Ecological conditions in wintering and passage areas as determinants of timing of spring migration in trans-Saharan migratory birds

1.?Climate change has been associated with shifts in the timing of biological events, including the spring arrival of migratory birds. Early arrival at breeding sites is an important life-history trait, usually associated with higher breeding success and therefore, susceptible to selection and evolution in response to changing climatic conditions. 2.?Here, we examine the effect of changes in the environmental conditions of wintering and passage areas on the mean passage time of 13 trans-Saharan passerines during their spring migration through the western Mediterranean over the 15 years from 1993 to 2007. 3.?We found that most of the species studied have been advancing the timing of their passage in recent years. However, annual variation in the mean date of passage was positively correlated with vegetation growth (measured as the normalized difference vegetation index [NDVI]) both in the Sahel (the region of departure) and in northern Africa (the passage area). Thus, migration dates were delayed in years with high primary productivity in passage and wintering zones. All species seem to respond similarly to NDVI in the Sahel; however, late migrants were less affected by ecological conditions in northern Africa than those migrating earlier, suggesting differences based on species ecology. 4.?Mean timing of passage was not related to the North Atlantic Oscillation (NAO), El Ni?o-Southern Oscillation (ENSO), temperature or NDVI in the species-specific wintering areas (the overwintering region) when analysed in combination with the other covariates. 5.?Our findings show that ecological conditions in the winter quarters (specifically the Sahel) and en route are relevant factors influencing trends in the passage dates of trans-Saharan migratory birds on the southern fringe of Europe. Possible long-term consequences for late arriving spring migrants are discussed.     

Local temperature fine-tunes the timing of spring migration in birds

Evidence for climate-driven phenological changes is rapidly increasing at all trophic levels. Our current poor knowledge of the detailed control of bird migration from the level of genes and hormonal control to direct physiological and behavioral responses hampers our ability to understand and predict consequences of climatic change for migratory birds. In order to better understand migration phenology and adaptation in environmental changes, we here assess the scale at which weather affects timing of spring migration in passerine birds. We use three commonly used proxies of spring-time climatic conditions: (1) vegetation "greenness" (NDVI) in Europe, (2) local spring temperatures in northern Europe, and (3) the North Atlantic Oscillation Index (NAO) as predictors of the phenology of avian migration as well as the strength of their effect on different subsets of populations and the dependence of correlations on species-specific migratory strategy. We analyze phenological patterns of the entire spring migration period in 12 Palaearctic passerine species, drawing on long-term data collected at three locations along a longitudinal gradient situated close to their northern European breeding area. Local temperature was the best single predictor of phenology with the highest explanatory power achieved in combination with NAO. Furthermore, early individuals are more affected by climatic variation compared to individuals on later passage, indicating that climatic change affects subsets of migratory populations differentially. Species wintering closer to the breeding areas were affected more than were those travelling longer distances and this pattern was strongest for the earliest subsets of the population. Overall, our results suggest that at least early subsets of the population are affected by local conditions and early birds use local conditions to fine-tune the date of their spring arrival while individuals arriving later are driven by other factors than local conditions e.g. endogenous control. Understanding what cues migratory organisms use to arrive at an optimum time is important for increasing our knowledge of fundamental issues like decision making in organisms during migration and is crucial for future protection of migratory organisms.     

Climatic connectivity between Africa and Europe may serve as a basis for phenotypic adjustment of migration schedules of trans-Saharan migratory birds

Most European migratory birds wintering in sub‐Saharan Africa have anticipated arrival to the breeding areas over the past decades. This phenological change may be ultimately caused by warming of the Northern Hemisphere via evolutionary changes or phenotypic plasticity in migration behavior. First arrival dates are negatively predicted by temperatures upon arrival to the breeding grounds. This seems puzzling, because migrants should be unable to predict weather conditions at long range. Migrants can enjoy diverse fitness benefits from early arriving. However, if weather conditions at destination cannot be predicted, early arrival can also entail severe costs. If meteorological conditions in Europe during breeding covary with those in sub‐Saharan Africa during late winter, long‐distance migrants may have a clue to predict meteorological conditions in their breeding areas while they are still in Africa and adjust their migration schedule consequently, an idea that has never been tested. We analyzed the correlation between March–April temperature anomalies (T_an) in Europe and February T_an in the Sahel and sub‐Sahel, where long‐distance migrants winter or stop‐over. T_an in Africa negatively predicted T_an in Europe, the association being particularly strong (unsigned effect size, z_r>0.35) for eastern Sahel and northern and eastern Europe, where the risks of early arrival may be larger. However, the strength of the correlations between T_an in the two continents has declined during the last 25 years; thus, possibly, partly compromising adaptive mechanisms of adjustment of migration. The existence of such climatic connectivity leads to several predictions, including that positive T_an in Africa should delay arrival. Consistent with this prediction, we found that first arrival dates of seven long‐distance migratory species positively covaried with February T_an in Africa. Thus, while wintering, migrants might be able to predict meteorological conditions at the beginning of the breeding season, and phenotypically adjust migration schedules to optimally tune arrival date.     

Spring arrival along a migratory divide of sympatric blackcaps (Sylvia atricapilla)

The recent formation of a migratory divide in the blackcap (Sylvia atricapilla) involves sympatrically breeding birds migrating to different overwintering quarters. Within the last 50 years, a novel migratory strategy has evolved resulting in an increasing proportion of birds now wintering in Britain instead of migrating to the traditional sites in the Mediterranean area. This rapid microevolution has been attributed to allochronic spring arrival of migrants from the respective wintering quarters leading to assortative mating. Moreover, blackcaps wintering in Britain may experience fitness advantages owing to improved local wintering conditions. We used stable hydrogen isotope signatures (δD) to scrutinize the degree of temporal segregation of blackcaps upon spring arrival and to test for carry-over effects in body condition associated with the disparate wintering environments. Although we found that migrants from Britain arrive significantly earlier on German breeding grounds than migrants from the Mediterranean region, we also found a considerable overlap in arrival times. In a resampling model, the mean probability of assortative mating of birds wintering in Britain is ≤28% in both years. These results suggest that allochrony alone is not a strong isolating barrier between the two subpopulations. Migrants from both wintering locations did not differ in terms of body mass, mass-tarsus residuals or mass-tarsus ratio and arrived in a similar reproductive disposition. Thus, blackcaps wintering in Britain do not gain an apparent fitness advantage on spring migration due to carry-over effects in body condition. Future studies should explore additional factors such as differences in song quality and habitat that might contribute to the rapid microevolution of the blackcap.     

Advanced departure dates in long-distance migratory raptors

Evidences for phenological changes in response to climate change are now numerous. One of the most documented changes has been the advance of spring arrival dates in migratory birds. However, the effects of climate change on subsequent events of the annual cycle remain poorly studied and understood. Moreover, the rare studies on autumn migration have mainly concerned passerines. Here, we investigated whether raptor species have changed their autumn migratory phenology during the past 30 years at one of the most important convergent points of western European migration routes in France, the Organbidexka pass, in the Western Pyrenees. Eight out of the 14 studied raptor species showed significant phenological shifts during 1981–2008. Long-distance migrants displayed stronger phenological responses than short-distance migrants, and advanced their mean passage dates significantly. As only some short-distance migrants were found to delay their autumn migration and as their trends in breeding and migrating numbers were not significantly negative, we were not able to show any possible settling process of raptor populations. Negative trends in numbers of migrating raptors were found to be related to weaker phenological responses. Further studies using data from other migration sites are necessary to investigate eventual changes in migration routes and possible settling process.     

Photoperiodic response may facilitate adaptation to climatic change in long-distance migratory birds

Recent climatic change is causing spring events in northern temperate regions to occur earlier in the year. As a result, migratory birds returning from tropical wintering sites may arrive too late to take full advantage of the food resources on their breeding grounds. Under these conditions, selection will favour earlier spring arrival that could be achieved by overwintering closer to the breeding grounds. However, it is unknown how daylength conditions at higher latitudes will affect the timing of life cycle stages. Here, we show in three species of Palaearctic-African migratory songbirds that a shortening of migration distance induces an advancement of springtime activities. Birds exposed to daylengths simulating migration to and wintering in southern Europe considerably advanced their spring migratory activity and testicular development. This response to the novel photoperiodic environment will enable birds wintering further north to advance spring arrival and to start breeding earlier. Thus, phenotypic flexibility in response to the photoperiod may reinforce selection for shorter migration distance if spring temperatures continue to rise.     

Migratory diversity predicts population declines in birds

Declines in migratory species are a pressing concern worldwide, but the mechanisms underpinning these declines are not fully understood. We hypothesised that species with greater within‐population variability in migratory movements and destinations, here termed ‘migratory diversity’, might be more resilient to environmental change. To test this, we related map‐based metrics of migratory diversity to recent population trends for 340 European breeding birds. Species that occupy larger non‐breeding ranges relative to breeding, a characteristic we term ‘migratory dispersion’, were less likely to be declining than those with more restricted non‐breeding ranges. Species with partial migration strategies (i.e. overlapping breeding and non‐breeding ranges) were also less likely to be declining than full migrants or full residents, an effect that was independent of migration distance. Recent rates of advancement in Europe‐wide spring arrival date were greater for partial migrants than full migrants, suggesting that migratory diversity may also help facilitate species responses to climate change.     

Climatic responses in spring migration of boreal and arctic birds in relation to wintering area and taxonomy

Large‐scale climate fluctuations, such as the North Atlantic Oscillation (NAO), have a marked effect on the timing of spring migration of birds. It has however been suggested that long‐distance migrants wintering in Africa could respond less to NAO than short‐distance migrants wintering in Europe, making them more vulnerable to climatic changes. We studied whether migratory boreal and arctic bird species returning from different wintering areas show differences in responses to the NAO in the timing of their spring migration. We used data on 75 species from two bird observatories in northern Europe (60°N). By extending the examination to the whole distribution of spring migration and to a taxonomically diverse set of birds, we aimed at finding general patterns of the effects of climate fluctuation on the timing of avian migration. Most species arrived earlier after winters with high NAO index. The degree of NAO‐response diminished with the phase of migration: the early part of a species’ migratory population responded more strongly than the later part. Early phase waterfowl responded strongest to NAO, but in later phases their response faded to non‐significant. This pattern may be related to winter severity and/or ice conditions in the Baltic. In the two other groups, gulls and waders and passerines, all phases of migration responded to NAO and fading with phase was non‐significant. The difference between waterfowl and other groups may be related to differences between the phenological development of their respective macrohabitats. Wintering area affected the strength of NAO response in a complicated way. On average medium distance migrants responded most strongly, followed by short‐distance migrants and partial migrants. Our results concerning the response of long‐distance migrants were difficult to interpret: there is an overall weak yet statistically significant effect, but patterns with phase of migration need further study. Our results highlight the importance of examining the whole distribution of migration and warrant the use of data sets from several sampling sites when studying climatic effects on the timing of avian life‐history events.     

Contrasting Patterns of Genetic Differentiation among Blackcaps (Sylvia atricapilla) with Divergent Migratory Orientations in Europe

Migratory divides are thought to facilitate behavioral, ecological, and genetic divergence among populations with different migratory routes. However, it is currently contentious how much genetic divergence is needed to maintain distinct migratory behavior across migratory divides. Here we investigate patterns of neutral genetic differentiation among Blackcap (Sylvia atricapilla) populations with different migratory strategies across Europe. We compare the level of genetic divergence of populations migrating to southwestern (SW) or southeastern (SE) wintering areas with birds wintering in the British Isles following a recently established northwesterly (NW) migration route. The migratory divide between SW and SE wintering areas can be interpreted as a result of a re-colonization process after the last glaciation. Thus we predicted greater levels of genetic differentiation among the SW/SE populations. However, a lack of genetic differentiation was found between SW and SE populations, suggesting that interbreeding likely occurs among Blackcaps with different migratory orientations across a large area; therefore the SW/SE migratory divide can be seen as diffuse, broad band and is, at best, a weak isolating barrier. Conversely, weak, albeit significant genetic differentiation was evident between NW and SW migrants breeding sympatrically in southern Germany, suggesting a stronger isolating mechanism may be acting in this population. Populations located within/near the SW/SE contact zone were the least genetically divergent from NW migrants, confirming NW migrants likely originated from within the contact zone. Significant isolation-by-distance was found among eastern Blackcap populations (i.e. SE migrants), but not among western populations (i.e. NW and SW migrants), revealing different patterns of genetic divergence among Blackcap populations in Europe. We discuss possible explanations for the genetic structure of European Blackcaps and how gene flow influences the persistence of divergent migratory behaviors.     

Climatic effects on timing of spring migration and breeding in a long-distance migrant, the pied flycatcher Ficedula hypoleuca

Climate change has advanced the breeding dates of many bird species, but for few species we know whether this advancement is sufficient to track the advancement of the underlying levels of the food chain. For the long-distance migratory pied flycatcher Ficedula hypoleuca the advancement in breeding time has been insufficient to maintain the synchrony with their main food sources. The timing of arrival in the breeding areas from their African wintering grounds is likely to constrain the advancement of breeding date. We hypothesise that this is because in Africa they cannot predict the advancement of spring in their breeding habitat. However, long-distance migrants may advance their arrival time by migrating faster when circumstances en route are favourable. In this study we show that both arrival and breeding date depend on temperatures at their main North African staging grounds, as well as on temperature at the breeding grounds. Male arrival and average laying date were not correlated, but the positive effect of temperature in North Africa on breeding dates suggests that breeding date is indeed constrained by arrival of females. Long-distance migrants thus are able to adjust arrival and hence breeding by faster spring migration, but the degree of adjustment is probably limited as timing schedules in spring are tight. Furthermore, as climate change is affecting temperatures differently along the migratory flyway and the breeding areas, it is unlikely that arrival dates are advanced at the same rate as the timing of breeding should advance, given the advancement of the underlying levels of the food chain.     

Arrival and onset of breeding of three passerine birds in eastern Finland tracks climatic variation and phenology of insects

Anthropogenic climate change poses a challenge to the annual cycles of migratory birds. It has become urgent to understand whether migratory birds are able to advance their spring phenology when the climate is warming and whether they are able to adjust these phenological phases to the spring phenology in their breeding areas. In this work, we studied long‐term trends in first arrival and onset of breeding for three passerine birds in eastern Finland; the pied flycatcher Ficedula hypoleuca, the common redstart Phoenicurus phoenicurus and the great tit Parus major. The pied flycatcher and the common redstart are long‐distance migrants while the great tit is a partial migrant in Finland. We asked what environmental variables best explain the first arrival or onset of breeding, if there is evidence of ‘thermal delay’ (long‐term increase in the accumulated temperatures) at arrival or onset of breeding and if the interannual variation in the onset of breeding correlates with variation in spring phenology of local insects. We found that the pied flycatcher and the common redstart had advanced their first arrival (explained by increased temperatures at the migration route), but we found no long‐term change in the onset of breeding (explained by local temperatures). Also, the onset of breeding of the great tit is tracking local temperatures. We found no or only weak evidence of thermal delay at arrival or onset of breeding for any of the species. The onsets of breeding for the pied flycatcher and the great tit are also closely tracking the spring phenology of the local insects. The stable or increasing population sizes of all three species in Finland could be a result from their ability to effectively track climatic and environmental variation.     

Climatic patterns in the establishment of wintering areas by North American migratory birds

Long‐distance migration in birds is relatively well studied in nature; however, one aspect of this phenomenon that remains poorly understood is the pattern of distribution presented by species during arrival to and establishment of wintering areas. Some studies suggest that the selection of areas in winter is somehow determined by climate, given its influence on both the distribution of bird species and their resources. We analyzed whether different migrant passerine species of North America present climatic preferences during arrival to and departure from their wintering areas. We used ecological niche modeling to generate monthly potential climatic distributions for 13 migratory bird species during the winter season by combining the locations recorded per month with four environmental layers. We calculated monthly coefficients of climate variation and then compared two GLM (generalized linear models), evaluated with the AIC (Akaike information criterion), to describe how these coefficients varied over the course of the season, as a measure of the patterns of establishment in the wintering areas. For 11 species, the sites show nonlinear patterns of variation in climatic preferences, with low coefficients of variation at the beginning and end of the season and higher values found in the intermediate months. The remaining two species analyzed showed a different climatic pattern of selective establishment of wintering areas, probably due to taxonomic discrepancy, which would affect their modeled winter distribution. Patterns of establishment of wintering areas in the species showed a climatic preference at the macroscale, suggesting that individuals of several species actively select wintering areas that meet specific climatic conditions. This probably gives them an advantage over the winter and during the return to breeding areas. As these areas become full of migrants, alternative suboptimal sites are occupied. Nonrandom winter area selection may also have consequences for the conservation of migratory bird species, particularly under a scenario of climate change.     

The migration of the great snipe Gallinago media: intriguing variations on a grand theme

The migration of the great snipe Gallinago media was previously poorly known. Three tracks in 2010 suggested a remarkable migratory behaviour including long and fast overland non‐stop flights. Here we present the migration pattern of Swedish male great snipes, based on 19 individuals tracked by light‐level geolocators in four different years. About half of the birds made stopover(s) in northern Europe in early autumn. They left the breeding area 15 d earlier than those which flew directly to sub‐Sahara, suggesting two distinct autumn migration strategies. The autumn trans‐Sahara flights were on average 5500 km long, lasted 64 h, and were flown at ground speeds of 25 m s^?1 (90 km h^?1). The arrival in the Sahel zone of west Africa coincided with the wet season there, and the birds stayed for on average three weeks. The birds arrived at their wintering grounds around the lower stretches of the Congo River in late September and stayed for seven months. In spring the great snipes made trans‐Sahara flights of similar length and speed as in autumn, but the remaining migration through eastern Europe was notably slow. All birds returned to the breeding grounds within one week around mid‐May. The annual cycle was characterized by relaxed temporal synchronization between individuals during the autumn–winter period, with maximum variation at the arrival in the wintering area. Synchronization increased in spring, with minimum time variation at arrival in the breeding area. This suggests that arrival date in the breeding area is under strong stabilizing selection, while there is room for more flexibility in autumn and arrival to the wintering area. The details of the fast non‐stop flights remain to be elucidated, but the identification of the main stopover and wintering areas is important for future conservation work on this red‐listed bird species.     

Climate warming,ecological mismatch at arrival and population decline in migratory birds

Climate is changing at a fast pace, causing widespread, profound consequences for living organisms. Failure to adjust the timing of life-cycle events to climate may jeopardize populations by causing ecological mismatches to the life cycle of other species and abiotic factors. Population declines of some migratory birds breeding in Europe have been suggested to depend on their inability to adjust migration phenology so as to keep track of advancement of spring events at their breeding grounds. In fact, several migrants have advanced their spring arrival date, but whether such advancement has been sufficient to compensate for temporal shift in spring phenophases or, conversely, birds have become ecologically mismatched, is still an unanswered question, with very few exceptions. We used a novel approach based on accumulated winter and spring temperatures (degree-days) as a proxy for timing of spring biological events to test if the progress of spring at arrival to the breeding areas by 117 European migratory bird species has changed over the past five decades. Migrants, and particularly those wintering in sub-Saharan Africa, now arrive at higher degree-days and may have therefore accumulated a ‘thermal delay’, thus possibly becoming increasingly mismatched to spring phenology. Species with greater ‘thermal delay’ have shown larger population decline, and this evidence was not confounded by concomitant ecological factors or by phylogenetic effects. These findings provide general support to the largely untested hypotheses that migratory birds are becoming ecologically mismatched and that failure to respond to climate change can have severe negative impacts on their populations. The novel approach we adopted can be extended to the analysis of ecological consequences of phenological response to climate change by other taxa.     

Sex and age-specific differences in wing pointedness and wing length in blackcaps Sylvia atricapilla migrating through the southern Baltic coast

The blackcap Sylvia atricapilla shows a complex migratory pattern and is a suitable species for the studies of morphological migratory syndrome, including adaptations of wing shape to different migratory performance. Obligate migrants of this species that breed in northern, central, and Eastern Europe differ by migration distance and some cover shorter distance to the wintering grounds in the southern part of Europe/North Africa or the British Isles, although others migrate to sub-Saharan Africa. Based on ˃40 years of ringing data on blackcaps captured during autumn migration in the Southern Baltic region, we studied age- and sex-related correlations in wing pointedness and wing length of obligate blackcap migrants to understand the differences in migratory behavior of this species. Even though the recoveries of blackcaps were scarce, we reported some evidence that individuals which differ in migration distance differed also in wing length. We found that wing pointedness significantly increased with an increasing wing length of migrating birds, and adults had longer and more pointed wings than juvenile birds. This indicates stronger antipredator adaptation in juvenile blackcaps than selection on flight efficiency, which is particularly important during migration. Moreover, we documented more pronounced differences in wing length between adult and juvenile males and females. Such differences in wing length may enhance a faster speed of adult male blackcaps along the spring migration route and may be adaptive when taking into account climatic effects, which favor earlier arrival from migration to the breeding grounds.     

Spring arrival response to climate change in birds: a case study from eastern Europe

This paper analyses the dependence of the first spring arrival dates of short/medium- and long-distance migrant bird species on climate warming in eastern Europe. The timing of arrival of the selected species at the observation site correlates with the North Atlantic Oscillation (NAO) index, air temperature, atmospheric pressure, precipitation and wind characteristics. A positive correlation of fluctuations in winter and spring air temperatures with variations in the NAO index has been established in eastern Europe. Positive winter NAO index values are related to earlier spring arrival of birds in the eastern Baltic region and vice versa—arrival is late when the NAO index is negative. The impact of climate warming on the bird’s life cycle depends on local or regional climate characteristics. We tested the hypothesis that differences in climate indices between North Africa and Europe can influence the timing of spring arrival. Our results support the hypothesis that differences in first spring arrival dates between European populations occur after individuals cross the Sahara. We assume that the endogenous programme of migration control in short/medium-distance migrants synchronises with the changing environment on their wintering grounds and along their migration routes, whereas in long-distance migrants it is rather with environmental changes in the second part of their migratory route in Europe. Our results strongly indicate that the mechanism of dynamic balance in the interaction between the endogenous regulatory programme and environmental factors determines the pattern of spring arrival, as well as migration timing.     

Central European Greylag Geese Anser anser show a shortening of migration distance and earlier spring arrival over 60 years

Global climate change can cause pronounced changes in species? migratory behaviour. Numerous recent studies have demonstrated climate‐driven changes in migration distance and spring arrival date in waterbirds, but detailed studies based on long‐term records of individual recapture or re‐sighting events are scarce. Using re‐sighting data from 430 marked individuals spanning a 60‐year period (winters 1956/1957 to 2015/2016), we assessed patterns in migration distance and spring arrival date, wintering‐site fidelity and survival in the increasing central European breeding population of Greylag Geese Anser anser. We demonstrate a long‐term decrease in migration distance, changes in the wintering range caused by winter partial short‐stopping, and the earlier arrival of geese on their breeding grounds. Greylag Geese marked on central Europe moulting grounds have not been recorded wintering in Spain since 1986 or in Tunisia and Algeria since 2004. The migration distance and spring arrival of geese indicated an effect of temperature at the breeding site and values of the NAO index. Greylag Geese migrate shorter distances and arrive earlier in milder winters. We suggest that shifts in the migratory behaviour of Central European Greylag Geese are individual temperature‐dependent decisions to take advantage of wintering grounds becoming more favourable closer to their breeding grounds, allowing birds to acquire breeding territories earlier.     

Winter rainfall predicts phenology in widely separated populations of a migrant songbird

Climate change is affecting behaviour and phenology in many animals. In migratory birds, weather patterns both at breeding and at non-breeding sites can influence the timing of spring migration and breeding. However, variation in responses to weather across a species range has rarely been studied, particularly among populations that may winter in different locations. We used prior knowledge of migratory connectivity to test the influence of weather from predicted non-breeding sites on bird phenology in two breeding populations of a long-distance migratory bird species separated by 3,000 km. We found that winter rainfall showed similar associations with arrival and egg-laying dates in separate breeding populations on an east–west axis: greater rainfall in Jamaica and eastern Mexico was generally associated with advanced American redstart (Setophaga ruticilla) phenology in Ontario and Alberta, respectively. In Ontario, these patterns of response could largely be explained by changes in the behaviour of individual birds, i.e., phenotypic plasticity. By explicitly incorporating migratory connectivity into responses to climate, our data suggest that widely separated breeding populations can show independent and geographically specific associations with changing weather conditions. The tendency of individuals to delay migration and breeding following dry winters could result in population declines due to predicted drying trends in tropical areas and the tight linkage between early arrival/breeding and reproductive success in long-distance migrants.     

Patterns of bird migration phenology in South Africa suggest northern hemisphere climate as the most consistent driver of change

Current knowledge of phenological shifts in Palearctic bird migration is largely based on data collected on migrants at their breeding grounds; little is known about the phenology of these birds at their nonbreeding grounds, and even less about that of intra‐African migrants. Because climate change patterns are not uniform across the globe, we can expect regional disparities in bird phenological responses. It is also likely that they vary across species, as species show differences in the strength of affinities they have with particular habitats and environments. Here, we examine the arrival and departure of nine Palearctic and seven intra‐African migratory species in the central Highveld of South Africa, where the former spend their nonbreeding season and the latter their breeding season. Using novel analytical methods based on bird atlas data, we show phenological shifts in migration of five species – red‐backed shrike, spotted flycatcher, common sandpiper, white‐winged tern (Palearctic migrants), and diederik cuckoo (intra‐African migrant) – between two atlas periods: 1987–1991 and 2007–2012. During this time period, Palearctic migrants advanced their departure from their South African nonbreeding grounds. This trend was mainly driven by waterbirds. No consistent changes were observed for intra‐African migrants. Our results suggest that the most consistent drivers of migration phenological shifts act in the northern hemisphere, probably at the breeding grounds.     

Light‐level geolocators reveal migratory connectivity in European populations of pied flycatchers Ficedula hypoleuca

Understanding what drives or prevents long‐distance migrants to respond to environmental change requires basic knowledge about the wintering and breeding grounds, and the timing of movements between them. Both strong and weak migratory connectivity have been reported for Palearctic passerines wintering in Africa, but this remains unknown for most species. We investigated whether pied flycatchers Ficedula hypoleuca from different breeding populations also differ in wintering locations in west‐Africa. Light‐level geolocator data revealed that flycatchers from different breeding populations travelled to different wintering sites, despite similarity in routes during most of the autumn migration. We found support for strong migratory connectivity showing an unexpected pattern: individuals breeding in Fennoscandia (S‐Finland and S‐Norway) wintered further west compared to individuals breeding at more southern latitudes in the Netherlands and SW‐United Kingdom. The same pattern was found in ring recovery data from sub‐Saharan Africa of individuals with confirmed breeding origin. Furthermore, population‐specific migratory connectivity was associated with geographical variation in breeding and migration phenology: birds from populations which breed and migrate earlier wintered further east than birds from ‘late’ populations. There was no indication that wintering locations were affected by geolocation deployment, as we found high repeatability and consistency in δ¹³C and δ¹⁵N stable isotope ratios of winter grown feathers of individuals with and without a geolocator. We discuss the potential ecological factors causing such an unexpected pattern of migratory connectivity. We hypothesise that population differences in wintering longitudes of pied flycatchers result from geographical variation in breeding phenology and the timing of fuelling for spring migration at the wintering grounds. Future research should aim at describing how temporal dynamics in food availability across the wintering range affects migration, wintering distribution and populations’ capacity to respond to environmental changes.