One of the true ‘acrobats of the forest’, the western hoolock gibbon (Hoolock hoolock) swings through the forest using its long arms, in a mode of locomotion known as brachiation. The western hoolock gibbon is, like the other 15 species of gibbon currently recognized, a slender and graceful ape. Adult male and female western hoolock gibbons are similar in size, but in the coloration of their dense hair they are vastly different. Adult males are black with a contrasting and distinctive white brow, giving them a highly expressive appearance. Females are copper-tan, with dark brown hair on the sides of the face and chest, and a distinct central parting in the head hair. Infants have grey-white hair with a yellow tinge at birth, which turns black with age. At puberty, the coat of females turns pale, whilst males remain unchanged. The gibbon is well known for its emotive call, which is mostly performed as a duet between a mated pair. Its call, both energetic and haunting, can be heard over long distances, and has seeped into the folklore of Asia’s indigenous people.