Eurasian blackcaps (Sylvia atricapilla) are common breeding birds across Europe, and exhibit a remarkably broad spectrum of behavioural variation in migratory status and orientation direction. Phenotypic variation across populations ranges from residents to short-, medium- and long-distance migrants. In addition, migrants exhibit variation in migratory orientation strategies and form so-called migratory divides, i.e. areas where neighbouring populations breeding in close proximity have distinct migratory routes and non-breeding grounds. Blackcaps are distributed continuously across the central European migratory divide, with breeding populations in Europe and overwintering areas in southern Iberia and northern Africa. In autumn, populations breeding west of the divide migrate southwest (SW) around the Mediterranean Sea, while populations east of the divide migrate southeasterly (SE). In addition, since the 1960s, a growing number of birds breeding in central Europe migrate northwest in autumn to overwinter in the British Isles, possibly because of the milder wintering conditions.

We use ringing recovery analyses to characterise general patterns of migratory variability in a spatiotemporal context, and characterise individual migratory behaviour in the wild using light-level geolocator technology, as well as carefully controlled behavioural observations in the lab.