Multiple field study approaches reveal the functions of female song and duets in a temperate songbird

Female song and male–female duetting have been detected mainly in tropical passerines, in which female singing serves a variety of functions that vary with social contexts. Females of numerous temperate passerine species also sing and engage in male–female duetting, but it is still unclear whether these vocalizations function in a similar manner to those of tropical species. To help address this knowledge gap, we used multiple field experimental approaches to investigate the function of female song and male–female duets in a colour-marked population of the plain laughingthrush, Pterorhinus davidi, a socially monogamous, pair-living, resident, temperate species. Baseline observations revealed that both unpaired males and females sing more than paired individuals, and both paired males and females sang more when they were apart, suggesting that females sing to attract potential mates and/or contact their partners. Playback experiments revealed that pair members coordinated their approach to the playback speakers and engaged in duetting, suggesting that duets play a significant role in joint territorial defence. Responses of focal birds to playback stimuli were not sex specific and joint territory defence was male dominated. Mate removal experiments found that both males and females sang more when their mate was experimentally removed, suggesting that females also use songs for contacting a missing mate within their territory. Simulated intrusions using live decoy experiments indicated that duets may also function in shared resource defence during the nonbreeding season. Our study highlights the importance of investigating the functions of female song and male–female duets in songbirds by using a combination of different field approaches to quantify the multifunctional nature of these vocalizations.