Seasonality and autonomous reproductive activity in birds

Abstract

A strategy which may be adopted at all latitudes to prepare for seasonal breeding is to use a seasonal variable to phase some form of autonomous reproductive activity into an appropriate relationship with the seasonal change in food supply. In this way the bird is brought into the physiological condition in which nesting can begin, using initial predictive information to exert a phasing rather than a direct inductive action on the reproductive system. Autonomous reproductive activity may be of value to tropical or equatorial species in which seasonal changes in daylength are small; sub-tropical or semi-arid zone species breeding in autumn or winter; temperate zone species which form pair-bonds or establish breeding territories in winter and in migratory temperate zone breeders. Examples are given of autonomous reproductive activity in birds in all of these categories, when maintained for two or more years under constant environmental conditions.