are used and suggest that the timing of migration is characterised by synchrony, phenology, and consistency. We illustrate the importance of t...

In migratory birds, morphological adaptations for efficient migratory flight often oppose morphological adaptations for efficient behavior during resident periods. This includes adaptations in wing shape for either flying long distances or foraging in the vegetation and in climate-driven variation of body size. In addition, the timing of migratory...

Over decades it has been unclear how individual migratory songbirds cross large ecological barriers such as seas or deserts. By deploying light-level geolocators on four songbird species weighing only about 12 g, we found that these otherwise mainly nocturnal migrants seem to regularly extend their nocturnal flights into the day when crossing the S...

Blood parasites (Haemosporidia) are thought to impair the flight performance of infected animals, and therefore, infected birds are expected to differ from their non-infected counterparts in migratory capacity. Since haemosporidians invade host erythrocytes, it is commonly assumed that infected individuals will have compromised aerobic capacity, bu...

It is well established that the nutrient and energy requirements of birds increase substantially during moult, but it is not known if these increased demands affect their aerobic capacity. We quantified the absolute aerobic scope of house and Spanish sparrows, Passer domesticus and P. hispaniolensis, respectively, before and during sequential stage...

Understanding how weather conditions affect animal populations is essential to foresee population changes in times of global climate shifts. However, assessing year-round weather impacts on demographic parameters is hampered in migratory animals due to often unknown occurrence in space and time. We addressed this by coupling tracking and weather da...

Using EURING data and geolocation, we describe migration routes and the nonbreeding range of Red-rumped Swallows breeding in the Western Palearctic. One bird ringed in southern Spain and recovered in southern Morocco indicates southwestern migration; geolocator data from five birds from central and eastern Iberian Peninsula confirm migration to var...

Background Migratory birds differ markedly in their migration strategies, particularly those performing short- versus long-distance migrations. In preparation for migration, all birds undergo physiological and morphological modifications including enlargement of fat stores and pectoral muscles to fuel and power their flights, as well as cardiovascu...

East Asian songbirds are known to migrate along two major corridors: from mainland Eurasia via China to SouthEast Asia, and from Japan and easternmost Russia through chains of islands in the Pacific to Indonesia and the Philippines. We successfully tracked the hitherto unknown migration of a Blue-and-white Flycatcher Cyanoptila cyanomelana breeding...

Understanding the relationship between migratory performance and fitness is crucial for predicting population dynamics of migratory species. In this study, we used geolocators to explore migration performance (speed and duration of migratory movements, migratory timings) and its association with breeding phenology and productivity in an Afro-Palear...

The black-headed bunting is one of the few species that migrate along the Indo-European flyway, and its migration routes and phenology are poorly understood. We provide the first individual-based year-round tracking study describing route choice and timing of black-headed buntings migrating from a breeding site in Croatia to a 6000 km distant non-b...

Background Populations of long-distance migratory birds experience different environments and are consequently exposed to different parasites throughout their annual cycles. Though, specific whereabouts and accompanied host-parasite interactions remain unknown for most migratory passerines. Collared sand martins (Riparia riparia) breeding in the we...

Annual cycle events may be interlinked, influence following annual cycle stages, and may alter performance of individuals. Such links, called carry-over effects, can explain individual variation in timing or reproductive success in migratory species. Identifying the key links affecting fitness may reveal the mechanisms of species population dynamic...

How blood parasite infections influence the migration of hosts remains a lively debated issue as past studies found negative, positive, or no response to infections. This particularly applies to small birds, for which monitoring of detailed migration behavior over a whole annual cycle has been technically unachievable so far. Here, we investigate h...

In water rails Rallus aquaticus, northern and eastern populations are migratory while southern and western populations are sedentary. Few details are known about the annual cycle of this elusive species. We studied movements and breeding in water rails from southernmost Norway where the species occurs year‐round. Colour‐ringed wintering birds occur...

Data from remote sensing are often used as proxies to quantify biological processes, especially at large geographical scales. The normalized difference vegetation index (NDVI) is the most frequently used proxy for primary productivity. Assuming a direct, positive interrelation between primary and secondary production in terrestrial habitats, NDVI i...

Amongst other factors, host behaviour critically determines the patterns with which blood parasites occur in wild host populations. In particular, migratory hosts that sequentially occupy distant sites within and across years are expected to show distinct patterns of blood parasitism depending on their population-specific schedules and whereabouts....

Migratory birds complete their seasonal journeys between breeding and non‐breeding sites with a series of migratory flights that are separated by prolonged stopovers. While songbirds are the most common taxa among migratory birds, empirical data on flight and stopover behaviour along their entire migratory journeys are still rare. Here, we integrat...

Capsule: A combination of several biometric measures enables the reliable sexing of the European Bee-eater Merops apiaster, a species with subtle sex differences in plumage and morphometry. Aims: To explore variation in biometrics and their suitability to discriminate sex in adult European Bee-eaters Merops apiaster. Methods: We sampled populations...

Aim: Knowledge of broad-scale biogeographical patterns of animal migration is important for understanding ecological drivers of migratory behaviours. Here, we present a flyway-scale assessment of the spatial structure and seasonal dynamics of the Afro-Palaearctic bird migration system and explore how phenology of the environment guides long-distanc...

Currently, the deployment of tracking devices is one of the most frequently used approaches to study movement ecology of birds. Recent miniaturisation of light‐level geolocators enabled studying small bird species whose migratory patterns were widely unknown. However, geolocators may reduce vital rates in tagged birds and may bias obtained movement...

Across their ranges, different populations of migratory species often use separate routes to migrate between breeding and non‐breeding grounds. Recent changes in climate and land‐use have led to breeding range expansions in many species, but it is unclear whether these populations also establish new migratory routes, non‐breeding sites and migratio...

In many taxa, the most common form of sex-biased migration timing is protandry-the earlier arrival of males at breeding areas. Here we test this concept across the annual cycle of long-distance migratory birds. Using more than 350 migration tracks of small-bodied trans-Saharan migrants, we quantify differences in male and female migration schedules...

Birds that are long-distance migrants partition their annual cycle among a number of locations over a large spatial range. The conservation of these species is particularly complex because it requires attention to a number of different and distant habitats based on knowledge of migratory phenology, routes and staging areas. In the case of the globa...

Mobile hosts like birds occupy a wide array of habitats in which they encounter various vector and parasite faunas. If the infection probability for vector-borne parasites varies among seasons and biomes, a migratory life can critically influence the infections of a host. The growing body of literature on avian blood parasites suggests that host mi...

Background Over the past decade, the miniaturisation of animal borne tags such as geolocators and GPS-transmitters has revolutionized our knowledge of the whereabouts of migratory species. Novel light-weight multi-sensor loggers (1.4 g), which harbour sensors for measuring ambient light intensity, atmospheric pressure, temperature and acceleration,...

On the Balkan Peninsula, migratory Spanish Sparrows breed sympatrically with resident House Sparrows. While the two species share many biological and ecological traits, migratory patterns and adaptions to migratory lifestyle of the Spanish Sparrow are unknown. We tracked a Spanish Sparrow across its 1800 km long migration from Bulgaria to the nonbr...

Knowledge on whereabouts within the annual cycle of migratory species is prerequisite for many aspects in ecology and biological conservation. Spatial assignments of stable isotopes archived in tissues allows for later inference on sites where the specific tissue had been grown. It has been rarely tested whether spatial assignments match directly t...

Predicted moult origin/overwintering regions for two individual barn swallows based on isotope assignment for three isotopes δ2H, δ13C and δ15N and geolocation. 75% Kernel density estimates are shown in red. a) Example of best geographical overlap. b) Example of least overlap. (TIFF)

Thousands of species migrate [1]. Though we have some understanding of where and when they travel, we still have very little insight into who migrates with whom and for how long. Group formation is pivotal in allowing individuals to interact, transfer information, and adapt to changing conditions [2]. Yet it is remarkably difficult to infer group m...

The annual cycle of migrating birds is shaped by their seasonal movements between breeding and non-breeding sites. Studying how migratory populations are linked throughout the annual cycle—migratory connectivity, is crucial to understanding the population dynamics of migrating bird species. This requires the consideration not only of spatial scales...

Under time‐selected migration, birds should choose a strategy for outcompeting rivals over securing access to prime resources at the final destination. Thus, migration can be viewed as a race among individuals where winners are arriving first when conditions are suitable. The sprint migration hypothesis predicts that individuals shift from maximum...

Whether long‐distance animal migration facilitates or hampers pathogen transmission depends on how infections affect the routes and timing of migrating hosts. If an infection directly or indirectly impedes migratory flight capacity, infected individuals lag behind their uninfected conspecifics. Although such temporal segregation can limit parasite...

Seasonal variation in migratory routes seems to be a common trait among many Afro-Palearctic migrants, but there are only few examples of species or populations which shift between entirely different flyways in autumn and spring. To identify non-breeding regions and seasonal differences in migration strategies we tracked Barn Swallows (Hirundo rust...

In their 2015 Current Biology paper, Streby et al. [1] reported that Golden-winged Warblers (Vermivora chrysoptera), which had just migrated to their breeding location in eastern Tennessee, performed a facultative and up to “>1,500 km roundtrip” to the Gulf of Mexico to avoid a severe tornadic storm. From light-level geolocator data, wherein geogra...

Migratory birds often move significantly within their nonbreeding range before returning to breed. It remains unresolved under which circumstances individuals relocate, whether movement patterns are consistent between populations and to which degree the individuals benefit from the intratropical movement (ITM). We tracked adult great reed warblers...

Nonbreeding sites of the tracked great reed warblers with the quartiles in longitude and latitude

The Blackcap Sylvia atricapilla is a model species for the evolution of bird migration in a time of global change. However, many assumptions about putative changes to their migratory paths have not been verified because, until recently, it has not been possible to track individual small passerines throughout the entire migration cycle. With the rec...

Background: Adjusting the timing of annual events to gradual changes in environmental conditions is necessary for population viability. However, adaptations to weather extremes are poorly documented in migratory species. Due to their vast seasonal movements, long-distance migrants face unique challenges in responding to changes as they rely on an e...

Animals which spend subsequent seasons in different areas connect geographical regions. The connection between breeding and non-breeding grounds is defined as migratory connectivity. The quantification of such connectivity is important, because movements between different locations can have strong consequences for the moving animal as well as the e...

Seabirds show remarkable variability in migration strategies among individuals and populations. In this study we analysed 47 migrations of 28 brown skuas Catharacta antarctica lonnbergi breeding on King George Island in the Maritime Antarctic. Brown skuas from this population used a large area during the non-breeding period north of 55°S, including...

Aim Assessing the extent of large-scale migratory connectivity is crucial for understanding the evolution of migratory systems and effective species conservation. It has been, however, difficult to elucidate the annual whereabouts of migratory populations of small animals across the annual cycle. Here, we use the reed warbler (Acrocephalus scirpac...

Many Arctic-breeding waterbirds are thought to bring nutrients for egg production from southern latitudes to allow early breeding. It has proved problematic to quantify the extent of such capital breeding and identify whether nutrients for egg production are brought in from nearby or from afar. Before reaching their breeding grounds on Svalbard, pi...

The central-eastern European populations of sand martin and house martin have declined in the last decades. The drivers for this decline cannot be identified as long as the whereabouts of these long distance migrants remain unknown outside the breeding season. Ringing recoveries of sand martins from central-eastern Europe are widely scattered in th...

How individual birds schedule their movements and use different sites during the non-breeding season are fundamental issues in avian migration ecology, and studies have often revealed strong seasonal variation in such strategies. Using geolocators we tracked Common Ringed Plovers Charadrius hiaticula from northern Norway to West Africa and back to...

Studying parasitism in migrating animals is difficult, as breeding grounds – the only location where such studies can take place – are only inhabited for few weeks or months. Thus, already the choice of a suitable study species proves to be a difficult task. Despite these difficulties, migrant hosts are interesting to study: They are assumed to be...

Long-term shifts in vegetation phenology generally follow the pattern of global warming. Yet, topographical complexity and biome diversity cause uneven spatial trends in the phenological response of vegetation to climate change. If phenology changes similarly along migration routes, individuals may adequately respond by shifting the whole migration...

Timing the annual cycle according to local conditions is crucial for animals in seasonal environments, because individual resource requirements must match seasonal resource availabilities. Pre-nuptial spring migration is especially time constrained in many migratory species, and thus tight adjustments of departure and arrival times to local environ...

The temporal and spatial organization of the annual cycle according to local conditions is of crucial importance for individuals’ fitness. Moreover, which sites and when particular sites are used can have profound consequences especially for migratory animals, because the two factors shape interactions within and between populations, as well as bet...

We examined migration routes and nonbreeding sites of a poorly studied long-distance migrant, the Semi-collared Flycatcher Ficedula semitorquata, by tracking adult birds with geolocators from an eastern European breeding population across two subsequent years. All 11 birds migrated in a clockwise loop fashion where autumn migration routes lay east...