Evidence of an Autonomous Reproductive Rhythm in an Equatorial Bird (Quelea quelea)

Abstract

THAT photoperiod can influence the reproductive and migratory cycles of many species of birds is now well established¹. In male birds the breeding cycle can be resolved into three phases²; the post-nuptial refractory phase during which testes regress and the anterior pituitary becomes unsusceptible to photostimulation; the acceleration or progressive phase when the bird is capable of being stimulated into gametogenetic activity; the final breeding phase. Some workers³ have demonstrated in certain species that all three phases are capable of modification by manipulation of artificial photoperiods and claim that the entire annual cycle is regulated by day-length. But others⁴ place more emphasis on an internal rhythm. In general, the experimental evidence indicates that photoperiods seem to be more influential on the breeding cycles of temperate zone species than on equatorial and desert birds⁵.