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. 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
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.
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
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
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
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.