Female song in black-capped chickadees (Poecile atricapillus): Acoustic song features that contain individual identity information and sex differences

• Analyzed a large sample of male and female black-capped chickadee songs.
• Used bioacoustical and statistical analyses to classify and compare songs in males and females.
• Found that songs could be sorted based on sex of the singer.
• Males and females produced song that mainly differed on one acoustic feature.
• Future studies will investigate sex perception based on song features.

In temperate songbirds, song has traditionally been considered a vocalization mainly produced by males. However, in many temperate species, it is now recognized that both males and females produce song. The function and structure of male black-capped chickadee (Poecile atricapillus) fee-bee song have been well-studied, but female song, although briefly described in some field reports, has not often been quantitatively examined. We recorded spontaneous fee-bee songs produced by wild-caught male and female adult black-capped chickadees housed in captivity and used bioacoustic analyses to examine seven acoustic features in the songs. Using potential for individual coding and discriminant function analyses, we found that songs were individually distinctive. Using additional discriminant function analyses, we found that songs could be correctly classified based on sex of the producer. Specifically, our results indicate that the frequency decrease within the fee note (i.e., fee glissando) varies between the songs produced by males and females and this suggests that the fee glissando may be used as a sex identifier. While this study provides a quantitative description of the acoustic structure of female song, the development, perception and function of female song in this species requires further examination.