Determinants of social rank in female black-capped chickadees (Poecile atricapilla)

Abstract

Black-capped chickadees (Poecile atricapilla) mate assortatively by social rank. Previous field studies suggest that intrinsic characteristics of females may influence success at pairing with dominant males. Here we examined factors leading to dominance using dyads of captive unfamiliar females. The owner–intruder hypothesis predicts that prior residency determines dominant–subordinate relationships. The resource-value hypothesis suggests that social status is initially determined by need and the relationship persists through familiarity of the interactants. The resource holding potential hypothesis suggests that individuals win in dyadic contests because of intrinsic characteristics such as size or age. We tested the owner–intruder and resource-value hypotheses by allowing females prior residency in aviaries where dominance interactions subsequently occurred and by food depriving the intruders. Post-hoc comparisons of dominant–subordinate attributes tested the resource holding potential hypothesis. We found that owners were more likely to win interactions. Hungry individuals showed no competitive advantage. Dominants and subordinates did not differ in morphology or age. Our results agree with data from willow tits (Parus montanus) which show that captive females establish dominance independent of males and that prior residence plays a key role. These findings, together with field studies, suggest that assortative mating in chickadees results, at least in part, from intrasexual interactions among females.