Male mating patterns in wild multimale mountain gorilla groups

Although mountain gorillas, Gorilla gorilla beringei, are classified as having a one-male mating system, approximately 40% of the social units are multimale groups. I observed two multimale groups of mountain gorillas at the Karisoke Research Center, Rwanda, Africa, for 17 months to determine male mating patterns and male-male mating harassment in relation to both male dominance rank and female reproductive status. Dominant males mated significantly more than did individual subordinate males, and dominant males mated more with cycling adult and pregnant females. The dominant males participated in 47 and 83% of observed matings in the two groups. Subordinate males were more likely than dominant males to mate with subadult females. Eleven of 14 females were observed to mate with more than one male, and multiple males mated with three of the five females observed at the probable time of conception. Mating harassment was initiated and received by both dominant and subordinate males. Mating harassment occurred infrequently (during 30 and 22% of matings in each group), usually consisted of mild aggression, and usually terminated copulations by subordinate males, but not those by dominant males. These results suggest that multimale mountain gorilla groups can be favourable environments for subordinate males to obtain mating opportunities. Dominant males may be unable or unwilling to prevent subordinate males from mating. Based on behavioural observations, mountain gorillas can have a multimale mating system but further research on the role of females in male mating success and paternity determination is needed to understand fully this species' mating system. Copyright 1999 The Association for the Study of Animal Behaviour.