Observation of a wild Japanese macaque mother pacifying her distressed infant with an acorn

This is the first report on an observation of food transfer by a mother to her offspring in wild Japanese macaques (Macaca fuscata yakui). On November 6, 1996, an adult female wild Japanese macaque stopped grooming her 1.5–1.6 yr old daughter in order to be groomed by a young male. Her daughter protested loudly for about 1 min. In response to her daughter's protest, the mother picked up a mature nut ofQuercus phillyraeoides that was lying near her right hand, and placed it in the daughter's mouth. The daughter's cries were immediately muffled and she silently ate the acorn's contents, and spat out the pericarp. We inferred that the daughter wanted to be groomed by her mother, not to receive food. This reported example of treatment resembling tool using behavior in response to an emotional outcry was precipitated by mother-offspring conflict in the natural habitat.