Orangutan

About the orangutan

Orangutans are great apes native to the rainforests of Indonesia and Malaysia, now restricted to parts of Borneo and Sumatra, though during the Pleistocene their range extended across Southeast Asia and South China. Once considered a single species, they were split in 1996 into the Bornean orangutan (Pongo pygmaeus, with three subspecies) and the Sumatran orangutan (P. abelii); a third species, the Tapanuli orangutan (P. tapanuliensis), was confirmed in 2017. All three are the last surviving members of the subfamily Ponginae, which split from the lineage leading to gorillas, chimpanzees, and humans between 19.3 and 15.7 million years ago.

Orangutans show pronounced sexual dimorphism: females typically stand 115 cm (45 in) tall and weigh around 37 kg (82 lb), while males stand 137 cm (54 in) and weigh 75 kg (165 lb), with the tallest orangutan on record measuring 180 cm (71 in). Compared with humans they have proportionally long arms — a male's arm span runs about 2 m (6 ft 7 in) — and short legs. Long reddish hair, bright orange at first and darkening to maroon or chocolate with age, covers a body with grey-black skin underneath. Dominant adult males grow distinctive fatty cheek pads, or flanges, a prominent sagittal crest, extensive throat pouches used to amplify their long calls, and long canines; younger, subordinate males lack these features and look more like adult females. The hands have four long fingers and a notably short, opposable thumb, an arrangement that creates a secure hook grip for traveling through branches; the feet are similarly built, with an opposable big toe giving hand-like dexterity. Orangutans climb and swing through the canopy rather than knuckle-walking like African apes, instead walking on the sides of their hands and feet when they do come down to the ground, which is rarely — they are the most arboreal of the great apes and more cumbersome once on the ground.

Sumatran orangutans are more slender than their Bornean relatives, with paler, longer hair and a longer face, while Tapanuli orangutans have shaggier hair, smaller skulls, and flatter faces than either of the other two species, though they resemble Sumatran orangutans more closely overall.

Behavior and diet

Orangutans are mainly arboreal, favoring lowland dipterocarp forest and old secondary forest, with populations concentrated near rivers in freshwater and peat swamp forest; drier forest away from flooding and higher elevations both support fewer apes. They occasionally venture into grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes. A typical day starts with two to three hours of morning feeding, followed by a midday rest, afternoon travel, and the construction of a fresh sleeping nest from branches and foliage each night — a habit paired with sophisticated tool use that makes orangutans among the most intelligent primates studied. Field studies of the apes were pioneered by primatologist Biruté Galdikas, and there may be distinctive cultures within different populations. Tigers, clouded leopards, and wild dogs are potential predators, and captive orangutans can suffer upper respiratory tract disease.

Orangutans are the most solitary of the great apes, with social bonds forming mainly between mothers and their dependent offspring. Fruit dominates the diet, taking up 57 to 80% of foraging time even when scarce it still accounts for 16%, with soft-pulped fruits like figs, drupes, and berries favored; orangutans are the sole disperser of seeds for some plants, including the toxic vine Strychnos ignatii. Leaves make up roughly 25% of foraging time on average, eaten more heavily when fruit is scarce but still consumed 11 to 20% of the time even when it isn't. Orangutans round out their diet with bark, honey, bird eggs, insects, and small vertebrates such as slow lorises, and in some areas they practice geophagy, eating soil for its kaolin minerals — likely a way to counter the toxic tannins and phenolic acids in their plant diet.

Orangutans can live over 30 years in both the wild and captivity.

Range and habitat

Orangutans today survive only in parts of Borneo and Sumatra, a fraction of the range that once stretched across mainland Southeast Asia and South China during the Pleistocene. Bornean and Sumatran orangutans diverged as separate species, with the more recently described Tapanuli orangutan found in Sumatra south of Lake Toba. Within their remaining range, orangutans favor tropical rainforest, particularly lowland dipterocarp forest and old secondary forest, and are found in greater numbers near rivers, in freshwater and peat swamp forest, than in drier forest away from flood zones or at higher elevations. They will use grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes on occasion, but these are not primary habitat.

Conservation status

All three orangutan species — Bornean, Sumatran, and Tapanuli — are classified as Critically Endangered. Human activity is responsible for severe declines in both population and range. The species faces poaching, both for bushmeat and in retaliation for raiding crops, habitat destruction and deforestation driven by palm oil cultivation and logging, and the illegal pet trade. A number of conservation and rehabilitation organizations now work specifically to keep wild orangutan populations from disappearing further.