Sustainability

Populations of orangutan are restricted to pockets of forest on the islands of Borneo and Sumatra. Bornean orangutan is endangered and the subspecies that is found in Sabah and in Danum Valley Consercation Centre is Pongo pygmaeus morio (East Kalimantan & Sabah).

The Primate Research Institute (PRI) of Kyoto University had a long tradition of fieldwork in non-human primates in Southeast Asia. Their Danum Orang Utan Research Project (DORP) has been stationed in BRL in 2006 and they have been studying the orangutans around here ever since. Researchers have observed and named 65 orangutan individuals around BRL. Over times, some have passed or disappear but there are also new-borns.

The orangutans are generally passive but can be territorial and aggressive towards other orangutans. The adult male orangutan has a unique social and physical system named “Bimaturism”. Bimaturism also refer to developmental differences within a sex (in this case, the male) related to secondary sex characteristics. Hence there are two types of adult male, “Flanged Male” and “Unflanged Male”. The Flanged Male has a remarkable secondary sexual characteristics such as large body size (twice than adult female), cheek flanges and throat-pouch.

The Flanged Male is very aggressive towards other Flanged Male while it is tolerant towards the Unflanged Male. The Unflanged males will try to mate with any female and may succeed in forcibly copulating with her if she is also immature and not strong enough to fend him off. Mature females can easily fend off their immature suitors, preferring to mate with a flanged male.

The natural habitat of orangutan is limited areas of tropical rainforest, low land Dipterocarp forest and swamp forest at altitudes of less than 1000m. The orangutan has a slow and long life history. Duration of life is estimated over 50 years in the wild. The female matures sexually at about ten years old and male matures around 15 years old. The female has a baby every six or nine years. Therefore its reproductive speed is the slowest in mammals and this is one of the reasons the orangutan is in danger of extinction. A remarkable characteristic of the orangutan is that it is the largest arboreal mammal (Adult Female: 35 kg, Adult Male: 80 kg) living on earth.

The orangutan is a fruit-eating animal and loves fruits of wild durian, wild mangosteen, ficus and so on. However in the primary forest in Borneo where there are “long period of scarcity of fruits”, sometimes over several years, the orangutan then depends on young leaves and barks for food. They also feed ants and termites but they hardly eat vertebrates.

The orangutan stays on trees, sometimes over 30m above the ground, as there are fewer predators, especially in Borneo. They use leaves to make rainhats and branches as well as foliage too for roofs over the sleeping nests every night. The baby sleeps with the mother in the same nest while the young and the adults make their own nest and sleep alone.