Birds sing to defend territories and attract mates — a male bird singing from a fencepost is simultaneously warning rival males to stay away and advertising his quality to any female within earshot. Birds also vocalize to coordinate with their pair partner, maintain social bonds within flocks, and signal individual identity to neighbors. In duetting species like Carolina Wrens, mated pairs weave their voices together in precisely timed performances that reinforce the pair bond and allow coordinated territory defense. While most research has focused on male birdsong, more work is being done to better understand when and why female birds sing.
Recently published research sheds light on traits shared among species where female singing is more prevalent. In one study, an analysis of ecological and natural history traits for 1,300 songbird species showed that female song is far more common than previously appreciated, and that its incidence is most directly predicted by year-round territoriality, biparental care, and large body size. In other words, when the birds don’t migrate and both sexes defend a territory and raise young, females may sing to compete for high-quality mates. Another study of 1,000 songbird species added to these findings, determining that cooperative breeding coevolved with female song, which may help with social cohesion.