We present evidence from experiments on overwintering populations of two Palearctic-Indian latitudinal migratory birds, the black-headed bunting (Emberiza melanocephala) and the red-headed bunting (E. bruniceps), that the bird’s clock in interaction with day length regulates seasonal rhythms of migration and reproduction such that physiological conflict between them is reduced. Initiation and termination of the body mass and testicular cycles are separately regulated photoperiodic events. For example, under stimulatory photoperiods the response curve of body mass does not overlap with that of the testicular growth. A response-specific photoperiodism is adaptive, since gain in body mass, critical to spring migration, precedes gonadal recrudescence. Finally, migration as indicated by the night-time migratory restlessness under experimental situations (e.g., intense locomotion under caged condition-called Zugunruhe) appears to be regulated by a separate circadian oscillator.