Vanishing Species - Hoolock Gibbon

An Article by Mohan Pai

Hoolock Gibbon

Hoolock hoolock

Hoolock Gibbon is the only ape to be found in India and is a rare, highly endangered species.

Hoolock gibbon also known as white-browed gibbon, is the most accomplished acrobat of all the apes. A round face with a distinctive white band in place of eyebrows, long arms and absence of tail are the distinguishing features of this ape. Its flexible shoulder joints permit greater freedom of arms movement. Its long hands fasten on to branches like hooks. It seizes the branch with one hand, then it swings forward to grasp the next branch with the other hand, and in this way covers m in a single swing, almost literally skimming through the forest canopy at amazing speed. The most common position is hanging and sometimes swinging to and fro, referred to as ‘the crucifixion pose’.
The gibbon’s arms are very long, allowing the fingertips to touch the ground when the animal stands. On the ground the hoolock has a very characteristic gait. Its nose-bridge is more prominent than that of other apes. The gibbon would look quite human if it were not for the fairly heavy brow ridges and the low, sloping forehead.

Hoolock gibbon inhabits all the 7 states of northeast India from 100 to 1,370 m, and the northern, north- east and northwest limit of its range is the river Brahmaputra (Dibang in Arunachal Pradesh) which acts as a physical barrier for its distribution. It inhabits primary evergreen and less seasonal parts of semi-evergreen rainforests and rarely semi-deciduous forests. Habitat loss jeopardizes its survival and it is hunted in its entire range.

Hoolocks are the second largest of the gibbons, after the Siamang. They reach a size of 60 to 90 cm and weigh 6 to 9 kg. 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.The range of the hoolock extend from Assam in North-East India, to Myanmar. Small populations (in each case few hundred animals) live also in the eastern Bangladesh and in southwest China. Like the other gibbons, they are diurnal and arboreal, going through the trees with their long arms. They live together in monogamous pairs and 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 coat reaches its final coloration. Their life expectancy in the wild is about 25 years.

In India and Bangladesh its range is strongly associated with the occurrence of contiguous canopy, broad-leaved, wet evergreen and semi-evergreen forests. The species is an important seed disperser; its diet includes mostly ripe fruits, with some flowers, leaves and shoots. Western hoolock gibbons face numerous threats in the wild, and are now entirely dependent on human action for their survival. The debilitating threats include habitat encroachment to accommodate ever-growing human populations and immigration, forest clearance for tea cultivation, the practice of jhuming (slash-and-burn cultivation), hunting for food and “medicine”, capture for trade, and the degradation and decline in quality of their forests that impacts fruiting trees, canopy cover and the viability of their home ranges. Isolated populations face the additional threats arising from the intrinsic effects of small populations. Some populations surviving in just a few remaining trees are subjected to harassment by locals and to lack of food, and are attacked by dogs while attempting to cross clearings between forest patches.

Mostly hunted for food, it is also hunted for other purposes such as ornamentation, taboo, religious ceremonies, traditional medicine, etc. without any restriction.It is listed under Schedule I of the Wildlife (Protection) Act, 1972. IUCN SSC–Red Data Red Book records this species in the ‘Data deficient’ category.

Pic 1:Female Hoolock gibbon. Pic by: Dhritiman Mukherjee

Pic 2: "The Crusifixion Pose" by Ritu Raj Konwar

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