Disentangling the effects of timing and parental quality on the breeding success of a seabird: an experimental approach

SVAGELJ, W. S.; QUINTANA, F.

Perth, Western Australia

Congreso; 13th International Behavioral Ecology Congress; 2010

International Society for Behavioral Ecology

Avian breeding success usually declines over the course of the season, which may be a direct effect of breeding time (by a seasonal reduction in food supply), an effect of parental quality (young or less-capable individuals breeding late), or a combination of the two. To understand the fitness consequences of the seasonal decline in breeding success requires distinguishing between these two effects. Using a cross-fostering protocol, we evaluated the relative importance of timing and parental quality on the reproductive performance of the Imperial Shag (Phalacrocorax atriceps). We extended or reduced the incubation period by exchanging entire clutches between early and late breeders. High (old) and low (young) quality pairs thus reared their chicks at the same time both early and late in the season. We found that both high and low-quality pairs raised more chicks early in the season. Reproductive performance of high quality pairs was consistently better than low quality pairs breeding at the same time. While breeding-failure probability did not differ between early and late breeders, low-quality pairs failed more than high-quality pairs. Our results showed that both timing of breeding and parental quality affected the breeding success of the shags, being, the latter, the main affecting factor.