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Classification and Distribution of Orangutan
Fossil evidence suggests that till 10,000 years ago, distribution of orangutan extended to across Java and mainland Asia (China, Vietnam, Laos, Cambodia and Thailand). The orangutan in Java Island may have become extinct in the 17th century. Today, populations are restricted to pockets of forest on the islands of Borneo and Sumatra. Before these two populations were classified as two subspecies but now they are divided into two species, Borneo Orangutan: Pongo pygmaeus and Sumatara Orangutan: Pongo abelii. The Borneo Orangutan is further categorized into three subspecies; P. p. pygmaeus (Sarawak & West Kalimantan), P. p. wurmbii (West & Central Kalimantan) and P. p. morio (East Kalimantan & Sabah).

The current population of orangutan in Sumatra Island is 6,500 and 54,000 in Borneo Island. A  total of 60,500 orangutans live in the world. Sabah has 11,000 orangutans in 13 populations but 62% of them live outside of the protected areas (commercial forests). The number of orangutan living in Danum Valley Conservation Area is estimated at 500.

Ecology of Orangutan
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.

Sociality of The Orangutan
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”. 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 the 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.

Extinction and Conservation of Orangutan
The number of Orangutan decreased over 40% in the twentieth century due to habitat destruction and poaching. Previous logging activities and oil palm plantation had a great influence on the decrease of the orangutan. In the longer term, this loss of habitat may cause the population to decline further. When adult females are killed, the babies will be sold and the skull of the dead will be used to create as a souvenir that are sold illegally.

We need to cultivate the knowledge of people to be part of the world’s largest primate rescue and rehabilitation project and help save the orangutan from extinction. Rehabilitation programs from the government in Malaysian and other NGOs have contributed to conserve the orangutan.

Footnote
Our sincere appreciation to Dr Noko Kuze and her team for the generous contribution on the research information and pictorial of the orangutan in Danum Valley Conservation Area for the purpose of the development of this webpage.





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