EPOW - Ecology Picture of the Week

Hoolock Gibbon (Hylobates [Bunopithecus] hoolock)

Explanation:  We are deep in the South Garo Hills of the remote western part of the state of Meghalaya, northeast India.  Next to a small Garo village called Daribokgre is a sacred grove of tropical forest that is home to a very rare primate ... the forest man of South Asia, the hoolock gibbon. 

This is a tiny patch of mostly disturbed tropical mixed evergreen forest, less than 1 hectares (2.5 acres) in size, but surprisingly it still holds 3 or 4 hoolocks.  Pictured above is a mature female, who was carrying young, and elsewhere in the forest patch was the darker-colored male (to be presented in a future EPOW). 

Called heru by the local Garos, hoolocks range mostly in northeast India but also are found in adjacent corners of China, Myanmar (Burma), and Bangladesh.  They are the only great apes of India; they are not monkeys, so differ significantly from the macaques, langurs, and other primates of the region.  

Unlike monkeys, but like other species of gibbons found in southeast Asia, hoolocks have no tail and have remarkably long arms with hands specially adapted for brachiation -- that is, swinging through the tree canopy on branches and climbers, with astounding ease for so large a beast.  But they seldom move across the open ground, so when forests get cut, burned, and isolated, hoolock get stuck in these "lifeboat" forest patches.  

Hoolock are usually found in undisturbed interior areas of extensive, old tropical forests.  But how can so tiny a forest patch as this one hold a family?  

The answer may lie in two factors: their diet, and the local people.  Hoolock are mostly frugivorous and folivorous -- that is, they eat fruits and leaves -- and there is adequate diversity and density of their preferred foods in this forest patch to sustain them.  Also, people of the local Garo village not just tolerate the presence of this innocuous man of the forest, it is honored and, to a degree, revered ... as is this forest patch itself, which is viewed as a sacred grove and is not cut.  And also, hoolock form small, monogamous family groups with tight social bonds.  

Another nearby sacred grove, by the Garo village of Selbalgre, is 4 hectares (10 acres) in size and holds 10 hoolock.  This means that even these tiny forest patches, when protected and when preferred foliage food is present, can have densities of 2.5-4 hoolocks per hectare (1.0-1.6 hoolocks per acre), a surprisingly high density for so large a creature.  
  

Hoolock are listed as endangered and are the subject of important conservation projects.

 
Information:
     Alfred, J. R. B., and J. P. Sati. 1989. The gibbons with special reference to Hylobates hoolock. Pp. 384-390 in: T. C. Mujapuria, ed. Wildlife wealth of India. Tec Press Service, L.P., Bangkok, Thailand. 667 pp.
     Gupta, A. K. 2000. Primates of Tripura. Micro Mint, Dehra Dun. 40 pp.
     Menon, V. 2003. A field guide to Indian mammals. DK Delhi, London. 201 pp.
     Srivastava, A. 1999. Primates of northeast India. Megadiversity Press, Bikaner, Rajasthan, India. 208 pp.