Intergroup encounters in mountain gorillas of bwindi impenetrable National Park, Uganda

The aim of this study was to examine the influence of frugivory and social factors on behaviour during intergroup encounters in the mountain gorillas of Bwindi Impenetrable National Park, Uganda. Frugivory was associated with an increase in the frequency of intergroup encounters, but had no impact on the length of the encounter, or on the type of behaviour exhibited, suggesting that while neighbouring groups may be attracted to limited fruit patches, there was no indication of between group feeding competition. Encounters with solitary males were more likely to elicit more avoidance, less tolerance, more herding behaviour, and a trend towards more aggression than encounters with groups. The number of potential migrant females and the number of silverbacks had no impact on the type of behaviour exhibited. However, an older dominant male was less likely to be aggressive towards the opposing group when a subordinate male was present, suggesting a collective action problem rather than cooperation in multi-male groups. Combined these results suggest that between group competition is linked more to mate defence and acquisition than resource defence. This study contributes to our understanding of the relationship among intergroup encounters, feeding ecology, reproductive strategies and social structure in gorillas.