Female and male song rates across breeding stage: testing for sexual and nonsexual functions of female song

As a textbook example of a sexually selected trait, song in male birds has been extensively examined in the context of female mate choice and male-male competition for access to mates. Female song is also phylogenetically widespread, and probably ancestral. However, we know relatively little about when and why females sing. Female song may be important for female-male communication, e.g. fertility advertisement, mate attraction or coordinating the care of young. Alternatively, female song may function in the context of female-female competition for reproductive resources, e.g. nest sites, year-round territories or parental assistance. We quantified spontaneous song, and song in response to playback of an unfamiliar female song, in female and male superb fairy-wrens, Malurus cyaneus, across breeding stages. We found that females and males sang with roughly equal frequency spontaneously; however, females sang much more frequently than males in response to playback of unfamiliar female song. We found no difference in song rates across breeding stage, and no effect of age or the presence of subordinates. In both sexes, song rates increased slightly across the breeding season. Female song rates were also repeatable across the season. Overall, the results suggest that although female song is likely to be a multipurpose trait, as in males, the primary function in superb fairy-wrens appears to be female-female competition.