Bornean Orangutan (Pongo pygmaeus): Facts and Habitat

What does a Bornean orangutan look like?

Bornean orangutans have coarse, shaggy, reddish-brown hair that is darker than that of their Sumatran relatives, covering gray to black skin. Their arms are extremely long compared with their short legs: an adult male’s arm span can reach about 2 m (6.5 ft). Both hands and feet have curved fingers and toes that work like hooks for gripping branches, and the big toe is opposable like a thumb.

The two sexes look very different. Females and young males have a fairly small, rounded face. Dominant adult males develop large fleshy cheek pads, called flanges, that stick out to the sides of the face and are mostly made of fat. These “flanged” males also grow a big, hanging throat sac, long hair and often a beard. The Bornean male’s flanges are typically broader and more fleshy than those of Sumatran males.

Not every adult male grows flanges. Some stay “unflanged” for years, looking like large females, and only develop cheek pads once there is no dominant male nearby. Both types of male can father young.

How big is a Bornean orangutan?

The Bornean orangutan is the third-largest ape after the two gorilla species, and the heaviest animal that lives mainly in trees. Males are about twice as heavy as females.

Captive orangutans with little exercise can become much heavier than wild ones, sometimes more than 150 kg (330 lb). For comparison with Africa’s great apes, see the western gorilla, which can weigh twice as much as a male orangutan.

Habitat and range

Bornean orangutans live only on Borneo, the third-largest island in the world, which is shared by Indonesia (Kalimantan), Malaysia (Sabah and Sarawak) and Brunei. They are found in lowland dipterocarp forest, peat swamp forest, freshwater swamp forest and hill forest up to about 1,500 m (4,900 ft). The highest densities are in lowland and peat swamp forests near rivers, where fruit is most plentiful.

Scientists recognize three subspecies, each in a different part of the island:

• Northwest Bornean orangutan (P. p. pygmaeus): Sarawak and northern West Kalimantan; the rarest subspecies.
• Central Bornean orangutan (P. p. wurmbii): southern West Kalimantan and Central Kalimantan; the largest population, including Sabangau and Tanjung Puting.
• Northeast Bornean orangutan (P. p. morio): East Kalimantan and Sabah; the smallest of the three in body size.

Their range today is patchy, broken up by plantations, roads and rivers. Fossil teeth show that orangutans once lived across much of mainland Southeast Asia and southern China, as well as on Java. Read more in where do orangutans live?

What do Bornean orangutans eat?

Orangutans are mainly fruit eaters. When fruit is plentiful they spend most of their feeding time on soft, sugary fruit such as wild figs, durian and the fruits of many other forest trees and vines. Researchers have recorded several hundred different plant foods in the diet of a single population.

Borneo’s forests are unusual because many trees fruit together in irregular “mast” years and then produce little for long periods. In lean times Bornean orangutans fall back on young leaves, shoots, pith and especially the inner bark of trees, and they lose body fat until fruit returns. They also eat flowers, honey, termites, ants, bird eggs and mineral-rich soil, and very rarely a small mammal such as a slow loris. See what do orangutans eat? for a fuller picture.

Behavior: life in the trees

Orangutans are the most arboreal of the great apes. They move slowly and carefully, climbing with all four limbs, hanging below branches and swaying thin trees back and forth until they can reach the next one. Bornean orangutans, especially heavy males, also walk on the ground more often than Sumatran orangutans, perhaps because Borneo has no tigers.

They are the most solitary great apes. Adult females travel with their dependent young in overlapping home ranges, while adult males roam more widely and usually avoid each other. Orangutans may gather peacefully at a large fruiting fig tree, and young animals often seek out playmates.

Every evening an orangutan builds a sleeping nest high in a tree by bending and weaving branches into a platform, often lining it with leafy twigs as a mattress and sometimes adding a “roof” against rain. A new nest takes only a few minutes, and smaller day nests are built for resting.

Flanged males make “long calls”, a series of deep roars and bellows lasting a minute or more that can be heard about a kilometer away through the forest. Females use the calls to find preferred males, and other males use them to keep their distance.

Intelligence and tool use

Orangutans are among the most intelligent animals. In the wild, Bornean orangutans have been seen using leaves as napkins and as “gloves” for handling spiny fruit, holding leafy branches over their heads as umbrellas in the rain, using sticks to scratch themselves, and holding leaves to their lips to change the sound of their “kiss squeak” alarm call. Different populations have different habits, which many researchers interpret as simple cultures passed on by learning. Sumatran orangutans are even more skilled tool users, using sticks to extract insects and seeds.

Reproduction and life cycle

Females usually give birth for the first time at about 14 to 16 years old, after a pregnancy of about 8.5 to 9 months. A single infant is born, weighing about 1.5–2 kg (3.3–4.4 lb); twins are rare. The baby clings to its mother’s hair and is carried constantly for its first years, sleeps in her nest and is nursed for many years.

Young Bornean orangutans usually stay with their mothers until they are about 6 to 8 years old, learning which foods to eat, where to find them and how to build nests. Because a mother does not breed again until her young is nearly independent, the gap between births is about 6 to 8 years in Bornean orangutans. A female may raise only four or five young in her whole life, one of the slowest rates of reproduction of any mammal. Learn more in how long do orangutans stay with their mothers?

Males reach sexual maturity at around 15 years, but may not develop flanges until much later.

How long do Bornean orangutans live?

Wild Bornean orangutans are thought to live about 35 to 45 years, and some may live longer. In zoos they can reach about 50 to 60 years. One of the oldest well-documented orangutans, Puan, a Sumatran orangutan at Perth Zoo in Australia, died in 2018 at about 62 years old.

Predators and threats

Adult orangutans have few natural predators on Borneo; Sunda clouded leopards may take young animals. By far the biggest threats come from people:

• Habitat loss: lowland forest has been cleared on a huge scale for oil palm and pulpwood plantations, logging, mining and farming.
• Fires: draining peat swamps for agriculture makes them burn easily, and severe fires in 1997–98 and 2015 destroyed large areas of orangutan habitat.
• Killing: orangutans are killed for meat, in conflicts when they raid crops, and when mothers are shot so their babies can be sold illegally as pets. A survey of villages in Kalimantan estimated that 750 to 1,800 orangutans were killed there in a single year in the late 2000s.

Conservation status

The IUCN Red List moved the Bornean orangutan from Endangered to Critically Endangered in 2016, the highest category before extinction in the wild. Its 2016 assessment estimated about 104,700 Bornean orangutans and projected a decline of more than 80% over three generations (about 75 years). A 2018 study found that Borneo lost more than 100,000 orangutans between 1999 and 2015, and populations keep shrinking because the animals breed so slowly.

The species is protected by law in Indonesia and Malaysia and listed on CITES Appendix I, which bans international commercial trade. Protected areas such as Tanjung Puting, Sabangau and Danum Valley, together with rescue and rehabilitation centers like Sepilok in Sabah and Nyaru Menteng in Central Kalimantan, play an important role. The other two orangutan species, Sumatran and Tapanuli, are also Critically Endangered. Read more in why are orangutans endangered? and how many orangutan species are there?

Myths and facts

• Myth: orangutans are monkeys. Fact: they are great apes, with no tail and a larger brain, closely related to gorillas, chimpanzees and humans.
• Myth: “orangutan” ends in -ang. Fact: the spelling “orangutang” is common, but the generally accepted English name ends in -an.
• Myth: orangutans live in big troops. Fact: they are the most solitary of all great apes; the strongest bond is between a mother and her young.