Territorial defence is the major function of female song in the superb fairy-wren, Malurus cyaneus

Abstract

Unlike most passerines, female superb fairy-wrens are prolific solo singers. Four hypotheses for the function of female song were evaluated: (1) to defend territories; (2) to maintain contact with mates; (3) to assess the amount of time mates are spending on the territory; and (4) to solicit displays from extra-group males. Female song rates increased as fairy-wrens reasserted territorial boundaries after a period of communal winter flocking. Song rates were not affected by the age of the female, the time she had been paired to her current mate, the time her mate had been the dominant male on the territory, or the composition of her group. However, females that had recently established territories, or had undergone significant changes in territorial borders, sang at higher rates than females that had been established in their territories for many years. Playback experiments revealed that: (1) females were more likely to sing in response to songs of male or female neighbours than to songs of their mates or their own song; (2) females responded more intensely to songs of female strangers than to songs of female neighbours; (3) extra-group males did not respond with extra-group courtship displays when a female's song was played back from her territory, although some territorial responses were elicited. The stronger response to neighbours indicates that mate location and mate assessment are not major functions of female song. The display solicitation hypothesis can be rejected because extra-group males did not respond to playbacks of females, and there was no correlation between female song rate and the incidence of male display. In contrast, the results suggest that the major function of female song is territorial defence, and that receivers use variation in the song to discriminate between different classes of individuals (self, mate, neighbour, stranger).