Hoolock hoolock | Western Hoolock Gibbon

 

Good spot: Lawachara National Park, Bangladesh

Western Hoolock Gibbon_Sabit Hasan

A hanging Western Hoolock Gibbon

© Sabit Hasan

 

Primatology

 

Taxonomy & Occurrence

Hoolock hoolock is a monotypic species (no subspecies). This species was first described from the Garo Hills of Assam state of India [1]. It ranges from northeastern India (south of Brahmaputra and Nao-Dehing Rivers) to northwestern Myanmar (west of the Chindwin River) through eastern Bangladesh [2,3]. A population in southeastern Tibet of China just across the border with Arunachal Pradesh state of India is thought to be Hoolock hoolock but its identity has not been established [2].

 

Based on morphological characteristics using photographs and direct observations, hoolock gibbon populations in between the Dibang, Lohit, and Nao-Dehing rivers in northeastern India were reported as a subspecies called the Mishmi Hills Hoolock Gibbon (H. hoolock mishmiensis), but the same populations were also reported as the Eastern Hoolock Gibbon (H. leuconedys) [2,3]. A recent phylogenetic analysis discarded both claims [3]. Hence, Hoolock hoolock is the only gibbon species not only in India but also in South Asia.

Hoolock hoolock map.jpg

Distribution of Western Hoolock Gibbons 

© Brockelman et al. 2019 [2]

 

IUCN Conservation Status

Endangered

The Western Hoolock Gibbon populations are facing tremendous anthropogenic pressures from habitat loss, fragmentation, hunting, electrocution, and illegal harvesting for pet trade and local zoos [2]. About 400 individuals of the Western Hoolock Gibbons were estimated to occur in the fragmented forests in the Sylhet and Chittagong divisions of eastern Bangladesh, while several local extinctions were documented in southeastern Bangladesh [4]. The total population of the species in Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura states of India was reported to be over 12,000 individuals [2]. It is believed that Myanmar has the largest population of Western Hoolock Gibbons but no estimates are available yet [2].

 

Seeing this Species

Just like other gibbons (Hylobates, Nomascus, Symphalangus), the Western Hoolock Gibbon can be heard from kilometres away. The gibbons regularly call in the early mornings, so be sure to be up and out by 7am! In Bangladesh, the Western Hoolock Gibbon can be found in 12 protected forests and several reserve forests [4].

Lawachara National Park, Bangladesh

Lawachara National Park is located in Kamalganj Upazila, Moulvibazar District in the northeastern region of Bangladesh. It is about 160 km northeast of the capital Dhaka and 60 km from Sylhet bordering the Indian states of Assam and Tripura. The nearest town, Sremangal is only 8 km from the Lawachara National Park. Lawachara National Park is part of the West-Bhanugach Reserve Forest, and covers an area of 12.5 square km of mixed evergreen forests. A road and a railway traversed the forests, and two villages of the Khasia ethnic group live inside the National Park. Numerous sandy-bedded streams crisscrossed the forests. 

The National Park is one of the remaining strongholds of many globally threatened primates, small mammals, reptiles, amphibians, birds and butterflies in Bangladesh. Here, there are about 40 individuals of Western Hoolock Gibbons and about 130 individuals of Phayre’s Langurs [4,5].

Probability of success:  ◆ ◆ ◆ ◇ ◇

 

Overlapping species:

  • Northern Pig-tailed Macaque (Macaca leonina)

  • Rhesus Macaque (Macaca mulatta)

  • Bengal Slow Loris (Nycticebus bengalensis)

  • Phayre's Langur (Trachypithecus phayrei)

  • Capped Langur (Trachypithecus pileatus)

Other sites:

Patharia Hill Reserve Forest, Bangladesh

Patharia Hill Reserve Forest in northeastern Bangladesh supports a good population of about 25 groups of Western Hoolock Gibbons [4]. This 8,019 ha forest is situated at the Barlekha Upazila of Moulvibazar District under the Sylhet Division. It is about 250 km away from the capital city of Dhaka and 60 km from the nearest small town called Juri. The reserve forest is a part of a large continuous forest (including plantations) bordering the Assam state of India. It has diverse topographic features including hilly areas and grasslands. This mixed evergreen, stream-fed forest harbours at least 26 globally threatened wildlife species including seven species of primates.

With permission of the local forest department and border guards Bangladesh, tourists can visit the forests accompanying local eco-tourist guides. There are accessible hilly forest trails and streams to walk into the forest and to watch the wildlife in the morning.

 

Overlapping species:

  • Western Assamese Macaque (Macaca assamensis pelops)

  • Northern Pig-tailed Macaque (Macaca leonina)

  • Rhesus Macaque (Macaca mulatta)

  • Bengal Slow Loris (Nycticebus bengalensis)

  • Phayre's Langur (Trachypithecus phayrei)

  • Capped Langur (Trachypithecus pileatus)

 

Atota Hill Reserve Forest, Bangladesh

Inani Reserve Forest, Bangladesh

Kaptai National Park, Bangladesh

Kasalong Reserve Forest, Bangladesh

Rajkandhi Reserve Forest, Bangladesh

Rema-Kalenga Wildlife Sanctuary, Bangladesh

Sangu-Matamuhuri Reserve Forest, Bangladesh

Satchari National Park, Bangladesh

Namdapha National Park, India

Trishna Wildlife Sanctuary, India

Mann River Wildlife Sanctuary, Myanmar

Local contacts: Sabit Hasan (Bangladesh Hoolock Gibbon Project); Tanvir Ahmed (Phayre's Langur Conservation Initiative in Bangladesh)

Trachypithecus phayrei in Rajkandhi Reserve Forest, Bangladesh_Tanvir Ahmed.jpg
Hoolock hoolock_3_Sabit Hasan.JPG

A pair of Western Hoolock Gibbons (male on the left; female right)

© Sabit Hasan

Lawachara National Park, northeast Bangladesh

Primate watching

© Tanvir Ahmed

Rajkandhi Reserve Forest, northeast Bangladesh

References

[1] Harlan R. & Burrough M., 1834. Description of a species of Orang from the North-Eastern Province of British East India, lately the Kingdom of Assam. Transactions of the American Philosophical Society 4, 52–59.

[2] Brockelman W, Molur S. & Geissmann T., 2019. Hoolock hoolock. The IUCN Red List of Threatened Species 2019: e.T39876A17968083.

[3] Trivedi M., Manu S., Balakrishnan S., Biswas J., Asharaf N.V.K. & Umapathy G., 2021. Understanding the phylogenetics of Indian hoolock gibbons: Hoolock hoolock and H. leuconedys. International Journal of Primatology 42(3), 463–477.

[4] Naher H., Al-Razi H., Ahmed T., Hasan S., Jaradat A. & Muzaffar S., 2021. Estimated density, population size and distribution of the endangered western hoolock gibbon (Hoolock hoolock) in forest remnants in Bangladesh. Diversity 13(10), 490.

[5] Ahmed T., Hasan S., Nath S. & Biswas S., 2020. Population status of Phayre’s langur in north-eastern forests of Bangladesh. 7th Asian Primate Symposium and 1st International Conference on Human Primate Interface, Guwahati, Assam, India.

 

Contributed by Sabit Hasan and Tanvir Ahmed

Page last updated: 25 September 2022