Given that neither the simpler alternative that in all male groups such fellatio may represent misdirected sexual behavior, nor the two previously proposed functional hypotheses were supported by the data, I propose another functional hypothesis. As such, male-male fellatio can be considered as homosexual behavior, two functional explanations could account for this behavior the social bonding and the social tension regulation hypotheses suggested in a previous review. Unassociated with allogrooming, same-sex genital licking occurred among males in the all male clusters. The female clusters may also contain a few males. During the mating season, adult flying foxes roost in same-sex groups, forming ball-shaped clusters which provide warmth. In the present paper, a form of fellatio in wild Bonin flying foxes, Pteropus pselaphon, performed between adult males has been reported. A recent focus of interest has been on the functional significance of genital licking (fellatio and cunnilingus) in relation to sexual selection in Pteropodid bats.