||Asymmetries in mate choice or fitness can cause hybrid zones to move. The northward-shifting contact zone between Black-capped and Carolina chickadees ( Poecile atricapillus and P. carolinensis ) represents a rare documented example. Among hybrid zone chickadees, some but not all males produce songs of both species. I investigated song repertoires in relation to extra-pair paternity in southeastern Pennsylvania in 2005-2007. Both songs and mixed song (combining notes of the species) persisted, but Carolina songs increased proportionately by 11% since 2001 while black-capped songs declined by 17%. Most males (73%) were bilingual, as in 2001. Extra-pair matings accounted for 42% of offspring, occurring in 74% of broods. Male repertoire type did not influence patterns of extra-pair parentage, although yearling males lost paternity more than did older males. The failure of song to influence extra-pair paternity does not negate a possible role in hybrid mating, but other mechanisms may favor Carolina genotypes.