Fig. 2

Schematic conceptual framework for the regulation of nocturnal departure time in songbird migrants. The innate program provides the circannual, circadian rhythms and spatiotemporal schedule of migration. The photoperiod is used to calibrate or reset the innate migration program. The seasonal variation in birds’ fuel load and the seasonal-specific sequence of molt are regulated among other traits by the innate rhythms (broken arrows). The realized nocturnal departure time represents the interplay of both the intrinsic and extrinsic factors modulating the endogenous stimuli