Demographic study of a large-sized unit-group of chimpanzees in the mahale mountains,Tanzania: A preliminary report |
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| Authors: | Mariko Hiraiwa-Hasegawa Toshikazu Hasegawa Toshisada Nishida |
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| Affiliation: | (1) Department of Anthropology, Faculty of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113 Tokyo, Japan;(2) Department of Psychology, College of Arts and Sciences, The University of Tokyo, Komada, Meguro-ku, 153 Tokyo, Japan |
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| Abstract: | Long-term demographic observations on a large-sized unit-group of chimpanzees in the Mahale Mountains, Tanzania, are summarized. The unit-group, the M group, contains over 100 individuals, which makes it the largest unit-group ever reported. The age-sex composition, natality, mortality and transfers of the M group are analyzed. An attempt is made to illustrate an age-sex pyramid of the group by estimating the ages of all the individuals in the group. The results reveal that: (1) the mortality rate of the male infants within 1 year almost doubled that of female infant; (2) adult male to adult female ratio of the M group is considerably higher than any other unit-groups elsewhere; and (3) the M group contains a relatively large number of old animals over 40 years of age, suggesting that the longevity of wild chimpanzees might be greater than estimated so far. |
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