Patterns of male reproductive behaviour in multi-male groups of mountain gorillas: examining theories of reproductive skew

The current study examined skew in reproductive behaviour in male mountain gorillas under previously unstudied demographic conditions of large numbers of males. Subjects included 27 males eight to 30 years of age living in three groups in Parc National des Volcans ( Rwanda) between June 2003 and January 2007. Rank was a significant predictor of copulations with both multiparous and nulliparous females, although copulations were more evenly distributed between the three top ranking males than previously reported. Copulations by non-alpha males were unaffected by the level of monopolization potential in the group and relatedness to the alpha silverback. Dispersing males copulated with cycling females prior to their dispersal significantly less than philopatric individuals. As compared to previous studies, we found decreased behavioural reproductive monopolization by the alpha silverback. Additionally, whereas previous studies suggested that patterns of reproductive skew may be best explained by limited control models, our results suggest that concession models should be reconsidered. However, paternity data are needed to determine the relationship between the observed behavioural patterns and changes in reproductive success.