Male-male mountings in polyandrous bearded vultures Gypaetus barbatus:: an unusual behaviour in raptors

Male-male mountings appear to be very common in polyandrous bearded vulture Gypaetetus barbatus trios. We observed sexual activity in two trios that occupied the same territory in different years. We recorded a total of 167 copulation attempts. The percentage of male-male mountings recorded was 26.1 and 11.4%, in the period of 1991-1992 and 2000-2001, respectively, with respect to total, homo- and heterosexual matings. We conclude that homosexual interactions do not appear to be directly associated with intrasexual competition (i.e. hierarchical dominance, sperm competition). Rather, our results are more consistent with the idea that this behaviour can regulate the aggression of the males in these groups.