Long-term stability of dominance hierarchies in a wild parrot with fission–fusion dynamics

Abstract

Dominance hierarchies are a common feature of stable groups, allowing animals to limit the costs of fighting over access to resources. However, although the emergence of dominance is relatively well known from species that form stable groups, whether hierarchies are maintained in societies with open-group membership remains unknown. One challenge for species that live in an open social environment is that they have the possibility of engaging in dominance interactions with a large number of conspecifics. To better understand the mechanism by which animals navigate the complexities of interacting within a large, open society, we recorded social associations and aggressive interactions in a highly social, communally roosting parrot, namely, the sulphur-crested cockatoo, Cacatua galerita . By following 515 individuals across three neighbouring communities and recording social interactions during foraging, sulphur-crested cockatoos were found to form clear, linear hierarchies. In addition, males ranked higher than females, and adults ranked higher than juveniles. Within sex, where individuals may still have to compete with up to 100 individuals from the same age–sex class, body size did not affect dominance rank. Finally, despite highly dynamic social associations (fission–fusion dynamics) among individuals, hierarchies are stable, with dominance ranks being highly repeatable across at least 3 years. This study shows that closed-group membership is not a prerequisite for stable dominance hierarchies. Show more