We experimentally investigated how stimulus/local enhancement, a form of indirect social influence through the physical traces typically left in the environment by previous stone handlers, might trigger stone handling behavior at the individual level, and thus could contribute to the maintenance of the stone handling tradition at the group level. Through the semi-controlled conditions of field experiments, conducted in the free-ranging provisioned Arashiyama troop of Japanese macaques, in which the stone handling tradition has been well established for nearly three decades, we our results supported the stimulus/local enhancement hypothesis.

We found that most group members preferentially directed their stone handling behavior toward the physical traces of stone handling activity (piles of stones) over randomly scattered stones. We provided evidence for the role of indirect social inputs on the long-term persistence of the stone handling tradition in Japanese macaques, through stone handling by-products, whose stimulating effect can be delayed in time and separate in space from others [REPORT]

Our findings show that even traditional behaviors with no obvious function and no apparent adaptive value, such as stone handling, can be practised on a daily basis and maintained over several years within a large proportion of group members via indirect social influences. By contrast, when a behavioral practice is restricted to a particular class of group members, it is supposed to spread very slowly and its maintenance may be jeopardized [REPORT]