, Volume 40, Issue 2, pp 365–381 | Cite as

Sociological and demographic characteristics of a recently found arsi gelada population in ethiopia

  • Akio Mori
  • Toshitaka Iwamoto
  • Umeyo Mori
  • Afework Bekele


A new population of gelada baboons isolated from other known gelada populations living on the opposite side of the Rift Valley was found in 1989 in the Arsi region of Ethiopia (Mori &Belay, 1990). Subsequent observations were conducted on the new gelada population in three study periods of 16 to 55 days over three consecutive years, 1994–1996. When we compare this population with other well studied northern populations, densities were lower, band size was smaller and the ratio of juveniles to adult females was lower. Based onOhsawa andDunbar's (1984) criteria these results suggest that this population exploits the harshest environment among known gelada populations. This may be due to the severe effect of the dry season at low altitude in the study site. Band size was small in the study site. Association rates of units were low, and each unit behaved more independently than those of northern populations. Age-sex composition of units changed drastically between consecutive study periods, indicating unstable unit structure. Moreover, there seems to be a tendency in this population whereby several adult males easily invade and are incorporated into a unit but the unit is expected to thereafter divide. The phenomenon can be explained by two factors: (1) Each unit fed rather independently in this area, where units fed intensively on both plateau and the slope of the cliff; and (2) Males may be incorporated in a unit for defense against leopards. As the units were vary small in size and unstable as compared with the Semien gelada units, the traditional concept of a stable gelada unit formed by blood related females, does not seem to fit this population.

Key Words

Gelada baboons Demography Population Social change 


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Copyright information

© Japan Monkey Centre 1999

Authors and Affiliations

  • Akio Mori
    • 1
  • Toshitaka Iwamoto
    • 2
  • Umeyo Mori
    • 3
  • Afework Bekele
    • 4
  1. 1.Primate Research InstituteKyoto UniversityAichiJapan
  2. 2.Faculty of EducationMiyazaki University, 1-1Miyazaki, MiyazakiJapan
  3. 3.Nagoya Bunri CollegeAichiJapan
  4. 4.Department of Biology, Science FacultyAddis Ababa UniversityAddis AbabaEthiopia

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