Hoolock Gibbon Species in India

Western Hoolock Gibbon

Western Hoolock Gibbon Faces Threat of Extinction 

-Dr. Arvind Singh 

Western hoolock gibbon is a species of primate found in India and neighbouring countries of Bangladesh and Myanmar. The scientific name of the Western hoolock gibbon is Hoolock hoolock and it belongs to Hylobatidae family of order Primates. It is one of the two species of apes found in India. The other species of ape found in India is Eastern hoolock gibbon scientifically known as Hoolock leuconedys. The latter is also found in Northeast India.

Due to drastic reduction in population the Western hoolock gibbon is listed as ‘Endangered’ in the Red List of Threatened Species of International Union for Conservation of Nature and Natural Resources (IUCN). Endangered species are those species which are facing threat of extinction in near future.

Distribution Range:

The Western hoolock gibbon is found in all the states of Northeast India restricted between the south of Brahmaputra River and east of Dibang River. The range of Western hoolock gibbon in Northeast India extends into seven states covering, Assam, Arunachal Pradesh, Manipur, Meghalaya, Mizoram, Nagaland and Tripura. Outside India it is found in Eastern Bangladesh, Northwest Myanmar and probably in Southeastern Tibet.

According to an estimate, over the last 3 to 4 decades the numbers of Western hoolock gibbon have dropped from more than 100,000 to less than 5,000 individuals. In 2009 it was considered as one of the 25 most endangered species of primates.

Physical Characteristics:

Western hoolock gibbon reaches a size of 60-90 cm and weighs between 6 to 9 kg. Both sexes are of the same size, however, they differ in the colouration of their dense hair. The males are black coloured with remarkable white brows while females have a grey-brown fur, which is darker at the chest and neck. White rings around their eyes and mouths give their faces a mask-like appearance.
At puberty, the coat of female turns pale whilst males remains unchanged.

Habitat and Ecology:

The Western hoolock gibbon inhabits tropical evergreen rain forests, tropical evergreen and semi-evergreen forests, tropical mixed deciduous forests and sub-tropical broadleaf hill forests. This primate species may also be seen moving through or sleeping in bamboo forest and plantations of Terminalia myriocarpa and Lagerstroemia flos-reginae. Its preferred habitat, however, is dense evergreen and semi-evergreen forests.

Western hoolock gibbon is diurnal and arboreal. It swings through the forest using it long arms in a mode of locomotion known as brachiation. It can brachiate at speeds up to 55 km/ hour covering up to six meters in just one swing.

The Western hoolock gibbon is a frugivorous species with ripe fruits constituting a majority of its diet. Its simple stomach is well suited to a fruit-based diet which unlike other primates, is limited in its ability to digest leaf material. Nevertheless, the Western hoolock gibbon does consume some flowers, leaves and shoots. The species is an important seed disperser.

Western hoolock gibbon form monogamous pairs that remain together for years, though mating outside the pair has been noticed in some individuals. It is known for the emotive call that echoes across long distances in the forest and is used by individuals to attract males.

Females give birth to one offspring every 2 to 3 years. The gestation period is of seven months. The young’s of Western hoolock gibbon is born with milky white or buff-coloured hair. After about six months the hair of males darkens and turns black while the female hair remains buff-coloured throughout life. They are fully mature after 8 to 9 months. The life expectancy in the wild is about 25 years.

Threats to Survival:

The population of Western hoolock gibbons have declined by almost 90% over the last three decades and is now considered to be one of the most endangered primate species in the world.

The main threats to the survival of Western hoolock gibbon include habitat loss, habitat fragmentation, hunting and capture for trade.

Habitat loss and fragmentation are basically due to clearing of forests for tea cultivation, jhum cultivation (slash and burn agriculture), logging, harvesting of bamboo for paper mills, oil mining and exploration, and coal mining.

When forests are fragmented, the gibbons spend more time on the ground, moving between forest patches. At these moments, they become vulnerable to domestic and wild dogs.

People hunt this primate species for food and traditional medicine. The gibbon’s beautiful songs act as signal that guides hunters directly to them.


Western hoolock gibbon is listed on Schedule I of the Indian Wildlife (Protection) Act, 1972. The Government of Assam upgraded the status of Hoollongapar Reserve Forest in the Jorhat District of Assam to a Gibbon Wildlife Sanctuary in 1997 for the conservation of both Western hoolock gibbon and Eastern hoolock gibbon.

Word Wide Fund for Nature-India (WWF-India) works in the state of Assam and Arunachal Pradesh is Northeast India with a holistic conservation approach towards protecting flagship species like tigers, rhinoceros and elephants. The hoolock gibbons (Western hoolock gibbon and Eastern hoolock gibbon) are indirectly benefitted from WWF-India conservation initiatives in their distribution range. The following actions must be brought in practice for the conservation of Western hoolock gibbons in India.

1. To regularly monitor the population of Western hoolock gibbon in their distribution range. 

2. To strictly enforce the Wildlife (Protection) Act. 

3. To check the habitat loss of Western hoolock gibbon. 

4. To restore the degraded habitats of Western hoolock gibbon. 

5. To put complete ban on shifting cultivation (Jhum cultivation) in distribution range of Western hoolock gibbon. 

6. To promote captive breeding and subsequent release in their natural habitats. 

7. To educate the people about the biological significance of this primate species. 


It can be concluded that Western hoolock gibbon is an important species of primate facing threat of extinction in wild mainly due to habitat loss, habitat fragmentation and hunting. Therefore, conservation of this primate species is the need of the hour for maintenance of biodiversity and environmental stability.
Dr. Arvind Singh is M. Sc. and Ph. D. in Botany with an area of specialization in Ecology. He is a dedicated Researcher having more than four dozen published Research Papers in the Journals of National and International repute. His main area of Research is Restoration of Mined Lands. However, he has also conducted Research on the Vascular Flora of Banaras Hindu University-Main Campus, India.

keywords: hoolock gibbon iucn, hoolock gibbons, western hoolock gibbon, hoolock gibbon in india, hoollongapar gibbon sanctuary, hoolock gibbon ape, hoolock gibbon species found in india, gibbon wildlife sanctuary, hoolock gibbon species in india, hoolock gibbon india, eastern hoolock gibbon