The forest habitat is one that the western hoolock gibbon is supremely adapted to. It swings effortlessly though the trees, reaching speeds of 56 kilometres per hour (4), and can also walk on two legs along branches that are too large to swing from, moving with impressive swiftness and balance (2). It feeds primarily on fruits, resulting in the western hoolock gibbon playing an important role as a seed disperser in the forest as the seeds are passed, undigested, in a new location (7). The gibbon’s simple stomach is well suited to this fruit-based diet which, unlike other primates, is limited in its ability to digest leaf material (5), although the western hoolock gibbon does consume some flowers, leaves and shoots (8).
Like other species of gibbon, male and female western hoolock gibbons form monogamous pairs that may remain together for many years. However, this faithfulness is not absolute, as both members of the pair may mate with other individuals (4). Each pair, along with any immature offspring they have, occupy a territory that is defended with both vocal and visual displays (4). The female gives birth every two and a half to three years to a single infant, which will remain in the family group for seven to ten years. Upon reaching maturity, the parent of the same sex will act aggressively towards the offspring until they leave the group (4).