A comparison of migratory strategies of partial migratory raptors from Germany

Abstract

The phenomenon of partial migration in birds in which some individuals of a population are migratory while others stay in the breeding area is of increasing scientific interest. The strategies of partial migratory raptors from Central Europe are, however, unclear for most species. We analysed ring re-encounter data of Eurasian Sparrowhawks Accipter nisus and Common Buzzards Buteo buteo ringed in Germany in terms of distances and directions between ringing and re-encounter sites. We investigated possible differences between sexes (only in Sparrowhawks) and age classes, as well as effects of ringing region, seasonal weather (in the form of North Atlantic Oscillation indices) and long-term temporal changes (including climate change) on migratory strategies by means of generalized linear models. We found that, in both species, migration is mostly conducted by juveniles, although migratory adults were also found. In general, male Sparrowhawks tend to migrate less than females. Sparrowhawks from different regions showed no differences in migration activity and no responses to long-term temporal changes. They did not respond to seasonal weather either. Buzzards showed strong responses to winter weather (‘winter escapes’) predominantly in highland regions, and a reduction of migratory intensity probably due to global warming. We compared our results to ones for Common Kestrels Falco tinnunculus and found most similarities between Kestrels and Sparrowhawks.