Heterosexual and homosexual behaviour and vocalisations in captive female koalas (Phascolarctos cinereus)
Feige, S, Nilsson, K, Phillips, CJC & Johnston, SD 2007. Applied Animal Behaviour Science, vol. 103, no. 1, pp 131-145.
Female koalas in captive environments engage in both homosexual and heterosexual interactions, although only heterosexual interactions have been recorded in nature. In captivity, female koalas also produce acoustic bellows, a sexual behaviour typically only observed in males. This study of koalas in Lone Pine Koala Sanctuary revealed that homosexual interactions between females comprised the same component behaviours and vocalisations as, but were shorter in duration than, heterosexual interactions.
A typical heterosexual interaction between koalas comprises the following stages: mounting, neckbite, a pause, thrusting, a second pause, jerking, and disengagement. In this study, the same stages were fulfilled in homosexual interactions between two or more female koalas. In homosexual interactions, however, the first pause, thrusting and jerking stages were shorter in duration than in heterosexual interactions because penile intromission and ejaculation did not occur. Regarding sexual vocalisations, females exhibited both oestrus calls to attract mates as well as rejection calls. Rejection vocalisations were of a greater range and frequency than oestrus vocalisations, especially when the rejected partner was also female.
For a solitary and largely sedentary species like the koala, acoustic communication via vocalisations is critical for the expression of sexual behaviours. It is important that female koalas are able to advertise their oestrus state vocally to attract a mating partner. Interestingly, however, the greater harmonic range and frequency of rejection calls than oestrus bellows observed in this study suggests that it may be even more important for females to express their rejection of copulation attempts, potentially due to the risk of danger and indication of subordinacy for the mounted female. Competition for male attention may also be a factor influencing the sexual vocalisations of female koalas in captivity, as the ability to produce the loudest or deepest bellow may indicate a female’s superiority among other females that may also be in oestrus.
Homosexual behaviour among koalas is unique to females in captivity. Though several possible explanations for these interactions exist, the most likely function of homosexual interactions among female koalas is stress release during oestrus when heterosexual interactions cannot be fulfilled. These findings enhance our understanding of the sexual behaviours of koalas as well as the management of captive koalas in single-sex environments.
Summarised by Joanna Horsfall
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