School of Biological & Earth Sciences, Liverpool John Moores University The Long-Term Eects of Reconciliation in Japanese Macaques Macaca fuscata Nicola F. Koyama Koyama, N. F. 2001: The long-term eects of reconciliation in Japanese macaques Macaca fuscata. Ethology 107, 975Ð987. Abstract With one exception, all previous studies of reconciliation in non-human primates (friendly reunion between former opponents) have focused on demon- strating the immediate, short-term eects despite the widely held view that reconciliation has a long-term function of repairing social relationships following aggression. To investigate this long-term function I compared mean interaction rates between opponents during the 10 d following reconciled and non-reconciled con¯icts to baseline levels of interaction. Aggression rates during the 10 d after non-reconciled con¯icts were signi®cantly higher than the baseline rate, whereas after reconciled con¯icts aggression was minimal. Similarly, grooming, proximity and approach rates during the 10 d after non-reconciled con¯icts were signi®- cantly lower than the baseline rate whereas grooming, proximity and approach rates in the 10 d after reconciled con¯icts were restored to baseline levels. These results indicate that there are consequences to not reconciling with a former opponent and highlight the fact that these may be costly in terms of increased risk of long-term aggression and reduced aliation. The data support predictions from the Relationship-Repair Hypothesis suggesting that reconciliation functions as a mechanism for the repair of social relationships damaged by aggression. School of Biological and Earth Sciences, Liverpool John Moores University, James Parsons Building, Byrom Street, Liverpool L3 3AF, England. E-mail: N.F.Koyama@livjm.ac.uk Introduction Shortly after an aggressive con¯ict, former opponents often engage in friendly interactions. Over the past two decades friendly post-con¯ict (PC) interactions have been studied intensively in many species of non-human primates (for a review see Aureli & de Waal 2000); more recently similar studies have been carried out in children (Cords & Killen 1998; Verbeek et al. 2000) and Ethology 107, 975Ð987 (2001) Ó 2001 Blackwell Wissenschafts-Verlag, Berlin ISSN 0179±1613 U. S. Copyright Clearance Center Code Statement: 0179-1613/2001/10711±0975$15.00/0 www.blackwell.de/synergy