Hoolock gibbon  (Bunopithecus hoolock)

Hylobates means ‘dweller in trees' and, as one of the most agile animals of the forests, the gibbon certainly suited its old name (4). Though other apes have long limbs, mobile shoulders and are able to stand erect, gibbons have developed even greater propulsive abilities in their upper arms, and are able to cover three meters in a single swing (2) (4). This species is the second largest of the gibbons, and, like other members of the Hylobatidae family, males and females have different coat colours. Adult males have a completely black coat, while females are golden in colour, with darker brown cheeks (2). Both males and females have dark faces and, as their other common name (white-browed gibbon) suggests, bear white, curved brow streaks above the eyes. They also have longer body hair than other gibbons and, like all apes, lack tails (2). At birth, infants have a grey-white coat with a yellow tinge, which darkens as they mature (2).

It is not only appearances that distinguish gibbons in the forest. Their loud calls are unique and beautiful, with variations between species and even between sexes of a species. Male hoolocks emit two-phased calls that accelerate, while females reply with similar calls, but of a lower pitch (2) (5).

The hoolock gibbon occurs from eastern India (in the forests of Assam) to Bangladesh and southern China (6).

Inhabits tropical evergreen rainforest, semi-evergreen forests, tropical mixed deciduous forests and sub-tropical hill forests (6).

Gibbons exhibit a blend of characteristics that make them unique among primates. They are territorial, perform elaborate songs and display ‘suspensory behaviour'. They are also monogamous, and have a mainly frugivorous diet (2). Their most spectacular behaviour is probably their ability to travel easily through the canopy, 200 feet above the ground and at speeds of up to 35 mph (7). Gibbons do most of their travelling by swinging alternately from branch to branch and use their hands like hooks, often making long swings, in which neither arm supports them (brachiation) (4). Gibbons rarely descend to the ground, though when they do, they walk upright with the arms held high for balance (4).

The hoolock gibbon, like other gibbons, is active during the day, when it feeds on fruit, leaves, shoots, insects and birds' eggs (5). This species lives in small monogamous family groups of 2 - 5 individuals, which consist of a mated pair and their offspring (5). Territories extend for around 22 hectares and are defended fiercely by the adults, who chase intruders, display acrobatically and break branches to intimidate them (2) (5). The loud calls, often performed in duets, are also thought to contribute to the defence and establishment of territories, as well as being an essential communication tool in the dense forests (7).

Little is known about the reproductive behaviour of gibbons, though it is thought that hoolock gibbons bear offspring between November and March (4). Usually females give birth to single offspring, although twins have been recorded. There is an interbirth period of 2-3 years during which the mother cares for her young (4).

The main threat to this species is habitat destruction and fragmentation due to shifting cultivation, development of tea plantations and logging. Hunting is also a serious pressure on hoolock gibbon populations, as local people prize gibbon meat and bones for food and use in traditional medicine (4). There have been reports of intense hunting occurring in Assam in recent years, which is one of the main areas where the hoolock gibbon is found (6).

This rare and endangered primate does occur in the protected areas of Blaphakram and Namdapha National Parks in India. In other areas of its range the International Union for the Conservation of Nature and Natural Resources (IUCN) has recommended stronger legislation against hunting, and protection against deforestation in game reserves. Local environmental education has also been proposed as a method of raising awareness of the hoolock gibbon's listing as an endangered species (6). This primate is territorial and depends on large areas of forest for its survival. It is therefore imperative to protect large areas of forest from the pressures of human encroachment to allow this fantastic ape a chance of survival (7).

For more information on the hoolock gibbon and other gibbon species see:

Gibbon Conservation Centre:

http://www.gibboncenter.org

Gibbon Rehabilitation Project:

http://www.warthai.org/projects/grp.htm

Authenticated by Dr David J. Chivers, University of Cambridge.