Abstract

Black-capped (Poecile atricapillus) and Carolina ( P. carolinensis) chickadees hybridize extensively in a long and narrow contact zone, but mechanisms of mate choice remain incompletely understood. I investigated nonbreeding social relationships, which may affect pairing, in southeastern Pennsylvania. During my study, irrupting Black-capped Chickadees joined local hybrid residents, so I also investigated their relationships. Males participated in more social interactions than did females, but there was no difference in average dominance rank. Older birds were not more dominant than younger birds. Known social pairs did not have high association index values during the winter months. Sex or dominance rank did not affect distance moved between breeding season and winter months. Irruption Black-capped Chickadees did not become integrated within local hybrid flocks. This study suggests that flock structure in local flocks maybe less tightly structured and more difficult to study than in regions where relationships among Black-capped Chickadees have been investigated.