Convergent vocal strategies of males and females are consistent with a cooperative function of duetting in Australian magpie-larks

Abstract

The relationship between the form and function of coordinated acoustic signals is poorly understood. The coordination of signals by male and female birds to produce duets could be a cooperative display or a consequence of conflict between the sexes. Australian magpie-larks (Grallina cyanoleuca) produce antiphonal duets that function primarily in cooperative territorial defence. I investigate the form of these duets to determine the individual singing strategies of males and females and relate these to what is known about duet function, discussing the implications of variation in the form of duetting among other species. Male and female magpie-larks both initiate duets, and both sexes also frequently sing alone. Though males tend to initiate more vocalisations than females, both are equally likely to join their partners' songs to form duets. Consistent with the cooperative function of their duets, the similarity between the sexes in propensity to duet is maintained when duetting is less likely during the female fertile period, as well as when it is more likely during simulated intrusion. Male and female repertoires are similar, and partners combine their song types non-randomly and with considerable temporal precision to form duets. The interplay between partners that determines duet length and precision is consistent with both sexes benefitting from singing together. The role of duet repertoires and temporal precision in intra- and inter-pair interactions is poorly understood in magpie-larks and other duetting species, and requires further investigation.