Regulation of provisioning rate in the Thick-billed Murre (Uria lomvia)

Abstract

Many studies of marine birds report that parents regulate provisioning, thus meeting their offsprings’ nutritional requirements at minimum cost. Others report that food availability limits provisioning, mediated by parental body condition. One hypothesis that might explain these discrepancies holds that seabirds are better able to regulate provisioning under more favourable feeding conditions. To test this, we studied provisioning behaviour in the Thick-billed Murre (Uria lomvia L., 1758) in three colony-years that, based on chick growth rates, spanned a wide range of feeding conditions. We considered that parents regulating provisioning would (i) deliver more food as their offspring aged, to meet their increasing requirements, (ii) space consecutive deliveries nonrandomly in time, and (iii) maintain additional mass to buffer against future deterioration in feeding conditions. As predicted, we found that (i) provisioning rates increased with chick age in all three colony-years, but more strongly when feeding conditions were better; (ii) consecutive deliveries were spaced nonrandomly in all three colony-years, again more strongly when feeding conditions were better; and (iii) adults were heavier at mid chick-rearing when feeding conditions were better. Future studies that investigate how feeding conditions influence seabird provisioning could improve our understanding of how long-lived species optimize reproductive effort in variable environments.