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Date of Award


Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)


Biological Sciences

First Advisor

Richard Tenaza

First Committee Member

Steven C. Anderson

Second Committee Member

Lee Christianson


The following study was conducted from August to November of 1991 on North Pagai Island in the Mentawai Archipelago, Indonesia. The purpose of the study was to obtain preliminary information on the ecology and behavior of the four Mentawai endemic primates: Hylobatcs klossii, Macaca pagensis, Presbytis potenziani, and Simias concolor. All four species are considered endangered due to human activities, especially hunting and various forms of habitat destruction. Therefore, the present critical status of these primates makes their conservation and that of the Mentawai Islands' rain forest a priority.

It appears that resource partitioning occurs among the four primate species, M. pagensis occupied all vegetation levels and was less arboreal relative to the other three species which were primarily arboreal. All four species were found in forest habitat with S. concolor also occurring in forest swamp. M. pagensis and P. potenziani were found throughout the study area and only P. potenziani occupied coastal swamp. In addition, it is hypothesized here that for many P. potenziani groups, sleeping trees are located outside of the primary forest and these groups migrate on a daily basis to the forest. As a result, this may reduce interspecific competition since this species and H. klossii overlap in terms of resource use.

Group size and composition are discussed and a monogamous social organization was identified for H. klossii and P. potenziani while M. pagensis. was found to form polygamous families. S. concolor is identified as forming one-male polygamous groups, however, based on my observations it might initially be interpreted that this species formed monogamous groups in the study area.

Most behaviors, such as parental care, aggression, grooming, play, and feeding behavior, were rarely observed due to the wanness of these primates. Alarm response to detection of humans is discussed and distraction-like behaviors are described for each of the species.

Population density was determined for each species and these values corresponded to those found in other studies although all values in this study were relatively low compared to other studies.



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