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The seasonal timing of moult in migratory birds is an adaptation to cope with time constraints in the annual cycle. Kiat and Izhaki analysed moult patterns in Palaearctic passerines and rejected the proposition that seasonally divided moult is an endogenously controlled strategy. Instead, they advocated the view that it occurs due to a flexible and opportunistic timing of moult. In contrast, we argue that Kiat and Izhaki's analysis is flawed and that they overlooked several important facts about moult in the Barred Warbler Sylvia nisoria and other species showing seasonally divided moult. These include the facts that juveniles replace a few secondaries already in their first winter, and that the moult sequences of primaries and secondaries are decoupled compared with the typical passerine complete moult sequence. We argue that seasonally divided moult is an adaptive strategy that is largely under endogenous control. [ABSTRACT FROM AUTHOR]

Biological rhythms of nearly all animals on earth are synchronized with natural light and are aligned to day‐and‐night transitions. Here, we test the hypothesis that the lunar cycle affects the nocturnal flight activity of European Nightjars (Caprimulgus europaeus). We describe daily activity patterns of individuals from three different countries across a wide geographic area, during two discrete periods in the annual cycle. Although the sample size for two of our study sites is small, the results are clear in that on average individual flight activity was strongly correlated with both local variation in day length and with the lunar cycle. We highlight the species' sensitivity to changes in ambient light and its flexibility to respond to such changes in different parts of the world. [ABSTRACT FROM AUTHOR]

Vector navigation, i.e. maintaining a constant heading for a given amount of time, is hypothesized to provide a viable basis for the navigational feats of a number of long-distance animal migrants. Since animals following this strategy are subject to drift by wind or by ocean current, performing long migrations relying on vector navigation is particularly challenging. We tested whether vector navigation could be involved in the migrations of green turtles (Chelonia mydas) that migrate between the remote Ascension Island and Brazil. To this aim, a novel approach was followed using individual-based numerical models to simulate migratory trajectories of virtual turtles that were compared to actual routes reconstructed by satellite. Simulated postnesting migrations from Ascension revealed that weak currents enabled modeled turtles to reach the Brazilian coast, but only for a limited range of headings around due West. This conclusion was corroborated by comparing modeled trajectories with the actual routes of previously tracked turtles, with a beeline vector navigation strategy providing the best fit, although a true-navigation strategy directed to the landfall site produced similar results. Finally, we tested if a vector navigational strategy was feasible for the prebreeding migration from Brazil towards Ascension, but modeled routes mostly failed to reach the island or a larger area around it, with individuals drifting away under the influence of currents. We conclude that Ascension turtles can take advantage of vector navigation when migrating towards a wide target like the Brazilian coast, while the demanding prebreeding migration likely requires more complex navigational systems. [ABSTRACT FROM AUTHOR]

The selection of flight speed (airspeed) in migrating birds depends on multiple internal and external factors, such as wing morphology, weight and winds. Adjustment with respect to side winds to maintain an intended track direction may include a shift in heading direction and/or an increase in airspeed. Compensation for cross-winds cannot always be achieved if visual references are lacking or may not even be beneficial if adaptive wind drift is favourable. Flock size is an additional, although often neglected, factor that could influence the airspeed of birds. Here, we show that responses to cross-winds to achieve compensation differed on a small geographical scale (a few kilometres) in migrating shorebirds, where the availability of topographical features such as coastlines may play an important role for the birds' behaviour. We also show that airspeed was significantly influenced by flock size in three species of shorebirds, increasing with increasing flock size. This is contrary to the prediction based on the hypothesis of energy saving by flight in flock formation, but in agreement with empirical findings for migrating terns. The reason why flock size influences airspeed remains unclear, but we propose a mechanistic explanation based on the largest/heaviest individual(s) determining the speed of the flock. [ABSTRACT FROM AUTHOR]

It is well established that differences in migratory behavior between populations of songbirds have a genetic basis but the actual genes underlying these traits remains largely unknown. In an attempt to identify such candidate genes we de novo assembled the genome of the willow warbler Phylloscopus trochilus, and used whole‐genome resequencing and a SNP array to associate genomic variation with migratory phenotypes across two migratory divides around the Baltic Sea that separate SW migrating P. t. trochilus wintering in western Africa and SSE migrating P. t. acredula wintering in eastern and southern Africa. We found that the genomes of the two migratory phenotypes lack clear differences except for three highly differentiated regions located on chromosomes 1, 3, and 5 (containing 146, 135, and 53 genes, respectively). Within each migratory phenotype we found virtually no differences in allele frequencies for thousands of SNPs, even when comparing geographically distant populations breeding in Scandinavia and Far East Russia (>6000 km). In each of the three differentiated regions, multidimensional scaling‐based clustering of SNP genotypes from more than 1100 individuals demonstrates the presence of distinct haplotype clusters that are associated with each migratory phenotype. In turn, this suggests that recombination is absent or rare between haplotypes, which could be explained by inversion polymorphisms. Whereas SNP alleles on chromosome 3 correlate with breeding altitude and latitude, the allele distribution within the regions on chromosomes 1 and 5 perfectly matches the geographical distribution of the migratory phenotypes. The most differentiated 10 kb windows and missense mutations within these differentiated regions are associated with genes involved in fatty acid synthesis, possibly representing physiological adaptations to the different migratory strategies. The ∼200 genes in these regions, of which several lack described function, will direct future experimental and comparative studies in the search for genes that underlie important migratory traits. [ABSTRACT FROM AUTHOR]

Migratory birds are known to be capable of adjusting their heading direction to compensate for wind drift and their airspeed adaptively with respect to head and tail winds. High-flying nocturnally migrating common swifts, Apus apus , have been shown to compensate for wind drift, but they failed to adjust airspeed as expected (increase in head wind and decrease in tail wind in relation to neutral wind). We report on new measurements of diurnally migrating common swifts at a coastal site in the Baltic, where the birds did adjust airspeed adaptively during spring and autumn migration. During autumn migration, they compensated for lateral wind drift by adjusting heading direction similarly to high-altitude migrants in autumn. We also recorded flight speed and wind compensation during a summer weather-related exodus, when the birds behaved similarly to those during autumn migration, although they showed a small degree of wind drift. Why birds failed to adjust airspeed adaptively at high altitude is discussed, and we argue there is a threshold in the sensory system to detect small changes in optic flow based on visual landmarks. [ABSTRACT FROM AUTHOR]

Flight is an economical mode of locomotion, because it is both fast and relatively cheap per unit of distance, enabling birds to migrate long distances and obtain food over large areas. The power required to fly follows a U-shaped function in relation to airspeed, from which context dependent 'optimal' flight speeds can be derived. Crosswinds will displace birds away from their intended track unless they make compensatory adjustments of heading and airspeed. We report on flight track measurements in five geometrically similar tern species ranging one magnitude in body mass, from both migration and the breeding season at the island of Öland in the Baltic Sea. When leaving the southern point of Öland, migrating Arctic and common terns made a 60° shift in track direction, probably guided by a distant landmark. Terns adjusted both airspeed and heading in relation to tail and side wind, where coastlines facilitated compensation. Airspeed also depended on ecological context (searching versus not searching for food), and it increased with flock size. Species-specific maximum range speed agreed with predicted speeds from a new aerodynamic theory. Our study shows that the selection of airspeed is a behavioural trait that depended on a complex blend of internal and external factors. [ABSTRACT FROM AUTHOR]

The Sahara Desert is one of the largest land-based barriers on the Earth, crossed twice each year by billions of birds on migration. Here we investigate how common swifts migrating between breeding sites in Sweden and wintering areas in sub-Saharan Africa perform the desert crossing with respect to route choice, winds, timing and speed of migration by analysing 72 geolocator tracks recording migration. The swifts crosswestern Sahara on a broad front in autumn, while in spring they seem to use three alternative routes across the Sahara, awestern, a central and an eastern route across the Arabian Peninsula, with most birds using the western route. The swifts show slower migration and travel speeds, and make longer detours with more stops in autumn compared with spring. In spring, the stopover period inWest Africa coincided with mostly favourable winds, but birds remained in the area, suggesting fuelling. The western route provided more tailwind assistance compared with the central route for our tracked swifts in spring, but not in autumn. The ultimate explanation for the evolution of a preferred western route is presumably a combination of matching rich foraging conditions (swarming insects) and favourable winds enabling fast spring migration. [ABSTRACT FROM AUTHOR]

In many migratory birds, males precede females during migration and arrival at the breeding sites. Three proximate mechanisms are proposed to explain this phenomenon of protandry: males 1) winter closer to breeding sites, 2) start spring migration earlier, and/or 3) migrate faster than females. So far, the relative contribution of these mechanisms to protandry is unknown. The present study investigated the importance of each of the 3 proximate mechanisms of protandry for a songbird migrant wintering in Africa, the northern wheatear (Oenanthe oenanthe). Two subspecies co-occur in Europe on migration, of which the leucorhoa northern wheatears breeding from Iceland to Canada have to cross the North Atlantic, whereas the nominate form breeding in Europe does not face any significant sea barrier. We show that the leucorhoa subspecies had a significantly higher degree of protandry at stopover sites across Europe than the oenanthe subspecies (-6 vs. -2 days). Leucorhoa northern wheatear's higher degree of protandry was associated with a larger age effect, in which old males preceded young males, and greater sex-specific differences in wing shape and refueling yielding higher migration speeds in males than females. In oenanthe northern wheatears, light-level geolocators revealed that males did not winter closer to the breeding sites or migrate faster than females, but initiated spring migration earlier. Our results demonstrate that the significance of the mechanisms causing protandry can differ between related taxa and highlight the importance of the advancement in male arrival date with age as a potential factor shaping the degree of protandry. [ABSTRACT FROM AUTHOR]

Circular orientation cages have been used for several decades to record the migratory orientation of passerine migrants, and have been central to the investigation of the functional characteristics of the biological compasses used for orientation. The use of these cages offers unique possibilities to study the migratory behaviour of songbirds, but suffers from statistical limitations in evaluating the directions of the activity recorded in the cages. The migratory activity has been reported to vary, including complex multimodal orientation of migratory passerines tested in orientation cages irrespective of species studied. The currently applied circular statistical methods fail to describe orientation responses differing from unimodal and axial distributions. We propose for the first time a modelling procedure enabling the analysis of multimodal distributions at either an individual or a group level. In this paper we compare the results of conventional methods and the recommended modelling approach. Migratory routes may be more complex than a simple migratory direction, and multimodal behaviour in migratory species at the individual and population levels can be advantageous. Individuals may select the expected migratory direction, but may also return to safer sites en route, i.e. sites already known, which provide food and/or shelter in reverse directions. In individual birds, several directions may be expressed in the same test hour. At the species level, multimodal orientation may give an opportunity to expand the range or may refer to differential migration route preferences in different populations of birds. A conflicting experimental situation may also result in a different preferential orientation. In this paper we suggest a statistical solution to deal with these types of variations in orientation preference. [ABSTRACT FROM AUTHOR]

1. The genetic differentiation in a migratory butterfly, the red admiral ( Vanessa atalanta), was investigated to discern patterns of migratory routes used across Europe. AFLP profiles showed significant differences between almost all sampled locations, but there was no clear pattern of isolation-by-distance. 2. Using the software STRUCTURE 2.2, we found two distinct genotype clusters present in different frequencies at all study sites. The frequencies of these genotypic clusters varied significantly between years within the same site. Remarkably few individuals were of mixed ancestry, indicating that some isolating mechanisms are present. Twenty-seven mtDNA haplotypes were identified but they showed no geographic structure, nor were they related to either of the two genotype clusters identified in the AFLP data. 3. Most field observations of migrating red admirals suggest a regular north–south migration pattern in Europe. Our data indicate both long-distance migration and a more variable pattern in orientation, since the composition of the two genotypic clusters shows dramatic variation between sites and years in the northern part of the distribution range. [ABSTRACT FROM AUTHOR]

The circular distribution of the willow warbler Phylloscopus trochilus around the Baltic Sea shares many features with the classic examples of ring species; however, the system is much younger. It has previously been shown that a secondary contact zone is located in central Scandinavia, where there are narrow clines for several morphological traits coincident with a migratory divide. Here we analyse multiple traits and genes from > 1700 males captured on breeding territories at 77 sites spread around the Baltic Sea to test the following hypothesis. If the secondary contact zone in Scandinavia is a result of divergence in two allopatric refuge populations during the last glaciation, we expect to find a similar secondary contact zone somewhere else around the circular distribution. Our results show that the trait clines were wider and displaced from each other along the eastern side of the Baltic Sea. Analyses of 12 microsatellite loci confirmed that the genome is very similar between the terminal forms ( FST = 0). Two AFLP-derived markers filtered out from a genomic scan instead appear to be maintained by selection. These markers exhibited steep clines at the secondary contact zone in Scandinavia, but as for the phenotypic traits, had vastly different cline centres east of the Baltic Sea. The trait clines along the ring distribution outside the Scandinavian secondary contact zone thus seem to have been shaped by independent action of selection or drift during the process of postglacial colonization. [ABSTRACT FROM AUTHOR]

Many migratory animals use daylength, or photoperiod, to signal when to migrate and transition between annual phenological states. Whether animals use photoperiod as a temporal or spatial cue while migrating, however, requires additional empirical support. We used hatch-year dunnocks, Prunella modularis (a songbird), caught during their first migration in southern Sweden to elucidate whether migratory animals incorporate photoperiod as a spatiotemporal cue into their endogenous migratory program during migration. We exposed the migratory-naïve to light environments that simulated either the local photic conditions or a shorter daylength and larger transitions between photoperiods. All birds experienced local geomagnetic conditions. We hypothesized that migratory dunnocks used photoperiod to inform their first migration and predicted that the experimental treatment represented either a spatial displacement to the north or a temporal advancement towards winter at the capture site compared to the local control conditions. We found, though, that the short photoperiods terminated the expression of the migratory phenotype compared to controls by reducing body mass gain and ending migratory activity, indicating that the endogenous migratory program integrates photoperiod during migration. The incorporation of photoperiod into the endogenous program may complement geomagnetic cues to ensure ending migration at the correct time and location. The incorporation of photoperiod can also provide a mechanism that facilitates poleward shifts of overwintering distribution under climate change by allowing migrants to overwinter in newly suitable habitat at higher latitude (i.e. short stopping). • Short photoperiods end migratory activity and reduce migratory gain in body mass. • The endogenous migratory program incorporates photoperiod as a spatiotemporal cue. • Photic and geomagnetic cues may complement each other during migration. • Response to short photoperiods may facilitate short-stopping migration. [ABSTRACT FROM AUTHOR]

Flight activity recorders have recently confirmed that alpine and common swifts spend the majority of their non‐breeding period on the wing, which may last 6–10 months. Here we test the hypothesis that the closely related pallid swift, a species with a breeding distribution around the Mediterranean, lead a similar aerial life‐style during its migration and wintering periods. The pallid swift usually lays two clutches in one season and therefore spends more time in the breeding area than the common swift. We successfully tracked four pallid swifts with data loggers that record light for geolocation and acceleration every 5 min to monitor flight activity. The birds wintered south of the Sahel in west Africa from the Ivory Coast to Cameroon. The pallid swifts spent the majority of their non‐breeding time in flight, especially the first two months after leaving the breeding area in autumn, while a few landing events occurred during the winter. The total time grounded was < 1%, similar to that of the common and alpine swifts. The mass specific flight metabolic rate of swifts is similar to the average non‐breeding metabolic rate of a long distance terrestrial migrant, suggesting swifts are not more likely to procure oxidative damage as a consequence of continuous flight than other migrants. The open airspace used by swifts may provide a relatively safe habitat that explain the high survival rate found in swifts. [ABSTRACT FROM AUTHOR]

Many animals have evolved a migratory lifestyle as an adaptation to seasonality, 1,2 ranging from insects 3 to fish, 4 terrestrial and marine mammals, 5–7 and birds. 8 Old World swifts have evolved an extraordinary aerial non-breeding life phase lasting for 6–10 months. 9–11 Swifts exploit the aerosphere in search of insects to meet the high energy demands of flight. 12 During this period they roost and likely also sleep in the open airspace. Nocturnal insectivores with restricted foraging time may use moonlight to increase energy intake. 13 Using multisensor data loggers that record light for geolocation, acceleration for flight activity, and pressure for flight altitude, we investigated if Northern black swifts, Cypseloides niger borealis , breeding in North America, also lead an aerial lifestyle similar to their Old World relatives. Individual flight activity showed they are airborne >99% of the time, with only occasional landings during their 8-month non-breeding period. Unexpectedly, during periods around the full moon, they conducted regular nocturnal ascents to altitudes up to >4,000 m (mean 2,000 m). A lunar eclipse triggered a synchronized descent, showing a direct effect of moonlight on flight altitude. This previously unknown behavior of nocturnal ascents during moonlight nights could be either a response to predator avoidance or that moonlight provides a foraging opportunity. Observed elevated nocturnal flight activity during periods of moonlight compared to dark nights suggests swifts were hawking for prey. Our finding of this novel behavior provides new perspectives on nocturnal flight behavior during periods surrounding the full moon. [Display omitted] • Black swifts are airborne for up to 8 months during their non-breeding period • During nights around full moon, black swifts ascended to altitudes of 2–4,000 m • Flight behavior during full moon nights suggests the swifts were actively foraging • During a lunar eclipse the birds responded by immediately losing altitude Migrating black swifts remain airborne for up to 8 months. Hedenström et al. show that they climb to 4,000 m and remain at 2,000 m during periods around full moon, when moonlight likely allows feeding on aerial insects. A lunar eclipse catalyzed a synchronized rapid descent by the swifts, showing the direct influence of light on their behavior. [ABSTRACT FROM AUTHOR]

Each autumn, large numbers of red admirals migrate throughout northern Europe, flying south, to reach areas with conditions suitable for surviving the winter. We observed the visible butterfly migration at Falsterbo peninsula, the southwesternmost point in Sweden, where red admirals are seen most autumns flying towards the Danish coast on their way to more southern parts of Europe. Weather parameters from a local weather station were used to analyse what factors are important for red admiral migration across the sea. Wind direction was among the important weather variables affecting the initiation of the migratory departure; most other studies of butterfly migration reported no large effect of wind direction. This difference is probably because the butterflies in our study were about to cross open sea for more than 20km, whereas most previous studies were from inland locations where butterflies could avoid wind effects by flying close to the ground or on the lee side of topographical features. Other important weather variables affecting red admiral migration at Falsterbo were low wind speed and clear skies. The flight direction at Falsterbo was towards the west, which is in contrast to the southward direction generally reported during autumn migration in this species. This is probably because the red admirals followed both the local topography and the closest route to land on the other side and therefore deviated from the normally preferred direction to minimize flight over open water. [Copyright &y& Elsevier]