Chick Growth, Sibling Rivalry, and Chick Production in American Black Oystercatchers

I studied chick growth, sibling rivalry, and chick production in a population of American Black Oystercatchers (Haematopus bachmani) on Cleland Island, British Columbia from 1975 to 1978. For these birds, survival from hatching until time of first flight is the critical life-history stage. Chick growth varied with brood size, and heavier chicks had higher survival to the time of first flight. Once chicks could fly, however, their survival to 1 and 2 yr of age was not related to brood size or weight at time of first flight. Dominance hierarchies based on weight existed in two-chick broods, and dominant sibs could control access to parental feedings through sibling rivalry. Sibling rivalry probably increases the likelihood of some chick production in years when food is difficult to obtain.