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Weather ultimately affects avian migration. The significance of meteorological variables is relatively well known for flights of migrants and for departure/landing decisions at stopover sites. Success of migration greatly depends on storage of fat and body mass gain at stopovers; however, the influence of weather on refueling at stopovers is surprisingly poorly studied. We tested the hypothesis that body mass change of European Robins during their migratory stopovers is affected by meteorological factors (air temperature, precipitations, surface wind speed), along with other ecological variables. We used data on body mass change in 9743 individuals (5147in spring and 4587 in the fall) captured and recaptured within the same day on the Courish Spit of the Baltic Sea in 1994–2003. Fuel deposition rate in Robins was positively associated with air temperature and with higher amount of precipitation. Wind speed did not influence the refueling efficiency of our study species. Also, fuel deposition rate of Robins was affected by age (higher in adults than in first-year birds), negatively influenced by the number of conspecifics at stopover, influenced by the progress of the season (negatively in spring and positively in fall), and negatively influenced by initial energy reserves of migrants, when birds in poor energy condition were more likely to gain weight than birds with large fuel stores. This study shows that refueling of Robins on migration stopovers is substantially affected by meteorological factors that should be taken in to account for comprehensive understanding of stopover ecology and migration strategy of songbird migrants.

After completing a night migratory flight in the morning, European Robins begin to make search movements to find a stopover for rest and replenishment of their energy resources. The data on the capture of 111 European Robins during the spring migration on the Courish Spit of the Baltic Sea show that the speed of movement of birds during the search does not depend on air temperature, wind speed, rainfall, or the number of conspecific individuals at the stopover. It is to a small extent affected by the age and energy state of birds, as well as the calendar date. It is assumed that the most powerful influence on the speed of search movements of European Robins in spring is exerted by the endogenous programs for finding stopovers, which differ greatly among individual birds.

Ecological “big data” Human activities are rapidly altering the natural world. Nowhere is this more evident, perhaps, than in the Arctic, yet this region remains one of the most remote and difficult to study. Researchers have increasingly relied on animal tracking data in these regions to understand individual species' responses, but if we want to understand larger-scale change, we need to integrate our understanding across species. Davidson et al. introduce an open-source data archive that currently hosts more than 15 million location data points across 96 species and use it to show distinct climate change responses across species. Such ecological “big data” can lead to a wider understanding of change. Science , this issue p. 712

Compensation for wind drift in relation to the side-wind velocity and altitude was investigated in Song Thrushes during autumn migration. The birds were recorded at night flying above the prominent leading line of a marine spit which coincided with the general direction of their migration. Among the large size passerine species, Song Thrushes were identified by a combination of five flight characteristics typical only of this species during particular periods of autumn. The thrushes showed different reactions to the crosswinds: complete and partial compensation for the displacement and drift. Under normal visibility, the completeness of compensation depended both on the velocity of the side-wind and altitude. The degree of compensation achieved was reduced with an increase of altitude, regardless of the wind. Under the same wind conditions, the angle of drift (the angle between the track direction and the leading line) increased with altitude, but the number of birds that compensated for drift decreased. On average, at heights below 300 m agl, the thrushes were capable of compensating completely for moderate winds; between 300 and 600 m agl compensation was partial; but above 600 m the birds drifted completely. Birds of the same species flying above the same terrain may demonstrate different reactions to the same crosswind depending on altitude. Meanwhile, flight tracks gradually deviated from the leading line with an increase in altitude, the headings of the birds got closer to the general migratory direction. It is more likely that the birds control displacement using the visual flow regulation principle by the angular velocity of the landmarks below them running aside in relation to their flight direction, which is inversely proportional to the altitude. Low flying thrushes promptly reacted to the shifting of the leading line of the spit with an average angular velocity of more than 0.8°/s perpendicular to the direction of flight and compensated completely for drift. Shifting of the leading line with an angular velocity of less than 0.4°/s, the high flying birds did not seem to notice or did not try to compensate for displacement deliberately.

Analysis of factors that influence stopover departure decisions in migrating birds is an important step in understanding their movements. We studied body condition, refuelling efficiency and weather during arrival and subsequent departure of migrant European Robins Erithacus rubecula at a stopover site on the Courish Spit (Eastern Baltic) to explain why some birds continued migration on the night following arrival (‘transients’) while others stopped over for a more prolonged period (‘non-transients’). Analysis of 125 uniquely recaptured birds showed that long stopovers could not explained by adverse weather during the night following arrival. Comparison of arrival fuel loads in ‘transient’ and ‘non-transient’ individuals revealed no clear differences and most birds were able to gain mass. Only the combined consideration of both energetic and weather parameters showed that departure decisions depended on simultaneous action of nearly all factors. In ‘non-transient’ birds, the exact stopover duration is governed by a combination of achieved fuel deposition rate/fuel stores and the prevailing weather pattern. In spring, European Robins selected optimal wind condition to start a new flight bout while in autumn they departed under moderately unfavorable winds.

Time of departure and landing of nocturnal migrants are of great importance for understanding migratory strategy used by birds. It allows us to estimate flying time and hence the distance that migrants cover during a single night. In this paper, I studied the temporal schedule of nocturnal departures of European robins during spring migration. The study was done on the Courish Spit on the Baltic Sea in 1998–2003 by retrapping 51 ringed birds in high mist nets during nocturnal migratory departure. Take-offs of individual birds occurred between the first and tenth hour after sunset (median 176 min after sunset). Departure time was not related to fuel stores at arrival and departure, stopover duration and progress of the season. The results suggest that one reason for temporal variation in take-off time was differential response of European robins with high and low motivation to depart to such triggers as air pressure and its trend. If these parameters reach a certain minimum threshold shortly before sunset, robins with a high migratory motivation take off in the beginning of the night. When air pressure or its trend reaches a maximum, it may trigger to take off later during the night birds with lower initial motivation for departure, including those that have low refuelling efficiency. In regulation of timing of take-offs of robins, an important role is also played by their individual endogenous circadian rhythm of activity which is related to the environment in a complex way.

Many juvenile Reed Warblers perform nocturnal flights before the onset of the autumn migration. In our study we tested the hypothesis that the decision by juvenile Reed Warblers to perform such flights over the natal area during the post-fledging period depends on weather conditions and the phase of the lunar cycle. We analysed the data on nocturnal movements of 26 birds radio-tagged near their natal site on the Courish Spit (SE Baltic coast). We infer from our results that the decision in juvenile Reed Warblers to take off on a nocturnal flight over the natal area is triggered by intrinsic stimuli and depends only very slightly on environmental conditions. Comparison of these data with a previous study of the effect of weather and the lunar cycle on long-distance nocturnal pre-migratory flights by juvenile Reed Warblers suggests that the motivation to leave the natal area at night increases under good visibility and conditions favourable for flight.

We studied the effects of weather and the lunar cycle on long-distance nocturnal pre-migratory flights of Reed Warblers (Acrocephalus scirpaceus). Noturnal tape luring was used to capture the birds, and the study was carried out in a habitat atypical of this species on the Courish Spit (southeastern Baltic) between1999 and 2002. A total of 443 juvenile Reed Warblers were captured during 120 nights of trapping. Based on data on the moult and body condition of the birds, it was possible to identify 163 individuals as being on post-fledging movements. More than half of the birds (54.0%) were captured at the end of night during the nautical and civil twilight period; the remaining individuals were caught during the astronomical twilight period and darkest periods of night. Many birds performed pre-migratory flights in the middle of the night, the period during which a large part of the moon was visible. We suggest that the increased visibility under the full moon may provide conditions in which Reed Warblers increase the distance or intensity of nocturnal post-fledging movements. During the entire course of the night, the birds generally preferred to fly under rainless conditions, limited cloud cover and/or in still air. The birds performed flights under winds stronger than 2 m s−1 when the wind was blowing along the axis of the spit. We also suggest that the birds generally fly along the spit. We found a weak but significant relationship between the numbers of Reed Warblers captured during post-fledging movements and the individual weather parameters and their interaction. Our data suggest that endogenous stimuli rather than weather parameters or lunar cycle phase determine the decision of Reed Warblers to undertake pre-migratory long-distance flights at night.

To identify the mechanisms of control of temporal schedule of nocturnal migratory flights in small songbirds in nature, we studied the time of departure in a medium-distance nocturnal migrant, the European robin, on the Courish Spit (southeastern Baltic coast) using radiotelemetry. Exact measurements of departure time in 100 birds (58 in autumn and 42 in spring) showed no fixed time window of nocturnal departures during Evening Nautical Twilight. Take-offs occurred throughout the night and even during Morning Astronomical and Nautical Twilight Periods. Departure time showed no significant difference between clear skies and overcast conditions, and significantly differed between the seasons. The median departure time shifted significantly towards sunset during shorter nights in spring as compared to autumn. In both seasons (1) European robins initiating flight after short (1–2 days) stopovers showed no significant differences in departure time between individuals with small and large fuel stores at arrival; and (2) departure time was significantly related to stopover duration: the longer the birds stayed, the earlier they departed in relation to sunset. Only in spring and after longest stopovers, all departures occurred within a short time window soon after sunset.

How migratory birds decide when to leave a stopover site is important to the understanding of bird migration strategies. Our study looks at how body condition and the weather affect the decision to depart on nocturnal migratory flight. During two autumn migration seasons (2002–2003), we radio tracked 51 first-year European robins, Erithacus rubecula, at a stopover site on the Courish Spit (Eastern Baltic) from the first day after landing until their migratory departure. The tagged robins stopped over for 1–14 days. There was no clear relationship between stopover duration and energetic condition on arrival. Weather conditions (wind, precipitation, and cloud cover) on departure differed measurably between years. In 2002, robins took off mainly under following winds and clear skies. In 2003, there were mainly light head winds and partially cloudy or overcast skies. This could be explained by the year-specific role of weather factors in making the decision to depart. In both years, robins making short (1–2 days) stopovers took off in more varied weather situations than those individuals with long stopovers. This suggests that robins from the former group were more inclined to continue with migration than longer-stay birds that, apart from re-fuelling, could be waiting for favourable weather. The lack of a relationship between stopover duration and body condition and some departures under unfavourable weather conditions suggest that endogenous spatiotemporal programmes may play an important role in controlling stopover duration in robins.

We studied migratory stopovers of nocturnal passerine migrants migrating between the Urals and Siberia and the Near East and Africa (five species) and between European Russia and the Indian subcontinent (two species) in an oasis in the arid belt of the northwestern edge of western Central Asia. In autumn, fuel loads of Blyth's Reed Warblers Acrocephalus dumetorum before their desert crossing were much greater than in Palaearctic‐African migrants, which face a much narrower barrier, and also greater than in conspecifics captured during and after the desert crossing. However, another Indian migrant, the Redbreasted Flycatcher Ficedula parva, had low average fuel stores. In spring, Blyth's Reed Warblers carried less fuel than in autumn, and less than African migrants such as Garden Warblers Sylvia borin in spring. This suggests that the arid belt of western Central Asia is a serious ecological barrier for Palaearctic‐Indian passerine migrants in autumn, but much less of one in spring. Palaearctic‐African mig...

Many passerine medium distance nocturnal migrants take off from stopover sites not only at the beginning of the night, but also in the middle and at the end of the night. In this paper, we tested two explanations for this phenomenon: (1) that departure time is governed by fuel stores, and (2) that departure time is influenced by the weather. The relationship of temporal distribution of migratory nocturnal departures with body condition and weather factors was studied in juvenile European robins (Erithacus rubecula) during autumn migration. The study was done on the Courish Spit on the Baltic Sea in 1997–2003 by retrapping 74 ringed birds in high mist nets during nocturnal migratory departure. Departure time was not related to fuel stores at arrival and departure, stopover duration, fuel deposition rate or progress of the season. Nor did the local weather at departure influence departure time. A possible reason was a large variation in the behaviour of the birds. European robins which made 1-day stopovers arrived and departed during better weather conditions than birds that stopped over for longer periods. In the former cohort, a significant model with four predictors explained 55% of variation in departure time. It is assumed that weather at the night of departure and during the previous night influenced the time of take-offs in these birds. In robins which made long stopovers, departure time is probably governed by their individual endogenous circadian rhythms of activity, which are related to the environment in a complex way.

We provide a test of the hypothesis that most Palaearctic-African migratory passerines breeding to the east of Eastern Europe avoid crossing western deserts of Central Asia during autumn migration and make a detour through the steppes and semi-deserts north of the Caspian Sea. Trapping data at a migratory stopover and moon-watch observations in September 2003 in western Kazakhstan in a semi-desert location 375 km north of the Caspian Sea support this hypothesis.

Body mass and fat reserves of Sedge Warblers (Acrocephalus schoenobaenus) on nocturnal departure and arrival were studied by two methods (capture in high nets and playback of songs) on the Courish Spit (Eastern Baltic, Russia) in spring 1998–2000. The average body mass of departing Sedge Warblers was 13.7 g, and the average body mass of arriving birds was 13.1 g. The difference between arrival and departure masses was not significant. The calculated flight range of departing Sedge Warblers in still air varied from 19 to 665 km, with a mean of 295 km. The high fuel loads of Sedge Warblers on departure and on arrival may be explained by the necessity for Scandinavian populations to cross the Baltic; the risk of drifting out to sea for birds migrating over land; or the general vernal migratory strategy of Sedge Warblers, involving a series of short (4.5–6.2 h) flights on several consecutive nights.

Nocturnal migration of Reed Warblers Acrocephalus scirpaceus was studied by trapping with ‘high nets’ on the Courish Spit (Eastern Baltic) during spring 1998–2000. In spring, Reed Warblers left the stopover site between 45 and 240 min after sunset (median 84 min), although 85% of birds took off between 45 and 120 min after sunset. Birds did not arrive until the fifth hour after sunset; 67% of birds ended their nocturnal flights in the penultimate hour before sunrise, i.e. at dawn. At the moment of migratory departure, the average Reed Warbler body mass was 12.79 ± 0.66 g (n = 60). Average body mass of birds ending migratory flight was 11.69 ± 0.67 g (n = 18). The difference was highly significant. However, more than half of the birds completed migratory flights with a considerable fuel load, and some even had energy stores sufficient for a migratory flight on the next night. The spring migratory strategy of Reed Warblers over Central and Northern Europe probably includes a succession of short migratory flights (4–6 h) during several subsequent nights with 1-day stopovers.

Common cuckoos Cuculus canorus are obligate nest parasites yet young birds reach their distant, species-specific wintering grounds without being able to rely on guidance from experienced conspecifics – in fact they never meet their parents. Naïve marine animals use an inherited navigational map during migration but in inexperienced terrestrial animal migrants unequivocal evidence of navigation is lacking. We present satellite tracking data on common cuckoos experimentally displaced 1,800 km eastward from Rybachy to Kazan. After displacement, both young and adult travelled similarly towards the route of non-displaced control birds. The tracking data demonstrate the potential for young common cuckoos to return to the species-specific migration route after displacement, a response so far reported exclusively in experienced birds. Our results indicate that an inherited map allows first-time migrating cuckoos to locate suitable wintering grounds. This is in contrast to previous studies of solitary terrestrial bird migrants but similar to that reported from the marine environment.