Variation in conciliatory tendency and relationship quality across groups of pigtail macaques

Previous studies suggest that the tendency for primates to reconcile after agonistic conflict is related to the quality of relationships between opponents: the 'relationship quality' hypothesis. In addition, reconciliation frequency seems to covary with other social variables such as the rate of allogrooming, the intensity of aggression and the outcome of approaches: the 'systematic variation' hypothesis. It is proposed that such systematic variation should be present not only between different species but also between different groups of the same species. To test these hypotheses, data were collected from two large corral-housed groups of pigtail macaques, Macaca nemestrina, over 7 months. The two groups lived in identical environments but one was well established, the other newly formed. In both groups, conflicts were more frequently reconciled between opponents with strong affiliative ties, as predicted by the relationship quality hypothesis. Members of the well-established group reconciled roughly twice as often as members of the newly formed group. Contrary to the predictions of the systematic variation hypothesis, other social variables did not vary between groups. Members of the well-established group, however, distributed their affiliative behaviour less evenly, focusing their efforts on a relatively small number of partners. The concentrated social networks in the well-established group apparently produced more intense ties, hence increasing the likelihood of reconciliation after conflict. These results show that detailed analyses of social networks provide a tool to investigate the systematic variation hypothesis when variation is subtle, such as between groups of the same species. The study confirms the relationship quality hypothesis at both the within- and between-group level, provides support for a more sophisticated concept of systematic variation, and illustrates the special usefulness of reconciliation measures as a gauge of social integration. (C) 1996 The Association for the Study of Animal Behaviour