The largest arboreal mammal is the orang-utan which lives in the canopy of tropical rainforests in Borneo and Sumatra. Bornean orang-utan (Pongo pygmaeus) and Sumatran orang-utan (P. abelii) males typically weigh 83 kg (183 lb) and measure 1.5 m (5 ft) tall. They have opposable toes on their feet and use their arm span of approximately 2 m (6 ft) to swing between branches and feed off fruit, small leaves and tree-bark. Being lighter (37 kg or 81 lb), the females usually build nests in the trees, whereas the adult males sleep on the ground.

The Malay word ‘orang-utan’ means ‘man of the forest’. There are believed to be 10,000-12,000 Bornean orang-utans in the wild, and even less of the critically endangered fellow sub-species the Sumatran orang-utan