A new approach to evaluating troop deployment in wild Japanese Monkeys

In winter when the mountain slopes are covered with deep snow, it is easy to obtain quantitative data on the two-dimensional deployment of members of a troop of wild Japanese monkeys. We observed the deployment of a troop on a slope from the opposite side of a river. The deployment patterns, evaluated on the basis of the relative distance from the central point (centroid) of the troop, were different for each sex and age category. Adult females, infants, and 1-year-olds tended to be grouped together and were concentrated near the center of the troop. On the other hand, adult males were randomly spaced. These tendencies suggest that the deployment reflects the social structure of the duplicate concentric-circle model originally proposed by J. Itani (1954).