DOES BREEDING EXPERIENCE EXPLAIN INCREASED REPRODUCTIVE SUCCESS WITH AGE - AN EXPERIMENT

Accumulation of breeding experience is often assumed to explain enhanc ed reproductive performance with age. This hypothesis is usually teste d by comparing reproductive performance of individuals of the same age but having different amounts of previous breeding experience, thus us ing natural variation in the age of first breeding. However, individua l quality may confound such a comparison, since ape of first breeding is likely to covary with individual quality. I delayed experimentally the age of first breeding in female collared flycatchers Ficedula albi collis, and found that: (i) individual quality differences were likely to cause the observed higher reproductive success of unmanipulated ex perienced as compared with inexperienced two-year-old females; and (ii ) breeding experience had no or very little effect on reproductive per formance as compared with the effects of reproductive costs. A review of previous tests of the breeding experience hypothesis in birds revea ls no consistent trends, although some studies suggest that breeding e xperience may improve reproductive performance. However, several of th ese studies also suggest that high-quality individuals start to breed at a younger age. Hence, at present there is no unequivocal evidence t hat breeding experience explains the enhanced reproductive performance with age. It is more likely that other age-related improvements in co mpetence (e.g. foraging, nest site selection) and increased reproducti ve effort with age are responsible for this change.