However, they have been observed on the ground and in the highest branches of the trees. They eat leaves, fruit, insects and bird eggs. Proportions of arms and legs illustrate the specialization for brachiation. Shoulder joints also allow for flexible rotation of the shoulders and arms. A short body and legs make gibbons relatively light weight.
Gibbons are true brachiators.
That means they are able to arm swing through the trees. They also climb and leap. On the ground they walk bipedally with their arms held out to their sides. Their forearms are much longer than their hindlimb. When upright, Gibbons stand more erect than any other primate except for man.