Large female song repertoires and within‐pair song type sharing in a temperate breeding songbird

Female song has been significantly understudied in songbirds. While male song has been studied for centuries, female song has only begun to be explored in the last few decades. This is especially true in relation to understanding repertoire size and function. In male songbirds, song repertoires are thought to function primarily in mate attraction and territory defense. Only a few studies to date have explored repertoire size in female songbirds, and many of those focused on tropical duetting species. We quantified the size and explored the function of song repertoires in a temperate breeding songbird, the eastern bluebird. Female song in eastern bluebirds functions primarily in communication with a social mate in order to maintain long‐term pair bonds. Previous work in this species also documented that males have large repertoires serving a variety of purposes. We found that female bluebirds have similar song repertoire sizes to males. Also, females share their repertoires and song types more closely with their mate than shared with non‐mates. This is one of the first studies to document large female repertoires in a non‐duetting temperate species. Our findings indicate that large female repertoires and song type sharing in this species is integral to communication between social mates. Additionally, the large effect size of song type sharing with newly formed mates suggests open‐ended learning may be present in this songbird, a previously under‐documented phenomenon in females. This study provides the groundwork to explore the ontogeny and evolution of song repertoire size in female songbirds and to expand our understanding of song repertoires beyond their functions in males as an indicator of male fitness. Female song repertoires are understudied and not well understood. We found that female eastern bluebirds have large repertoire sizes similar to male repertoires in this species. Additionally, we found significant song type sharing between mates suggesting that female repertoires function for within‐pair communication.