Spatial behavior and habitat use in widely separated breeding and wintering distributions across three species of long-distance migrant Phylloscopus warblers.

AIM: To investigate the ecological relationship between breeding and wintering in specialist and generalist long-distance migratory species, and the links between densities and range sizes. LOCATION: Denmark, Senegal and Ghana. METHODS: We use radio tracking to study spatial behavior and habitat use in three morphologically and ecologically similar and closely related Phylloscopus species on their widely separated breeding and wintering distributions. During wintering and breeding, willow warblers P. trochilus (winter: n = 9, breeding: n = 13), chiffchaffs P. collybita (n = 11, n = 7), and wood warblers P. sibilatrix (n = 17, n = 14) were tracked. RESULTS: Willow warblers P. trochilus increased home range sizes in winter, whereas it was similar in chiffchaffs P. collybita and wood warblers P. sibilatrix, in both seasons. Home ranges overlapped more in winter than in the breeding season. In winter, home range overlap was similar among species but larger overlap during breeding was indicated for willow warblers. Tree cover was unrelated to home range size but significantly higher in breeding than in winter in all species. However, whereas willow warblers and wood warblers maintained some degree of tall tree cover inside their home ranges in winter, chiffchaffs changed from more than 80% to <1% tree cover, indicating a niche shift. MAIN CONCLUSIONS: Individuals of all three species showed changes between breeding and wintering areas in spatial behavior and habitat availability, with larger overlap in winter. The differences in patterns were potentially related to being generalist (willow warbler) or specialist (chiffchaff and wood warbler). These ecological relationships are important for the conservation of migrants and for understanding the link between breeding and wintering distributions and ecology.

Early returning long-distance migrant males do pay a survival cost.

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.

No apparent gain from continuing migration for more than 3000 kilometres: willow warblers breeding in Denmark winter across the entire northern Savannah as revealed by geolocators.

BACKGROUND: For 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). RESULTS: Birds 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. CONCLUSION: The 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.