Effects of Hand-Rearing and Group Size on Chimpanzee (Pan troglodytes) Social Competence in Captivity

The behavior of individual animals reflects both internal states and external context. For captive animals, their early life experiences can influence later adjustment, particularly their social competence. In addition, the way in which they are housed and their current social grouping context are important factors affecting the expression of social skills. Here, the social behavior of 39 chimpanzees (<i>Pan troglodytes</i>) was observed to assess whether differences existed due to how the apes were reared and grouped. Behaviors recorded related specifically to five main components: Sociability, Grooming, Play, Responsibility and Aggression. Chimpanzees in larger groups groomed and played more, while those housed in pairs or trios displayed more and spent more time alone. Mother-reared chimpanzees took more responsibility for soliciting grooming, and interactions between grouping and rearing on chimpanzee agonistic display rates highlighted how both hand- and mother-reared chimpanzees display more if housed in small groups rather than large. Implications for the optimal management and welfare of this highly intelligent and social species are discussed in light of the importance of early life experiences in modulating the impact of current social environment on chimpanzee social profiles.