Habitat
Lowland and hilly tropical rainforest, including dipterocarp and peat-swamp forest. The
habitat is almost wholly arboreal and orang-utans are found at all levels of the forest.
Geographical spread
Two subspecies found only in Borneo (P.p. abelii)in Sabah,
Sarawak and Kalimantan in lowland primary rainforest and Sumatra (P.p. pygmaeus) in Atjeh,
the mountainous region of the northwest.
Current population
Estimate 6,000 in Sumatra and 37,000 in Borneo (Rijksen 1986).
Status
The orang-utan is classified as endangered by the IUCN and the USDI and is on
appendix 1 of CITES.
Size
Male- head and body 97cm, height 37cm. Female- head and body 78cm, height 115cm.
Weight
Male 60-90kg (130-200lb), female 40-50kg (88-110lb).
Average life expectancy
35 years (50 years in captivity).
Normal diet
Predominately frugivorous including mango, figs, lychees, jackfruits and durian,
with some insects such as ants, termites and honey bees. In stormy monsoon months when
fruit is less available they eat leaves, bark and pith. They also eat mineral-rich soil and
occasionally eggs and small vertebrates such as birds and squirrels. Water is drunk from tree
holes by dipping in a hand and sucking the water-drops that fall from its wrist.
Normal lifestyle
Rather solitary, although local variation has been reported in the social
structure of the orang-utan. The most common group is adult female and one or two young.
Adult males occupy home ranges that overlap the territories of several females. The male uses
loud calls as a spacing mechanism and discourages the approach of other males by bellowing
and by branch-shaking displays. Although contact between males invariably leads to aggression
or marked avoidance, females will pair up together, travelling and feeding for up to three days.
At night they use vegetation to construct a large platform nest in the trees where they sleep.
Generally a new nest is made each night.
Since orang-utans are long-lived their breeding strategy is based on producing a few high
quality, well-cared for young. The female normally produces a single young although twins are
occasionally born. The young are exclusively cared for by the female and they ride on her back
until they are about 2 and a half years old. The interbirth period is about 3-4 years. Once the
female has another infant, the older sibling becomes increasingly independent but may still seek
its mothers protection until its about 7 or 8. Females are sexually mature at 7 years, whilst
males reach reproductive capability at 13-15 years.
Previous geographical spread
The orang-utan once had a greater range; in Sumatra
distribution of orang-utans has declined by 20-30% since 1935-38 and is only found now in the
northern part of the island. Pleistocene remains of ancient orang-utans have been found in
China.
Reasons for decline
Orang-utans have been killed maybe in part because of its resemblance
to man and as an alternative to headhunting. Through much of the twentieth century a major
threat was the collection of young animals (which requires the mother to be killed) for exhibition
in zoos and circuses and for pets. Although orang-utans are now protected by law in the
countries in which it lives, baby orang-utans are still taken from the wild for the pet trade.
Keeping an orang-utan was recently popularised in an Asian soap-opera, where it was shown
to be the perfect pet. For every baby that survives, a female has been killed and at least 4
young have died along the way.
Current threats
The greatest current problem however,is the logging of forests in which the
orang-utans live.
Conservation projects
The only way to conserve these animals in the short-term is to set up
parks and reserves where the habitat is protected. Reserves have been successfully set-up in
Malaysia and Indonesia, such as the Gunung Leuser National Park in Sumatra, Tandjung
Puting and Kutai National Parks and Gunung Palung and Bukit Raja reserves in Kalimatan
(Indonesian Borneo), Lanjak Entimau reserve in Sarawak. Several rehabilitation stations have
been established in Malaysai and Indonesia to train confiscated young pet orang-utans to
return to the wild. The Taiwan Orang-utan Foundation are releasing the rehabilitated animals
into protected areas where wild orang-utans no longer occur in order to establish new
populations. Some success has been achieved in drawing local peoples attention to the plight
of these great apes.
File last modified Thursday, October 3, 1996