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Text and photos by Nick Baker, unless credited to others.
Copyright © Ecology Asia 2025

 
     
 

 

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

   
   
 
Western Hoolock 
Hoolock hoolock
   
   

Order : PRIMATES
Family : Hylobatidae
Species : Hoolock hoolock

Head-body length : up to approx. 65 cm
Tail length : no tail
Weight : up to approx. 9 kg?

Play call

Hoolock hoolock (Western Hoolock Gibbon) is one of three species in the Hoolock genus. It is listed as Endangered by IUCN (Brockelman et al, 2019).

This primate occurs in eastern Bangladesh, northeastern India (Assam) and northwestern Myanmar (west of the Chindwin River, a tributary of the Irrawaddy River (Ayerawady)). 

To the east of the Chindwin River it is replaced by the Gaoligong Hoolock (Hoolock tianxing) and the Eastern Hoolock (Hoolock leuconedys). 

Myanmar may prove to support the most viable populations of Hoolock hoolock, but there is little ongoing research (Brockelman et al, 2019).

Hoolock gibbons are larger than those of the widespread genus Hylobates. Their weight is only significantly exceeded by the Siamang (Symphalangus syndactylus).

Adult males are black with white
eyebrows, and sometimes with white on the chin. Adult females are creamy brown with darker cheeks, and a white face ring. Infants are born all white (Francis, 2019).

As with all gibbons, this primate is strongly arboreal, but some may briefly come to the ground to move from one group of trees to another. Their diet comprises forest fruits, supplemented by leaves, buds and occasional protein-rich insects (Francis, 2019).

Their calls are less complex than those of other gibbon genera, and there is an absence of the whooping and high notes of Hylobates, for example. Male and female calls appear to be similar; both sexes possess a laryngeal sac (Francis, 2019). 

Hoolock hoolock inhabits a range of forest types including tropical evergreen forest, semi-evergreen forest, tropical mixed deciduous forest and subtropical broadleaf hill forest, as well as bamboo-dominated areas, up to elevations of 2500 metres.

Populations of this primate are threatened by the continuing loss of their forest habitat as well as hunting for the bush meat trade. Infants are also captured for the local pet trade.


Fig 1 : Adult female at Lawachara National Park, Bangladesh.  Photo thanks to AKM Emdadul Islam Bitu.

Fig 2 :
Adult male at Hollongapar Gibbon Sanctuary, Assam, India.  Photo thanks to Miraj Hussain.


References : 

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

Francis, C.M. 2019. A Field Guide to the Mammals of South-east Asia. Second Edition. New Holland. 416 pp.


Acknowledgments : Audio file courtesy Yong Ding Li.

Fig 1
 
©  AKM Emdadul Islam Bitu

Fig 2
 

 ©  Miraj Hussain


Fig 1 by AKM Emdadul Islam Bitu and Fig 2 by Miraj Hussain are both licensed under the Creative Commons Attribution Share Alike 4.0 International license.