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Wild Orangutans

OFI's Wild Orangutan Studies

Studying Wild Orangutans

Wild orangutan Pete and Pamela,

Wild orangutan Pete has been observed by Dr. Biruté Mary Galdikas since 1972. Her latest offspring, Pamela, was named after the Canadian actor, Pamela Anderson.

Camp Leakey was established in 1971 as a base camp to study a population of wild orangutans in the northwestern part of Tanjung Puting National Park. Camp Leakey is associated with a 50 km2 (19.3 square miles) grid of narrow forest trails initially cut and mapped by Rod Brindamour. Currently over 100 kilometers of trails exist and are used by OFI staff to quickly access different spots in the study area.

The ecology of the study area mirrors much of Tanjung Puting. The Sekonyer Kanan River which forms the western boundary of the study area is a black water river system. Over one third of the study area consists of tropical peat swamp forests which are frequently associated with black water rivers. Much of the rest of the study area consists of tropical heath forests, parts of which are so rich that areas of forest have been called mixed dipterocarp forest. The swamp forests interdigitate with dry ground forest in the study area providing orangutans with food from several ecozones.

Currently over 100 kilometers of trails exist and are used by OFI staff to quickly access different spots in the study area”

Thus, in Tanjung Puting the abundance of fruit, the preferred food of orangutans, is enhanced by the fact that orangutans utilize fruit from several different forest types with different species of trees, frequently fruiting at different times. Although there is some predictable seasonality in fruit abundance, fruit is not particularly abundant during parts of the year. Orangutans utilize bark and young leaves during those times to supplement fruit. The research at Camp Leakey has helped elucidate the complex foraging pattern of orangutans over the years.

The wild orangutan research carried out at the Camp Leakey study area has been going on for 40 years and has been described as “monumental” by an anonymous reviewer. It is one of the longest continuous studies on any wild animal population ever carried out in the history of science. Over 150,000 hours of observation have been accumulated over the years on the wild orangutan population. The goal of the research is to document individual orangutan life histories in order to test various hypotheses about orangutan adaptation. The research at Camp Leakey was the first to elucidate the extreme birth intervals of orangutan females (7.7 years between offspring), to document repeated combats among adult male orangutans in the presence of receptive females, and to document the wide variety of food wild orangutans utilized.

Also documented in the Camp Leakey study was the fact that orangutans at Tanjung Puting were semi-solitary, rather than solitary as previously documented in other parts of Borneo. The gregarious nature of independent immature orangutans was also confirmed. Adolescent females were almost social in that they spent much time with their natal units (mother and younger sibling) as well as with other adolescent females, subadult and adult males as well as with the occasional adult female who was not their mother. Subadult males, on the other hand, tended to associate mainly with females.

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