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World Population of the Endangered Western Hoolock Gibbons Now Less than Previously Thought

Eastern Hoolock Gibbon Female
  Eastern hoolock gibbon female
(Hoolock leuconedys)

Rekha Chetry Ph.D and Dilip Chetry,Ph.D

The endangered western hoolock gibbon's (Hoolock hoolock) world population is now less than previously estimated. This lesser ape and close relative to man, known for its beautiful songs, was thought to be the only gibbon in Assam, India. Assam was thought to be one of the few places where it still had a viable population.

We surveyed six forest reserves in Sadiya, a part of Tinsukia district on the extreme east boundary of Assam. Instead of the western hoolock, we determined that the gibbon population is the vulnerable eastern gibbon (Hoolock leuconedys). A total of 33 individuals in 10 groups were recorded from direct sighting. We estimate the occurrence of another 16 groups from calls counted. The average group size was 3 with individuals ranging from 1 to 5. Sadly our survey found no gibbons present in 3 of the 6 forest reserves.

And these eastern hoolocks are under threat. The reserves, unlike a sanctuary or national park, do not enjoy strong legal protection and face numerous threats, including hunting, illegal logging, commercial harvesting of bamboo, cane, ferns, tora, and cattle grazing. Almost half of the forest reserve land is under encroachment with 6070 hectares out of 12,512 lost. This is due to a lack of community awareness and inadequate protection. The forest department has a staff of only 8 people to combat illegal activities and there are no staff quarters or offices in any of the reserves.

We initiated the first education and awareness program and our new findings received wide media coverage. We plan to recommend that the 3 reserve forests become wildlife sanctuaries with the eastern hoolock gibbon as a flagship species for conservation.

Rehka Chetry (wearing cap) with her survey team


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