Chimpanzee immigration: complex social strategies differ between zoo-based and wild animals

Chimpanzee inter-group encounters are typically aggressive in nature, as individuals have evolved the predisposition to jointly defend their home range against neighbouring groups. In the current study, we present data on the behavioural strategies of chimpanzees (Pan troglodytes) during the integration of one male and two female into a well-established group at Basel Zoo, Switzerland. We found that, shortly after integration, social relationships were generally of better quality in dyads of individuals from the same group than dyads of individuals from different origins. More interestingly, immigrants targeted males as preferred interaction partners, contrary to what is seen in inter-group encounters in the wild. In addition, immigrants also targeted the resident juveniles for play interactions, significantly more so than residents did. The alpha male’s policing of his resident group members further facilitated immigrants’ integration, including the integration of another male. In contrast, both resident and immigrant females had better relationships with members from their own group than with members from other groups. Overall, these diverse behavioural strategies led to the successful long-term integration of the immigrant individuals, a demonstration of the social flexibility of this species orthogonal to their evolved xenophobic propensities.