Contributions to care vary with age, sex, breeding status and group size in the cooperatively breeding apostlebird

Abstract

Investment strategies in cooperative societies are often complex but should reflect individual variation in the costs and benefits of providing care. We examined the contributions to incubation and nestling provisioning by individual members of 16 groups of the cooperatively breeding apostlebird, Struthidea cinerea. Contributions varied in relation to the age, sex and breeding status of the carer, and with group size. Yearlings were less likely to help than older birds, and, when they did, spent less time incubating and fed the brood less often. Among adults (≥2 years old), male helpers incubated less than breeders or female helpers. Mothers spent more time incubating than female helpers, an..