Experimential evidence for endogenously programmed differential migration in the blackcap (Sylvia atricapilla)

Female hand-raised blackcaps (Sylvia atricapilla) held in constant conditions (except for simulated seasonal changes in photoperiod) showed significantly more, and significantly longer, autumnal migratory activity as well as significantly later initiation of spring migratory activity than males from the same population (including siblings) held under identical conditions.This research was supported by the Alexander von Humboldt Foundation (Terrill) and the Deutsche Forschungsgemeinschaft (Berthold).