Parental provisioning and predation risk in rhinoceros auklets (<i>Cerorhinca monocerata</i>): effects on nestling growth and fledging

Abstract

We examined the effects of predation risk on the behavior of rhinoceros auklets (Cerorhinca monocerata) breeding at Pine Island, British Columbia, in 1990. Provisioning parents in some areas of the colony risked predation by bald eagles (Haliacetus leucocephalus). Chicks in high and low predation risk areas of the colony hatched on approximately the same date, received similar amounts of food to 46 days of age, grew at the same rate, reached similar peak masses, and fledged at similar masses. However, chicks in high predation areas fledged at a younger age than did chicks in low predation areas. These data are consistent with the hypothesis that parents in high risk areas terminated provisioning several days before those in lower risk areas. Mass at fledging was inversely related to age at fledging in both high and low risk areas. The regression line for the high risk habitats lies below that from the low risk habitats, as predicted by a model that examines optimal time of fledging from the perspective of the parents. We conclude that risk of predation represents a significant cost of reproduction to some rhinoceros auklets and that individual auklets within the colony vary their behavior according to predation risk.