BackgroundFor most Afro-Palearctic migrants, particularly small songbirds, spatiotemporal migration schedules and migratory connectivity remain poorly understood. We mapped migration from breeding through winter of one of the smallest Afro-Palearctic migrants, the willow warbler Phylloscopus trochilus, using geolocators (n = 15).ResultsBirds migrated from North European breeding grounds to West Africa via the Iberian Peninsula following a narrow corridor along the West Coast of Africa. Birds then dispersed across the northern Savannah with termination of migration highly variable among individuals. The termination of migration appeared not to be related to timing, current and previous years’ vegetation conditions or biometrics. During winter, most birds moved southwards to improved vegetation.ConclusionThe willow warblers showed a large, unexpected longitudinal spread in winter sites of more than 3000 km between individuals breeding within a 500 m range resulting in a low degree of connectivity. The large wintering area may well be related to generalist behaviour in the species. Our findings contribute to understanding the link between breeding and wintering ecology in long-distance migratory birds.Electronic supplementary materialThe online version of this article (10.1186/s40462-017-0109-x) contains supplementary material, which is available to authorized users.
Timing of return to the breeding area presumably optimizes breeding output in migrants. How timing affects the other components of fitness — survival, has been comparatively little studied. Returning too early in spring is expected to be associated with high mortality in insectivorous migrants when weather conditions are still unsuitable. Yet, males in particular arrive early to get access to the best territories which have been suggested to cause arrival before it is optimal for their survival. For the outward migration in autumn, timing is presumably less directly associated with reproduction and fitness and how it might affect survival is not well understood. We use data of eight songbird species ringed across Denmark to investigate how timing of return migration in spring and departure migration in autumn close to the breeding areas affects survival for short‐ and long‐distance migrants. Further, we compare survival optimum to the timing of males and females at a stopover site in Denmark in three sexually dimorphic, protandric species. We find a clear relationship between return migration and survival which differs between short‐ and long‐distance migrants: Survival decreases with date for short‐distance migrants and a bell‐shaped relationship, with low survival for earliest and latest individuals, for long‐distance migrants. In protandric species, the majority of males return before survival is optimal, whereas females on average return close to the survival optimum. The pattern of survival in relation to autumn timing is less clear, although a similar bell‐shaped relationship is suggested for long‐distance migrants. Our findings support the predicted mortality consequences of too early return to the breeding grounds and also that selection for early return in males leads to suboptimal migration timing regarding survival.
SummaryChanges in land-use and climate are threatening migratory animals worldwide. In birds, declines have been widely documented in long-distance migrants. However, reasons remain poorly understood due to a lack of basic information regarding migratory birds’ ecology in their non-breeding areas and the effects of current environmental pressures there. We studied bird densities, spatial and territorial behaviour and habitat preference in two different habitat types in northern Ghana, West Africa. We study three common Eurasian-African songbirds (Willow Warbler Phylloscopus trochilus, Melodious Warbler Hippolais polyglotta and Pied Flycatcher Ficedula hypoleuca) in a forested site, heavily disturbed by agricultural activities, and a forest reserve with no agriculture. The three species differed in non-breeding spatial strategies, with Willow Warblers having larger home ranges and being non-territorial. Home ranges (kernel density) of the three species were on average 1.5–4 times larger in the disturbed site than in the undisturbed site. Much of the birds’ tree species selection was explained by their preference for tall trees, but all species favoured trees of the genus Acacia. The overall larger home ranges in the disturbed site were presumably caused by the lower density of tall trees. Density of Pied Flycatchers was 24% lower in disturbed habitat (not significantly different from undisturbed) but Willow Warbler density in the disturbed habitat was more than 2.5 times the density in undisturbed. This suggests that the disturbed habitat was less suitable for Pied Flycatcher but not for Willow Warbler. This difference is possibly related to differences in tree species preferences and suggests that at least for some species, presence of preferred tree species is more important than overall tree abundance. Such information is crucial for predicting consequences of habitat changes on larger scales and population levels, as well as for planning potentially migrant-friendly farming practices.
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