AGE AND REPRODUCTION IN BIRDS - HYPOTHESES AND TESTS

It is well known that reproductive performance improves with age in bi rds. Many hypotheses, involving factors such as differential survival, delayed breeding, breeding experience, foraging ability and reproduct ive effort, have been proposed to explain this pattern. Although these hypotheses are not mutually exclusive, they can be classified in thre e major groups relating to progressive appearance or disappearance of phenotypes, age-related improvements of competence, and optimization o f reproductive effort. However, a closer examination of the literature reveals that only few studies have rigorously tested the hypotheses. Future work should focus on carefully designed tests that critically i nvestigate the hypotheses.