Bornean Orangutan — facts, diet, habitat & conservation

The Bornean orangutan is the great ape of Southeast Asia — a heavy, red-haired, deliberate animal that lives its life in the treetops of the rainforest, mostly alone, navigating by a remembered map of the forest’s fruit. Its name means “person of the forest,” and it is now one of the most endangered large animals on the planet.

Overview

Bornean orangutans live only on the island of Borneo, historically throughout its lowland and hill forests, peat swamps, and river valleys. Today they are concentrated in the remaining blocks of forest, increasingly small and separated. They are the most arboreal of the great apes, spending almost all their time in the canopy, and the most solitary, with adult males in particular ranging alone over large areas.

Life in the canopy

An orangutan’s body is built for climbing and clambering rather than walking. The arms are extremely long and powerful, the hip joints exceptionally mobile, the hands and feet all able to grip like hands, and the body relatively heavy — so an orangutan moves carefully, testing branches, bridging gaps by swaying trees back and forth, rather than leaping. Each evening it bends branches into a sleeping nest, and it may build a rough day nest for resting too.

Intelligence and culture

Orangutans are among the most intelligent animals. Wild populations show tool use that varies between regions like culture — using sticks to extract seeds from spiny fruit or to probe for insects and honey, leaves as gloves, napkins, and rain hats — and in captivity they solve complex problems, use sign language and symbols, and plan ahead, including announcing their intended travel direction the evening before with a long call.

Reproduction

Orangutans reproduce more slowly than any other land mammal. A female does not give birth until around 15 years old and then produces a single infant only once every six to eight years, nursing and carrying it for the first years of life and keeping it with her until it is seven or eight. This means a population devastated by hunting or habitat loss recovers extraordinarily slowly — or not at all.

Threats and conservation

The Bornean orangutan is Critically Endangered, having lost more than half its numbers in about 60 years. The dominant threat is the conversion of rainforest to oil palm and timber plantations, along with logging, mining, road-building, and fire. Orangutans that survive in fragmented forest come into conflict with plantations and are killed, and infants are taken for the pet trade after their mothers are shot. Conservation depends on protecting and reconnecting large areas of forest, enforcing anti-poaching and anti-trafficking laws, rehabilitating and releasing orphaned and displaced orangutans, and reforming how palm oil is produced.

Bornean Orangutan: common questions

How many species of orangutan are there?

Three, all Critically Endangered. The Bornean orangutan (Pongo pygmaeus) and the Sumatran orangutan (Pongo abelii) were recognised as separate species in the 1990s, and in 2017 a small population in the Batang Toru forest of Sumatra was described as a third species, the Tapanuli orangutan (Pongo tapanuliensis) — with fewer than 800 individuals, the most endangered great ape in the world.

Why are orangutans so solitary?

Their food. Orangutans depend heavily on fruit, which in the Bornean rainforest is scattered, unpredictable, and often scarce — the forest goes through boom-and-bust "mast" cycles. A large ape cannot afford to share a patchy, low-calorie food supply with a group, so adult orangutans, especially females with young, mostly forage alone, holding a mental map of which trees fruit when. They still have a social network of loose, overlapping ranges and will gather at a big fruiting tree.

What are the flanges on a male orangutan's face?

Wide cheek pads of fatty tissue, backed by a throat sac used to produce a booming "long call." They develop only in dominant males, and their growth is socially suppressed — a subordinate male can stay in an unflanged, female-sized state for years and then develop flanges within months if the dominant male disappears. Flanged and unflanged males use different mating tactics — flanged males call and wait for females to come to them, while unflanged males range widely and force matings.

Why are orangutans endangered?

Overwhelmingly, habitat loss. Borneo's lowland rainforest has been cleared at one of the fastest rates on Earth for oil palm and pulpwood plantations, logging, and mining, and the remaining forest is fragmented by roads and estates. Orangutans are also killed when they raid plantation crops, and females are shot so their infants can be taken for the illegal pet trade. Fire, used to clear land, destroys huge areas of the peat-swamp forest they favour.