Meet The Species
The Bornean Orangutan: Borneo's Endangered Great Ape
What sets the Bornean orangutan apart from its Sumatran cousin, why it's ranked critically endangered, and what that means for the animals you see at Sepilok.
See Sepilok tours on Viator ↗A great ape found nowhere else
The orangutan at Sepilok is the Bornean orangutan, Pongo pygmaeus, one of only three orangutan species, found only on the island of Borneo. It's a large, mostly solitary, tree-dwelling ape with distinctive reddish-brown hair and arms that can span roughly twice its body length — built for swinging through the rainforest canopy rather than walking on the ground. Adult males develop wide cheek pads and a throat pouch used for long, carrying calls that travel through the forest. Conservation assessments put the total wild population well under a hundred thousand and still falling, spread across shrinking, increasingly fragmented pockets of forest in Sabah, Sarawak and Indonesian Kalimantan.
Why it's ranked critically endangered
The IUCN lists the Bornean orangutan as Critically Endangered, its most serious category short of extinction in the wild. The core problem is habitat: decades of logging and conversion of rainforest to oil palm and other plantations have shrunk and fragmented the forest orangutans need, while hunting and the illegal pet trade add further losses. Orangutans also reproduce unusually slowly — females typically have a single infant roughly once every six to eight years, one of the longest birth intervals of any mammal — so populations recover very slowly from losses. That combination of habitat loss and slow reproduction is why a centre like Sepilok, focused on giving orphaned individuals a route back to the forest, matters.
How it differs from Sumatra's orangutan
Borneo and Sumatra each have their own orangutan species, and Sumatra's forests also hold the more recently identified Tapanuli orangutan. The Bornean orangutan is generally stockier and darker-coated than its Sumatran relative, and spends somewhat more time moving on the ground — partly because Borneo, unlike Sumatra, has no tigers, so there's less pressure to stay in the canopy. The two main species also differ in social behaviour and diet in subtle ways studied by primatologists. None of this affects how a Sepilok visit works, but it's worth knowing that the animals here are a genetically distinct population found only on this island, not a generic 'orangutan' you'd see anywhere in Southeast Asia.
What orangutans actually eat, and where they sleep
Wild fruit makes up the bulk of a Bornean orangutan's diet — figs and other rainforest fruit in particular — topped up with young leaves, bark, insects, and occasionally honey or bird eggs when fruit is scarce. That flexibility matters, because Bornean forests don't fruit on a steady schedule; irregular 'masting' events see many tree species fruit heavily all at once, followed by long lean stretches. Orangutans also build a fresh sleeping nest almost every night, weaving branches and leaves into a platform high in the canopy in a matter of minutes — a skill young orangutans have to learn from their mothers rather than one they're born knowing, which is part of why orphaned infants need so much relearning in care.
Flanged males, and a life spent in the trees
Not every adult male orangutan develops the wide cheek pads, or flanges, and throat pouch you might picture — only dominant 'flanged' males do, using the pouch to produce long calls that carry through the forest and warn off rivals. Other adult males stay 'unflanged', resembling females for years, sometimes their whole lives, a genuine and still not fully understood variation rather than a stage every male passes through. Whichever form they take, Bornean orangutans are the most arboreal of the great apes, spending the overwhelming majority of their time moving through the canopy on those long, powerful arms rather than on the ground — which is exactly why the reserve's forest, not any enclosure, is what makes their rehabilitation possible.