Variation in Spatial Cohesiveness in a Group of Japanese Macaques (Macaca fuscata)
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The spatial cohesiveness of a group is an important element that characterizes the social structure of group-living species. Moreover, remaining cohesive is crucial if individuals are to coordinate their activities and reach collective decisions. We measured interindividual spacing in a group of wild Japanese macaques (Macaca fuscata) to assess the spatial cohesiveness of a social group quantitatively. We used simultaneous focal animal sampling, with 2 observers recording individuals’ locations with a global positioning system (GPS) during 3 seasons. Interindividual distances differed among seasons; they were short in autumn (mean ± SD: 25.6 ± 20.1 m), intermediate in winter (mean ± SD: 46.3 ± 35.7 m), and long in summer (mean ± SD: 62.3 ± 47.1 m). Measurements taken in summer revealed extremely wide spacing (maximum: 1225 m), suggesting subgrouping. Distances also varied with activity during each season; they were short during resting and grooming, intermediate during foraging, and long during moving. Group cohesion was also influenced by food distribution. More group members were ≤20 m of the focal individual during foraging on clumped food than foraging on scattered food in each season, and the group foraged on clumped food most frequently in autumn. Individuals were also likely to aggregate at resting/grooming sites and clumped food patches and to disperse when moving within a day. These results demonstrate that Japanese macaques show considerable variation in spatial cohesiveness both within short time periods, e.g., 1 d, and among seasons, and that they adjust group cohesiveness flexibly depending on the food conditions and foraging tactics.
KeywordsDispersion GPS Group spread Interindividual spacing Seasonal variation
We thank Professor Kosei Izawa for supporting the overall research activities on Kinkazan Island, the staff at Kinkazan Koganeyama Shrine for the use of its facilities, and Ms. Yoko Sugiura for data collection. We thank Drs. Andrew J. King, Cédric Sueur, Peter Henzi, Joanna M. Setchell, and an anonymous reviewer for valuable comments. This work was supported by a Grant-in-Aid for Scientific Research (C, No. 22570219) from JSPS to H. Sigiura, a Grant for Biodiversity Research of the 21st Century COE (A14), and a Grant for Biodiversity and Evolutionary Research of the Global COE (A06) to Kyoto University.
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