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Keywords:

  • chimpanzees;
  • Pan troglodytes;
  • group formation;
  • introduction;
  • aggression;
  • captive;
  • grooming

Abstract

Descriptions of the formation of relatively large groups of unfamiliar chimpanzees (Pan troglodytes) in captivity are scarce in the literature. Nineteen chimpanzees from preexisting subgroups were introduced into a social group at the Yerkes Regional Primate Research Center. The group included two adult males, six adult females along with six dependent infants, and five unrelated juveniles, four of whom had been hand-raised in a nursery unit. Here we provide details on dyadic and multiparty introductions as well as technical details on the indoor/outdoor compound. The introduction process itself took more than 3 weeks, and was completed without major injuries. The introductions combined with 4 years of follow-up data on aggression, grooming, and affiliative behavior confirm that even chimpanzees from an environment that does not promote complex social skills can be formed into a large multimale–multifemale group. During the introductions, low rates of agonistic behavior among adult females were offset by high rates of affiliative behavior. The two adult males, however, showed contact aggression during the first 10 minutes, after which such behavior virtually disappeared, whereas affiliative behavior increased. Three months after their first introduction, the two males reversed dominance ranks within the group, and hierarchical stability has been maintained since. During the 4-year postintroductory period, grooming rates slightly decreased, but group cohesion was maintained. The frequency of aggression among all adults, including the males, increased during the 4-year period, but aggression was generally of low intensity after the first year. Zoo Biol 20:501–515, 2001. © 2002 Wiley-Liss, Inc.