Social dominance in communal Mexican jays Aphelocoma ultramarina

Social dominance among members of seven social units of communal Mexican jays (Aphelocoma ultramarina) was studied at feeding stations during the non-breeding season. Hierarchies were generally linear. Males were usually dominant to females and there was a tendency for the oldest male in each unit to be the most dominant adult. An unusual pattern of high social status of yearlings was observed. We attribute the high social status of yearlings and adult males to different causes. Adult male dominance is probably related to competition for breeding opportunities within each social unit. We tentatively interpret the dominance of the yearlings in terms of payoff asymmetries and parental facilitation.