IAS Gyan

Daily News Analysis


30th August, 2023 Environment

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  • A railway track has divided the Hollongapar Gibbon Sanctuary. This division created by the railway track disrupts the habitat and movement of the gibbons within the sanctuary.


Canopy Bridge Proposal

  • The Wildlife Institute of India (WII) proposed designing an artificial canopy bridge to facilitate the movement of hoolock gibbons across the railway track within the sanctuary.
  • This canopy bridge aims to reconnect the divided habitat and enable the gibbons to move freely between the two parts of the sanctuary.

Habitat and Gibbon Population

  • The Hollongapar Gibbon Sanctuary, located in the Jorhat district of Assam, covers an area of 21 sq. km.
  • The sanctuary is home to about 125 hoolock gibbons, which are India's only ape species.

Habitat Fragmentation and Endangerment

  • The report highlights that like the other 19 gibbon species globally, the hoolock gibbons in this sanctuary are also endangered due to habitat loss and fragmentation.
  • The sanctuary has lost connectivity with surrounding forest patches, creating a "forest island."
  • Gibbons, being arboreal animals living in the upper canopy of the forest, are sensitive to canopy gaps, making habitat fragmentation especially concerning.

Genetic Isolation and Survival Concerns

  • The division caused by the railway track has isolated gibbon families on both sides, compromising their genetic variability.
  • This genetic isolation further endangers the survival of the hoolock gibbons within the sanctuary, which were already facing threats to their existence.

Hollongapar Gibbon Sanctuary: A Comprehensive Overview

Location and Geography

  • Hollongapar Gibbon Sanctuary was established in 1997 primarily for the conservation of the Hoolock Gibbon and its habitat.
  • Hollongapar Gibbon Sanctuary is situated in the Jorhat district of Assam, near the town of Mariani.
  • It covers an area of approximately 20.98 square kilometers (8.11 square miles).
  • The sanctuary is characterized by semi-evergreen and mixed deciduous forests, offering a diverse range of habitats for various flora and fauna.


  • The sanctuary is renowned for its role in the conservation of the Western Hoolock Gibbon (Hoolock hoolock), which is listed as Endangered on the IUCN Red List.
  • Apart from gibbons, the sanctuary is home to various other primate species, including the Stump-tailed Macaque and Capped Langur.
  • The avian diversity is also significant, with a variety of bird species such as the Great Hornbill, Green Imperial Pigeon, and White-cheeked Partridge.


  • The sanctuary's vegetation includes semi-evergreen and mixed deciduous forests, with a range of tree species like Holong (Dipterocarpus macrocarpus) from which the sanctuary gets its name.
  • The diverse forest types provide important habitats for the resident and migratory species.

About Western Hoolock Gibbon

  • Hoolock hoolock is a primate species belonging to the family Hylobatidae, commonly known as gibbons.
  • They are found in parts of South Asia, primarily in India, Bangladesh, and Myanmar.
  • The estimated current population of hoolock gibbons is around 12,000 individuals.

Taxonomy and Classification

  • The Western Hoolock Gibbon is one of the two species of hoolock gibbons, the other being the Eastern Hoolock Gibbon (Hoolock leuconedys).
  • Hoolock gibbons are small apes and are often referred to as "lesser apes," in contrast to the larger "great apes" like chimpanzees, gorillas, orangutans, and humans.

Physical Characteristics

  • Western Hoolock Gibbons have a distinct appearance with a black or dark brown fur coat, with a white face ring and pronounced eyebrows.
  • Males and females have similar appearances, but males are slightly larger than females.
  • They have long arms, which are well adapted for brachiation (swinging from branch to branch) through the trees.


  • Western Hoolock Gibbons are found in a variety of forest types including tropical rainforests, subtropical forests, and mixed deciduous forests.
  • They inhabit the upper canopy layers of trees and are highly arboreal, rarely descending to the ground.

Geographical Distribution

  • The Western Hoolock Gibbon's range extends across parts of northeastern India, northern and western Myanmar (Burma), and southwestern China.
  • In India, their distribution spans states like Assam, Arunachal Pradesh, and Nagaland.

Behavior and Ecology

  • Gibbons are known for their impressive vocalizations, which play a crucial role in marking territory and maintaining group cohesion. They are known to produce songs that can be heard over long distances.
  • These gibbons are primarily frugivorous, feeding on a variety of fruits, leaves, and occasionally insects.
  • They live in small family groups consisting of a monogamous pair (male and female) and their offspring. These groups usually consist of two to four individuals.
  • Their social structure revolves around strong pair bonds between males and females, who often perform duets as part of their territorial behavior.

Conservation Status

  • The Western Hoolock Gibbon is listed as Endangered on the International Union for Conservation of Nature's (IUCN) Red List.
  • The Eastern Hoolock Gibbon is listed as Vulnerable on the IUCN Red List.
  • Both species are listed on Schedule 1 of the Indian (Wildlife) Protection Act 1972, which offers them the highest level of legal protection in India.



The report underscores the urgent need to address the impact of the railway track division on gibbon populations and genetic diversity. The proposed canopy bridge solution could potentially mitigate the negative effects of habitat fragmentation and improve the chances of survival for the hoolock gibbons.


Q. Which of the following statements about the Western Hoolock Gibbon is true?

a) It is the largest species of gibbon.

b) It is found in the tropical rainforests of South America.

c) It is not at risk of extinction due to its adaptability.

d) It has a prehensile tail used for grasping branches.

Correct answer: a)