Identifying inter-individual social distances in Japanese monkeys

Japanese monkeys (Macaca fuscata) appear to recognize three types of inter-individual distances: (1) intimate distance less than 1 m, (2) personal distance 1–3 m and 1–5 m (close and far phase), and (3) social distance 3 or 5 m variable outer limit. The boundary between intimate and personal distance, 1 m, works as a protective sphere around individuals. Because personal distance reflects an existence of individuals, we defined this distance as a basic distance among three types. We reviewed related studies and found that Japanese monkeys change their inter-individual distances according to social and ecological circumstances. Additionally, we suggest that these three types of distances can be applicable across the Macaca species.