This is the third in a series of articles on avian reproduction. The first two articles addressed The Incredible Female Bird Reproductive System and The Male Bird Reproductive System . This article discusses some of the factors which trigger and stimulate reproduction and as well as some of the resulting hormonal and reproductive system changes. Some birds, such as chickens, are continuous breeders , reproducing throughout the year. Other birds such as parrots are opportunisitic breeders , breeding during certain cycles or when favorable conditions exist.
Spring heralds the onset of reproduction in many avian species.
Reproduction occurs most successfully when the environmental conditions are favorable for the survival of offspring and food is plentiful. Day length or photoperiod plays an important role in birds that are seasonal reproducers. Environmental light stimulates neural receptors which, in conjunction with an internal circadian cycle, enables the bird to respond to the most favorable time for reproduction. As day length increases in the winter and spring, the ovaries and testes of most temperate species increase in size and undergo development. In addition to day length, temperature and humidity influence reproduction in many free ranging species.