They are predominantly frugivores, but have also been observed eating leaves, bark and bird eggs. Orangutans are cautious climbers, and are mainly arboreal. In the trees they move by grasping slender branches and climbing. They are usually cautious in grabbing branches with two or three arms or legs. On the ground they walk quadrupedally, using the lateral side of the palms.
Orangutans are extremely flexible in the hip, knee, and shoulder joint.
Their forearms are much longer than their hindlegs. They are diurnal. One male may have a territory that covers the range of several females. Females are found by themselves, unless they have a young child. During his constant movement within his territory, the male will know when a female is sexually receptive by the type of calls she makes.