Divorcing a current partner to re-pair with a mate of higher quality may be a strategy to increase reproductive success used by socially monogamous birds. By increasing the availability of males through selective mate removal during the nest building period, we found that female black-capped chickadees, Parus atricapillus, will desert their mates to pair with males of higher social rank, a trait closely associated with resource holding potential in this species. Females from neighbouring territories were more likely to desert their mates for high ranked rather than the low ranked widower males; six of seven high ranking and one of six low ranking males were chosen by the divorcing females. Six of the seven widower males chosen by divorcing females were dominant to the males that the females deserted. Once released, the originally removed females were able to re-establish pairbonds with their mates. Higher social ranks of removed females may have enabled them to exclude lower ranked replacement females, and may reflect a natural constraint on female choice.
Bird flocks were assessed for hierarchies, selective mate removal