Female Dark-eyed Juncos (Junco hyemalis thurberi) produce male-like song in a territorial context during the early breeding season

Reports of female song, once considered a rarity, have recently increased across a variety of avian taxa. Females of many species can be induced to produce male-like song with exogenous testosterone, but observations of female song in free-living birds remain limited by incomplete sampling of females. Here, we report three independent observations of female dark-eyed juncos (Junco hyemalis) producing male-like song early in the breeding season (i.e. post-territory establishment, pre-nesting) in a recently established non-migratory, urban population. To elicit song, we presented 17 free-living junco pairs with a live, caged female conspecific. Three unique females responded to our trials by diving at the intruding female, chasing their (male) mate, fanning their tail feathers, and singing a trilled song similar in structure to male long-range (broadcast) song. We compared male and female songs quantitatively and found that the two sexes were statistically similar in many spectral and tem...