Data from: 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
temporal characteristics, but female songs had significantly lower minimum
and peak frequencies than males. This result is particularly surprising,
as males in this urban population are known to sing at a significantly
higher minimum frequency than males in a nearby montane population. Both
the seasonal and social context in which these songs were observed suggest
a potential function for female song in mate guarding and polygyny
prevention, but more data are needed to test this hypothesis. Whether
female song is common in all dark-eyed juncos during the early breeding
season or if it is restricted to this particular urban and non-migratory
population remains an important question for future research.