Huddling relationships in night sleeping groups among wild Japanese macaques in Kinkazan Island during winter |
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Authors: | Hiroyuki Takahashi |
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Institution: | (1) Department of Zoology, Faculty of Science, Kyoto University, Sakyo-ku, 606-01 Kyoto, Japan |
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Abstract: | Huddling groups at sleeping sites, and allogrooming and proximity in the daytime during winter, were examined in a wild Japanese
macaque (Macaca fuscata) troop on Kinkazan Island in the non-snowy district of northern Japan. All sleeping groups, defined as a cluster in which
individuals huddle at sleeping sites, were formed on the ground. Their sizes tended to increase when the temperature was lower.
The number of adults with mutual physical contact in sleeping groups increased when the size of sleeping groups increased.
These results suggest that the physiological function of huddling is protection from low temperatures, and that macaques select
the ground as sleeping sites to form large sized groups. Huddling was performed most frequently among kin dyads. Non-related
dyads which appeared to be affiliative in the daytime also huddled frequently at sleeping sites. Even non-related dyads which
showed affiliative behavior less frequently in the daytime exhibited huddling, at night, however, they did so less often than
those of kin dyads and affiliated dyads. It appears that huddling at night by pairs that did not normally affiliate in the
daytime was made possible by the increased tolerance of individuals responding to colder temperatures at night in winter.
Furthermore, huddling, grooming, and proximity were exhibited at greater frequency between kin dyads, and between high-ranking
males and specific females of kin groups, although the dyads of individuals older than 15 years often were involved only in
huddling. These results suggest that two types of social bonds exist at sleeping sites in winter. One is the social bond common
to both the daytime and nighttime, the other is peculiar to nighttime. Consequently, the social function of huddling is that,
troop integration might increase at sleeping sites in winter as close social relationships among adults are extended more
widely than those in daytime. |
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Keywords: | Macaca fuscata Huddling Sleeping group Winter Cool temperature zone |
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