Article

Primates

, Volume 25, Issue 4, pp 401-413

First online:

Demographic study of a large-sized unit-group of chimpanzees in the mahale mountains, Tanzania: A preliminary report

  • Mariko Hiraiwa-HasegawaAffiliated withDepartment of Anthropology, Faculty of Science, The University of Tokyo
  • , Toshikazu HasegawaAffiliated withDepartment of Anthropology, Faculty of Science, The University of Tokyo
  • , Toshisada NishidaAffiliated withDepartment of Psychology, College of Arts and Sciences, The University of Tokyo

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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.