Intragroup Behavioral Changes Following Intergroup Conflict in Mountain Gorillas (Gorilla beringei beringei)

Abstract

Group-living animals face a number of threats from extragroup conspecifics: from individuals seeking mating opportunities to rival groups attempting to access limited resources. The consequences of intergroup interactions can therefore include loss of mates, increased energy expenditure, and injury or death. There is increasing evidence that aggressive intergroup interactions can affect subsequent intragroup behavior, and that such post-conflict behavior may be directly related to the threats posed by different opponent groups (e.g., familiar vs. unfamiliar). However, empirical evidence for changes in intragroup behavior following intergroup conflict in social animals is limited. We compared the proximity and behavior of group members before and after 84 aggressive intergroup interactions involving 14 study groups of wild, habituated mountain gorillas (Gorilla beringei beringei) in Volcanoes National Park, Rwanda. Intergroup conflict affected subsequent intragroup behavior in several ways. We found that immediate movement away from the opponent following intergroup conflict was less likely between familiar groups compared to unfamiliar groups. However, both winning and losing groups spent twice as much time moving post-conflict, and losing groups spent less time resting. There was an increase in female intragroup affiliative interactions and a decrease in male intragroup agonistic interactions post-conflict. These results demonstrate that such intergroup contests can influence intragroup dynamics beyond the immediate period of interaction.