Replacement of breeders and within-group conflict in the cooperatively breeding acorn woodpecker

Abstract

Breeding males or females were removed from groups of the cooperatively breeding acorn woodpecker to study (1) competition among individuals from different groups to fill the breeding vancancies, (2) conflict between parents and offspring within groups over replacement of the removed bird, and (3) conflict between parents and offspring for breeding status. Intense fights (“power struggles”) among nonbreeders from other groups to fill the breeding vacancies developed after the removals. In groups containing only helpers of the opposite sex as the removed bird, replacement was rapid, but in groups containing helpers of the same sex as the removed bird replacement was delayed substantially. In these latter groups parent-offspring conflict developed: helpers could not breed because their parent of the opposite sex was present, and they attacked potential replacements, while their remaining parent advertised for a new mate by calling. Once replacement had occurred, dominance interactions between parents and offspring and among siblings appeared to prevent some individuals from breeding. We conclude that the potential for competition among close kin is high in cooperative species because breeding opportunities are limited.