Asynchronous hatching and sibling competition in western grebes

Abstract

Observations of western grebe broods during the 3–4 day period of asynchronous hatching revealed brief but intense bouts of pecking occurring between siblings. Feeding experiments conducted on two live-captured pairs and their newly hatched broods showed that older chicks suppressed the responses of their younger siblings to playbacks of the parental food call. Subordinate chicks that emerged from the parent's back feathers and begged simultaneously with their older siblings usually were pecked, and soon refrained from emerging until the older sibling was satiated. Control experiments that involved separating the two chicks and placing one on each of the parents eliminated suppression by the dominant chick. Possibly, asynchronous hatching in grebes provides a means by which parents can create initial asymmetries in the fighting potential of their newly hatched chicks, thereby promoting rapid formation of a self-regulating dominance system among their offspring.