Female koalas indulge in lesbian "sex sessions", rejecting male suitors and attempting to mate with each other, sometimes up to five at a time, according to researchers.
The furry, eucalyptus-eating creatures appear to develop this tendency for same-sex liaisons when they are in captivity. In the wild, they remain heterosexual.
Scientists monitoring the marsupials with digital cameras counted three homosexual interactions for every heterosexual one.
"Some females rejected the advances of males that were in their enclosures, only to become willing participants in homosexual encounters immediately after," say the researchers.
"On several occasions more than one pair of females shared the same pole, and multiple females mounted each other simultaneously. At least one multiple encounter involved five female koalas.
"One theory put forward by the researchers is that the females do it to attract males; another is that it is simply hormonal, or that it is a stress reliever.
Scientists from the University of Queensland studied 130 koalas in captivity and will publish their results in the journal Applied Animal Behaviour Science.
"Our aim was to determine the extent of differences in the homosexual and heterosexual behaviour of female koalas and thereby to determine the purpose of female homosexual behaviour in the koala," say the researchers.
"Wild koalas brought into captivity clearly display homosexual behaviour on a regular basis. A total of 15 heterosexual and 43 homosexual interactions were recorded in separate animals. Homosexual behaviour was restricted to females only. Heterosexual encounters were typically twice as long as homosexual encounters," they add.