The orangutan's legs are relatively short and weaker than the arms. Males are much larger and heavier than females and are also identified by the cheek flaps that surround the face of the mature adult.
All adults have fatty throat pouches.
Orangutans live alone, in pairs or in small family groups and are active in the daytime at all levels of the trees. They walk along large branches on all fours or erect and sometimes swing by their hands from branch to branch. On the ground, they walk on all fours or stand erect. Fruit is their staple diet, but they also feed on leaves, seeds, young birds and eggs. After a gestation period of more than 9 months, the female gives birth to a single young.