Japanese macaque cultures: Inter- and intra-troop behavioural variability of stone handling patterns across 10 troops

Stone handling (SH), a form of solitary object play, consists of an individual manipulating stones by performing various behavioural patterns. Previous findings from the Arashiyama population of Japanese macaques suggested that SH is socially transmitted across generations as a behavioural tradition. To further test the hypothesis that SH is a traditional behaviour in this species, we present the most systematic inter-troop comparison of this behaviour from an investigation of nine troops of Macaca fuscata fuscata and one troop of M. f. yakui living at six sites in Japan. We analyzed a total 1280 video-recorded SH bouts and charted the relative frequency of occurrence of 45 SH behavioural patterns across age classes. Many SH patterns showed geographically patchy distributions and were referred to as local variants or SH traditions. In terms of behavioural complexity, we found three levels of SH culture, each level being defined by troop-dependent clusters of SH traditions. We found a positive correlation between geographic proximity and cultural similarity in SH between troops. To explain similarities in the SH repertoires between the free-ranging troops living at the same site, we discussed the phenomenon of cultural zones. We interpreted intra-group variability in the performance of SH patterns from the viewpoint of developmental factors. We found no major difference between the two subspecies in the occurrence and form of SH.