Investigating connectivity and seasonal differences in wind assistance in the migration of Common Sandpipers

Many migratory bird species have undergone recent population declines, but there is considerable variation in trends between species and between populations employing different migratory routes. Understanding species-specific migratory behaviours is therefore of critical importance for their conservation. The Common Sandpiper Actitis hypoleucos is an Afro-Palaearctic migratory bird species whose European populations are in decline. We fitted geolocators to individuals breeding in England or wintering in Senegal to determine their migration routes and breeding or non-breeding locations. We used these geolocator data in combination with previously published data from Scottish breeding birds to determine the distributions and migratory connectivity of breeding (English and Scottish) and wintering (Senegalese) populations of the Common Sandpiper, and used simulated random migrations to investigate wind assistance during autumn and spring migration. We revealed that the Common Sandpipers tagged in England spent the winter in West Africa, and that at least some birds wintering in Senegal bred in Scandinavia; this provides insights into the links between European breeding populations and their wintering grounds. Furthermore, birds tagged in England, Scotland and Senegal overlapped considerably in their migration routes and wintering locations, meaning that local breeding populations could be buffered against habitat change, but susceptible to large-scale environmental changes. These findings also suggest that contrasting population trends in England and Scotland are unlikely to be the result of population-specific migration routes and wintering regions. Finally, we found that birds used wind to facilitate their migration in autumn, but less so in spring, when the wind costs associated with their migrations were higher than expected at random. This was despite the wind costs of simulated migrations being significantly lower in spring than in autumn. Indeed, theory suggests that individuals are under greater time pressures in spring than in autumn because of the time constraints associated with reproduction.