Effect of Photoperiod on the Gonadal Cycle in an Equatorial Bird, Quelea quelea

Abstract

ROWAN'S1 discovery that increasing day-lengths in winter induce reproductive activity and migratory behaviour has been amply confirmed for many species and has contributed greatly to our understanding of the timing of these events in birds of the north temperate zone2. There still remain, however, the problems of regulation of migration in species that winter in the tropics and south temperate zone and regulation of breeding in species that are permanent residents in the tropics. The great dissimilarities in day-length conditions in these zones, and particularly the relative constancy of day-length in the equatorial region, have raised considerable doubt about a possible regulatory function of day-length in equatorial and transequatorial migrants and in tropical species.