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 birds in many temperate species are thought to sing reduced or quieter songs and appear to sing less often than their male counterparts. Therefore, female song may be easily overlooked. Increasingly, researchers are recording female song in wellstudied species previously assumed to have little or no female song. In this study, we document the extensive use of female song in Orchard Orioles (Icterus spurius), a species with delayed plumage maturation where female song had not been well-documented. Based on observations of females singing in the early breeding season, we hypothesized that female song may function for mate attraction. To formally investigate whether females sing specifically early in the season, we assessed singing rates of each sex throughout the breeding season. We also performed detailed acoustic analyses comparing male and female song structure. Females sang significantly less often than males, and female and male songs were statistically different for five of eight variables investigated, indicating that the two sexes sing acoustically distinct songs. However, females also sang more often than initially assumed, suggesting that researchers may be missing female song in other species if they are not directly searching for it, particularly in species in which yearling males and females have similar coloration. Therefore, this study highlights the need to re-explore well-studied systems. Further research is needed to determine if and how female song may function in this species.RESUMEN. Se piensa que las hembras en las aves de muchas especies de zonas templadas cantan cantos reducidos o mas suaves y aparentemente cantan menos frecuentemente que los machos. Por lo tanto, el canto de las hembras puede ser fácilmente pasado por alto. Cada vez más, los investigadores graban el canto de las hembras en especies muy estudiadas en las que previamente se asumía que las hembras no cantaban o cantaban poco. En este estudio documentamos el uso extensivo del canto de las hembras en Icterus spurius, una especie con maduración tardía del plumaje, donde el canto de las hembras no ha sido bien documentado. Con base en observaciones de las hembras cantando temprano en la temporada de reproducción, hipotetizamos que el canto de las hembras puede utilizarse para la atracción de la pareja. Con el fin de investigar formalmente si las hembras cantan específicamente temprano en la temporada, determinamos las tasas de canto de cada sexo a lo largo de la temporada de reproducción. También realizamos análisis acústicos detallados comparando la estructura del canto de los machos y de las hembras. Las hembras cantaron significativamente menos frecuentemente que los machos y los cantos de las hembras y de los machos fueron significativamente diferentes en cinco de las ocho variables investigadas, indicando que los dos sexos cantan cantos acústicamente diferentes. Sin embargo, las hembras también cantaron más frecuentemente que lo asumido inicialmente, sugiriendo que los investigadores pueden estar pasando por alto el ca...