Female emigration in Japanese macaques, Macaca fuscata: ecological and social backgrounds and its biogeographical implications

Yamato Tsuji and Yukimaru Sugiyama

We reviewed case studies in female Japanese macaques engaged in social and spatial emigration. In such instances, animals leave their natal group and remain alone or in a small group, transfer to another group, or join extra-group males to establish a new group. Since 1953, at least 34 emigration cases (and at least 78 females) have been reported from eight study sites of five provisioned and three wild populations in Japan. In most cases, female emigration occurred 1) when food conditions warranted the move due to either a decrease in the artificial feeding of provisioned populations or to a seasonal deterioration in the food environment of wild populations and/or 2) when group structure was disturbed via a drastic change in size or the disappearance of adults. In most cases, subordinates were the ones who emigrated. Unlike the case in other primate species, an influx of extra-group males never led to female emigration to avoid infanticide. These suggest that decreases in per capita foraging success within the group and loss of support from kin and group males were probably principle factors motivating emigration by females. In response to environmental deterioration, females emigrate and settle within new location/range within same habitat type.

Mammalia 78: 281-290

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