In the rain forests of Southeast Asia live the most agile of all mammals: the slender, long-limbed gibbons are remarkably agile brachiators. Their natural habitat is in the trees, where they can swing more than 3 m (10 ft.), moving from limb to limb with remarkable speed. They can leap farther than 9 m (almost 30 ft.). Sometimes, when moving along a large branch or on the ground, they stand upright with their arms held high for balance, like a tightrope walker. They sleep sitting up in the branches, huddled together in twos and threes.

There are eleven distinct species with much colour variation, ranging from creamy yellow to black. The weight of the different species ranges from 5 to 12 kg (13 to 26 lb.). Within a species, the male and female are about the same size.

Gibbons live in small family units, and claim a certain area of the forest as their territory. Each morning, before their daily search for fruits, leaves, and buds, and the occasional insect or young bird, they warn intruders of their presence by making ear-splitting shrieks that can be heard over long distances.

The continued health of the species is dependent on the survival of the rainforests. At the current rate of forest destruction it has been estimated that within 10 to 15 years half of the species could be extinct.