Carrying and Washing of Grass Roots by Free-Ranging Japanese Macaques at Katsuyama

The acquisition and transmission of new feeding behaviours in Japanese macaques (Macaca fuscata) such as sweet potato washing [1, 2], wheat washing [2] and caramel eating [3, 4] have been well documented. These behaviours are all related to provisioned food. Here we report carrying and washing of grass roots by Japanese macaques in a free-ranging group. This would appear to be the first report of washing of dirt from natural food, such as grass roots, among macaques. Furthermore, some monkeys in the present study rubbed dirt from roots by rolling them along the surface of a flat rock at the edge of a river. This may be considered a tool-using behaviour.