Female song is structurally different from male song in Orchard Orioles, a temperate-breeding songbird with delayed plumage maturation

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 well-studied 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.