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.曾被视为罕见现象的雌性鸣唱报道，近年来在各类鸟类类群中均有所增加。诸多鸟类物种的雌性个体可通过外源性睾酮诱导出类似雄性的鸣唱，但对野生鸟类雌性鸣唱的观测仍因雌性采样不充分而受限。本研究针对一个新近建立的非迁徙性城市种群，报道了三例独立观测到的雌性暗眼灯草鹀（dark-eyed junco，Junco hyemalis）在繁殖季早期（即领地建立后、筑巢前）发出类似雄性的鸣唱的案例。为诱导鸣唱行为，我们向17对野生灯草鹀配偶展示了一只活体笼养的同种雌性个体。共有3只独特的雌性个体对实验刺激做出反应：它们冲向入侵雌性、追逐其（雄性）配偶、展开尾羽，并发出结构与雄性长距离（广播式）鸣唱相似的颤鸣鸣唱。我们对雌雄鸣唱进行了定量比较，结果显示两性在诸多频谱与时域特征上无显著差异，但雌性鸣唱的最低频率与峰值频率均显著低于雄性。这一结果尤为出人意料，因为已知该城市种群的雄性鸣唱最低频率显著高于附近山地种群的雄性个体。观测到雌性鸣唱的季节与社会情境均提示，雌性鸣唱可能具备配偶守卫与防范多配性的功能，但仍需更多数据来验证这一假说。雌性鸣唱是否普遍存在于所有暗眼灯草鹀的繁殖季早期，还是仅局限于该特定的城市非迁徙种群，仍是未来研究亟待解答的重要科学问题。