The Hoolock Gibbons, (Hoolock), are two primate species from the family of gibbons (Hylobatidae). The range of the hoolocks is the most northwestern of all the gibbons, extending from Assam in North-East India, to Myanmar. Small populations live also in eastern Bangladesh and in southwest China.
Hoolocks are the second largest of the gibbons, after the Siamang. They reach a size of 24 to 36 inches and weigh 13.22 to 20 pounds. The genders are about the same size, but they differ considerably in coloration. Males are black colored with remarkable white brows, while females have a grey-brown fur, which is darker at the chest and neck. White rings around the eyes and around the mouth give their face a mask-like appearance.
Like the other gibbons, they are diurnal and arboreal, brachiating through the trees with their long arms. They live together in monogamous pairs, which stake out a territory. Their calls serve to locate family members and ward off other gibbons from their territory. Their diet consists mainly of fruits, insects and leaves.
Young hoolocks are born after a seven month gestation, with a milky white fur. After about six months their fur turns black. After 8 to 9 years they are fully mature and their fur reaches its final coloration. Their life expectancy in the wild is about 25 years.