Orangutan , anthropoid ape native to the forests of Borneo and Sumatra. The male adult attains a height of about 1.4 m (about 4.5 ft) and a weight of about 70 kg (about 150 lb), becoming corpulent with age. Twice the size of the female, the male has an air sac hanging down from its throat, which it inflates and uses to make the "long call," a throaty series of groans that can be heard up to a kilometer away by humans. Both the male and the female of the species have reddish-brown hair, which is luxuriant on the arms and thighs. Orangutans are almost exclusively arboreal, with limbs adapted to swinging through trees; the extremely long arms reach a span of about 2 m (about 7 ft), but the legs are short. The animals travel in small groups during the day, feeding on leaves and fruit, mainly figs. At night they nest in the forks of tall trees on individual platforms built of branches and leaves. Adult males generally live alone, and many groups are composed solely of females and young. Habitat destruction and hunting have made the orangutan an endangered species .