Social decision-making in a wild parrot relies on both individual recognition and intrinsic markers

Dominance hierarchies allow group-living animals to limit the potential costs of fighting over access to resources, but can these be maintained in more open, fission-fusion societies, where individuals have incomplete social information? We recorded social associations and aggressive interactions in a highly social, large-brained parrot, the sulphur-crested cockatoo (Cacatua galerita) . By following 411 individuals across three neighbouring roosts, we show that sulphur-crested cockatoos form shallow, but stable, hierarchies that incorporate birds from within and outside the roost. We find that hierarchies are maintained via a two-fold strategy when initiating or reacting to an aggression: initiate and escalate interactions based on rank difference when familiar, and direct and escalate interactions based on weight similarity when unfamiliar. Our results demonstrate the association between complex cognition, social memory, and the maintenance of dominance hierarchies in fission-fusion systems. ### Competing Interest Statement The authors have declared no competing interest.