Association,ranging, and the social unit in chimpanzees of the Mahale Mountains,Tanzania |
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Authors: | Kenji Kawanaka |
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Institution: | (1) Laboratory of Anthropology, Okayama University of Science, 1-1, Ridai-cho, 700 Okayama, Japan |
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Abstract: | In order to characterize the social unit in chimpanzees, about which several conflicting views have been proposed, the proximity
matrix among 55 recognized chimpanzees and the range covered by each of them are examined, on the basis of data obtained at
the Mahale Mountains during 12 months in 1978–1979. It is shown once again that chimpanzees have a bisexual social unit (unit-group).
Two such unit-groups were detected in the study area. All animals belonged to one of the two unit-groups except a few cycling
females (and a juvenile male accompanied by his cycling mother) which were seen to associate alternately with members of two
neighboring unit-groups, covering a whole range of one or even two unit-groups. The problem of such females is discussed in
relation to the spatial relationships between the two unit-groups. Reexamining the membership of a unit-group, it is demonstrated
that a unit-group was most likely patrilineal. While nulliparous females transferred between unit-groups, parous females tended
to remain in a unit-group where they first gave birth to infants and to have several offspring therein. This appeared significant
for ensuring recruitment of members of the next generation to a patrilineal unit-group. Although some adult males left their
natal unit-group, they never joined the other. Male departure from a unit-group seemed to be forced by the other males and
to be the sociological equivalent of going into exile, which is unique in nonhuman primates. |
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Keywords: | chimpanzee association pattern ranging pattern bisexual social unit patrilineal group |
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