Heterosexual and homosexual behaviour and vocalisations in captive female koalas (Phascolarctos cinereus)

Female koalas (Phascolarctos cinereus) exhibit both homosexual and heterosexual interactions in captivity, even though only heterosexual copulations have been observed in the wild. A key component of sexual interaction is the acoustic bellow, which is produced by males in the wild and both females and males in captivity. We recorded events in both homosexual and heterosexual interactions in a captive koala population, and vocalisations during and outside these interactions. A total of 43 homosexual and 15 heterosexual interactions were recorded in female koalas and were found to have the same principle components following presentation of the mounting male or female to the female: a short delay from neckbite to thrusting, a thrusting phase, followed by a pause and finally jerking behaviour. Thrusting and jerking phases were longest and were of approximately equal length. The delay from neckbite to thrusting, the thrusting phase and the jerking phase were shorter in homosexual than heterosexual mountings, which may relate to the absence of penile intromission and ejaculation. Female koalas exhibited characteristic oestrous and rejection vocalisations that may attract partners or result in them being rejected. The female post-mating calls and calls outside oestrus were longest, followed by female oestrous bellows and male calls, with female rejection calls being the shortest. Rejection calls were higher frequency than the oestrous calls, in particular rejection of a female. Following separation of bellow acoustics into a grunt and a shorter inhalation component, female bellows could be successfully discriminated from male bellows for 64% of the grunt phases, and 71% of the inhalation phases (P < 0.001). Most of the variation between individuals was in the duration, rather than the harmonic range, starting or mean frequency, which were similar for both homosexual and heterosexual copulations. It is concluded that homosexual and heterosexual interactions in female koalas contain the same behavioural components, and similar accompanying vocalisations, although the duration of the different components is specific to the gender and stage of copulation.