Does breeding experience explain increased reproductive success with age? An experiment

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Abstract
Accumulation of breeding experience is often assumed to explain enhanced reproductive performance with age. This hypothesis is usually tested by comparing reproductive performance of individuals of the same age but having different amounts of previous breeding experience, thus using natural variation in the age of first breeding. However, individual quality may confound such a comparison, since age of first breeding is likely to covary with individual quality. I delayed experimentally the age of first breeding in female collared flycatchers Ficedula albicollis, and found that: (i) individual quality differences were likely to cause the observed higher reproductive success of unmanipulated experienced as compared with inexperienced two-year-old females; and (ii) breeding experience had no or very little effect on reproductive performance as compared with the effects of reproductive costs. A review of previous tests of the breeding experience hypothesis in birds reveals no consistent trends, although some studies suggest that breeding experience may improve reproductive performance. However, several of these studies also suggest that high-quality individuals start to breed at a younger age. Hence, at present there is no unequivocal evidence that breeding experience explains the enhanced reproductive performance with age. It is more likely that other age-related improvements in competence (e.g. foraging, nest site selection) and increased reproductive effort with age are responsible for this change.