### Identification The Bornean Orangutan is a vision of shaggy, sunset-hued fur. Covered in coarse, mahogany-to-orange hair, they are the world’s largest arboreal mammals. Look for their remarkably long arms—reaching a span of over 2 meters—which dwarf their shorter legs. Adult males are unmistakable: they develop massive, fleshy cheek pads called flanges and a pendulous throat pouch used for resonating calls. Unlike their Sumatran cousins, Bornean orangutans have a bulkier build and darker, coarser coats. In the canopy, they appear as a slow-moving patch of red against the deep green of the dipterocarps.
### Habitat & Range Endemic to the island of Borneo, these "People of the Forest" are restricted to the remaining primary and secondary tropical rainforests. You’ll find them primarily in lowland dipterocarp forests and peat swamp forests, usually below 500 meters, though they occasionally venture up to 1,500 meters. They are most common in areas near riverbanks where fruit is abundant.
### Behaviour Observation requires patience; they are largely solitary and move with a deliberate, "slow-motion" grace. You’ll see them using their weight to sway trees, bridging gaps in the canopy. At dusk, listen for the rustle of arboreal engineering—they build a fresh sleeping nest of woven branches every single night. While females remain with their offspring for up to eight years, adult males are loners, announcing their presence with a "long call" that can be heard over a kilometer away through dense foliage.
### Diet Though they are primarily frugivores with a legendary craving for the pungent, spiked durian, their diet is incredibly diverse. They forage for over 300 types of fruit, but when the forest is lean, they pivot to eating inner tree bark, young leaves, and even mineral-rich soil. They use their dexterous fingers and powerful jaws to strip bark or extract seeds that other animals cannot reach.
### Fascinating Fact Bornean males exhibit a rare biological phenomenon called bimaturism. Some adult males do not develop cheek flanges, remaining small and "female-like" for years. This "stealth mode" allows them to live near a dominant flanged male without being attacked, waiting for the perfect moment to claim their own territory!