Social interactions in gorillas

Male – male social interactions in breeder and bachelor groups of gorillas (Gorilla gorilla): an indication of behavioural flexibility

A multi-institutional design for observations of male gorillas in six breeder and five bachelor groups was validated by calculating behavioural diversity, confirming that known behavioural phenomena, e.g. the effect of age, could be determined across groups.

There was a significant effect of age ((F(1,38) = 81.665, p < 0.000), with younger animals exhibiting greater behavioural diversity. Alternative behavioural phenomena were then investigated to compare male social interactions in breeder and bachelor groups.

Bachelor groups consistently exhibited further distances between themselves and their first and second nearest neighbours (F(1,26) = 37.434, p <0.000; F(1,30) = 119.814, p < 0.000 respectively), significantly lower frequencies of aggressive interactions than breeder males (F(1, 30) = 21.145, p < 0.000), and a significantly reduced Relationship Quality Index (F(1, 26) = 5.099, p = 0.033) indicating that bachelor males exhibit fewer affiliative interactions than dominance interactions. These results suggest that bachelor males exhibit avoidance strategies rather than risk aggression, and that captive bachelor groups are less strongly bonded than captive breeder groups, a finding consistent with the suggestion of wild western bachelor gorilla groups being unstable (Levrero et al, 2006).

Bachelor groups have been suggested to be a suitable environment for gorillas to learn social interactions (Levrero et al, 2006; Robbins, 1999), however the reduced expression of affiliative behaviours in captive bachelor groups may indicate a lack of opportunity to learn affiliative social behaviours, and reinforces the need to assess the social competence of captive bachelor males as they move into new social groups (breeder or bachelor).