brachiators

Brachiation is a form of arboreal locomotion in which an animal moves by swinging from one forelimb to the next while its body is suspended beneath the limbs. It is most commonly associated with small to medium primates that live in tropical forests, and is distinct from other modes of movement such as knuckle-walking or all-fours climbing. In true brachiation, the animal’s weight is carried by the arms, and travel occurs through continuous arm-swinging between branches.

Anatomical adaptations that support brachiation include relatively long arms, a highly mobile shoulder girdle, and strong hands with curved digits for gripping branches. The wrist joints are capable of rotation and extension to permit overhead swings. Gibbons and siamangs, members of the family Hylobatidae, are the best-known true brachiators. They can perform rapid, long-distance swings with one or two arms, enabling efficient and agile movement through the forest canopy and reducing the need to descend to the forest floor.

Other primates may use arm-swinging or suspensory movements in certain contexts, but brachiation is not as specialized in orangutans, chimpanzees, or most monkeys. Those species typically rely on a combination of suspensory locomotion, climbing, or terrestrial movement depending on branch availability, body size, and ecological conditions. The evolution of brachiation is linked to forest structure that favors overhead travel between widely spaced supports, and it is most prominently exemplified by gibbons and their relatives.