First tracks of individual Blackcaps suggest a complex migration pattern

Abstract

The Blackcap Sylvia atricapilla is a model species for the evolution of bird migration in a time of global change. However, many assumptions about putative changes to their migratory paths have not been verified because, until recently, it has not been possible to track individual small passerines throughout the entire migration cycle. With the recent development of miniaturised light-level geolocators, it is now possible to track passerines throughout the migration cycle and test these latter assumptions. We deployed 100 geolocators on Blackcaps breeding in southern Germany in 2015, and recaptured three of these birds in 2016. We used a new analytical tool implemented in the R package GeoLight to identify stopover sites during migration. One bird migrated due west to winter in southern England or possibly northwestern France, whereas two birds migrated south towards North Africa via Italy. Although none of the retrieved geolocators collected data throughout the entire migration cycle, the data suggest that migration patterns of the species are more complex than previously thought.