Captive female Koala's are bisexual

Queensland Koala (Phascolarctos cinereus adustus)
Diet: Eats about one pound of leaves a day (from both eucalyptus and non-eucalyptus trees)
Habitat: Eucalyptus forests in Australia
Reproduction: Breeding season is between October and February, males mate with several females, gestation lasts 34 to 36 days after which a single koala baby is born, the 2 ounce baby stays in it's mothers pouch for another 7 months.
Notes: Sleep about 18 hours a day, males are up to 50% larger than females and have broader faces
Homosexuality has been observed in many classes of vertebrates. Interestingly, a study by Feige et. al (2007) found that female koalas exhibit both heterosexual and homosexual behaviors in captivity. However, in the wild only heterosexual mating has been observed. Homosexuality in solitary mammals, like the koala, is usually only seen under two conditions: one, limited numbers of a certain sex dictates the need for reproductive success through homosexuality; and two, when kept in captivity, homosexuality is used to relieve stress and exhibit dominance. In the wild, male koalas make a loud acoustic bellow to attract mates or defend their territory from other males. Female bellows have not been recorded in the wild. In captivity, this bellowing sound is made by both males and females. In captivity, female bellows may be used to alert males when she is ready to mate, or to warn males when she is not ready to mate. In this study, a total of 43 homosexual and 15 heterosexual interactions and were made by females. Copulation behavior with other females is very similar to the behavior exhibited by heterosexual mating. One factor to consider in this study is females were housed in single-sex enclosures, where more than one female may be ready to mate and competition for males is high. Studies have found that homosexual behavior in koala's is not spontaneous, but is usually in response to the presence of a male. However, homosexual behavior is not used to attract a male, because males are not drawn to homosexually engaged females. Some females in this study rejected the males only to begin mating behaviors with other females. This is not unique to Koalas, and seems to be in response to increased stress or increased frequency of sexual encounters. Another study reported that homosexual interactions made up 11% of the interactions of captive female koalas, and is most likely due to the skewed sex ratio among the captive population. "It is likely, therefore, that rather than having adaptive significance which is unlikely in a short-lived captive population, the homosexual behaviour observed is an expression of a hard-wired behavior that is stimulated in the hypothalamus in the presence of elevated oestradiol concentrations." It seems that homosexual activity may serve as a stress release for captive female koalas.



Sources:
Feige, S., Nilsson, K., Phillips, C. J., , & Johnston, S. D. (2007). Heterosexual and homosexual behaviour and vocalisations in captive female koalas Phascolarctos cinereus. Applied Animal Behaviour Science, 103(1-2), 131-145. doi:10.1016/j.applanim.2006.03.014
http://www.thebigzoo.com/Animals/Queensland_Koala.asp
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