Socially deprived rhesus macaques fail to reconcile: do they not attempt or not accept reconciliation?

Reconciliation, affiliation between opponents after a conflict, is an important means to reduce the detrimental effects of aggression in social primates. Socially deprived (SD) rhesus macaques, Macaca mulatta, however, do not reconcile, while socially raised animals do. This lack of reconciliation in deprived animals may be caused by (1) a lack of secure and valuable relationships, (2) having missed the opportunity to learn reconciliation as an immature, or (3) high stress levels in social situations that prevent reconciliation. It is unclear which of these factors causes the lack of reconciliation in deprived animals. We investigated these factors using newly developed measures distinguishing between the attempt to reconcile and acceptance of this attempt in captive rhesus macaques with different rearing histories. The results suggest that the absence of reconciliatory behaviour in the SD animals is not due to lack of initiation of contact and the potential to reconcile, but to rejection of affiliative approaches by the opponent after a conflict. Although we cannot exclude that SD animals did not learn to approach opponents, the results seem best explained by the hypothesis that approaches are considered threatening and avoidance of reconciliation is caused by a high anxiety level in the SD individuals.