A Statistical Modelling Approach to the Occurrence and Timing of Reconciliation in Wild Japanese Macaques Bonaventura Majolo*, Raffaella Ventura & Nicola F. Koyamaà * Department of Psychology, University of Lincoln, Lincoln, UK  Scottish Primate Research Group, School of Social and Health Sciences – Division of Psychology, University of Abertay Dundee, Dundee, UK à Research Centre in Evolutionary Anthropology & Palaeoecology, School of Natural Science & Psychology, Liverpool John Moores University, Liverpool, UK Introduction Reconciliation, ‘the post-conflict friendly reunion of former opponents that restores their social relation- ship disturbed by the conflict’ (Aureli & de Waal 2000; p. 387), was first formally described in chim- panzees almost 30 yr ago (de Waal & van Roosmalen 1979). Since de Waal and van Roosmalen’s seminal Correspondence Bonaventura Majolo, Department of Psychology, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, UK. E-mail: bmajolo@lincoln.ac.uk Received: July 25, 2008 Initial acceptance: August 31, 2008 Final acceptance: October 1, 2008 (J. Wright) doi: 10.1111/j.1439-0310.2008.01591.x Abstract In various social species, animals have been observed to share friendly relationships with some group members and to resolve conflicts through reconciliation, the exchange of affiliative behaviour soon after a conflict that functions to restore the relationship between the former opponents. The valuable relationship hypothesis predicts that reconciliation should be observed more often after conflicts between friends. Friendly rela- tionships can be described by three dimensions (i.e. value, security and compatibility); however, research into the relative importance of these dimensions for the occurrence of reconciliation is sparse. Moreover, rec- onciliation may depend on factors other than the social relationship between opponents including, for example, their social status or the context of the conflict. Our study aimed at analysing which factors are important determinants of reconciliation and at testing the valuable relationship hypothesis, by analysing the relative effects of relationship value, security and compatibility on the occurrence and timing of recon- ciliation. We collected data on two troops of wild Japanese macaques living on Yakushima Island, Japan, and selected the best predicting vari- ables of reconciliation using linear mixed models. Our results show that reconciliation occurs more frequently, and earlier, after conflicts between opponents who exchange a higher percentage of grooming. Two additional variables related to relationship security and value were selected in the best models: frequency of aggression and of approaches resulting in tolerated co-feeding. Among the variables not related to relationship quality, distance between opponents at the end of the con- flict, kinship, sex of the opponents and context of conflict (i.e. during feeding or social time) were included in our models. Our findings sup- port the valuable relationship hypothesis and, in particular, highlight that the fitness-related benefits of social relationships (i.e. the relation- ship value) are important determinants of the evolution of friendly rela- tionships and reconciliation. Ethology Ethology 115 (2009) 152–166 ª 2009 The Authors 152 Journal compilation ª 2009 Blackwell Verlag, Berlin