Context: The Hollongapar Gibbon Sanctuary has been split in two by a railway track running through it. The presence of the railway track splits the gibbons’ habitat and impedes their ability to move freely throughout the sanctuary area.

Canopy Bridge Proposal

• The proposal put out by the Wildlife Institute of India (WII) suggests the development of an artificial canopy bridge with the aim of enabling the migration of hoolock gibbons over the railway track located inside the sanctuary.
• The primary objective of this canopy bridge is to reestablish connectivity inside the fragmented habitat, facilitating unrestricted movement for the gibbons between the two distinct sections of the sanctuary.

Gibbon Habitat and Population

• The Hollongapar Gibbon Sanctuary, situated in the Jorhat region of Assam, has a total land area of 21 square kilometers.
• The sanctuary now houses around 125 hoolock gibbons, which represent the only ape species found in India.

Fragmentation and Threat to Habitat

• The article emphasizes that, similar to the other 19 gibbon species worldwide, the hoolock gibbons residing in this sanctuary are also facing the threat of endangerment as a result of habitat loss and fragmentation.
• The sanctuary has seen a loss of connectedness with the surrounding forest patches, resulting in the formation of a distinct ecological entity known as a “forest island.”
• Gibbons, being arboreal creatures that inhabit the top canopy of forested areas, exhibit sensitivity towards canopy gaps, hence making habitat fragmentation a matter of particular concern.

Gene isolation and survival

• The presence of the railway track has resulted in the segregation of gibbon families on each side, so reducing their genetic diversity.
• The genetic isolation of hoolock gibbons inside the sanctuary poses an additional risk to their survival, compounding the other vulnerabilities they currently face.

Hollongapar Gibbon Sanctuary

• The establishment of the Hollongapar Gibbon Sanctuary in 1997 was largely motivated by the objective of conserving the Hoolock Gibbon species and its natural environment.
• The Hollongapar Gibbon Sanctuary is located in the Jorhat district of Assam, in close proximity to the town of Mariani.
• The geographical extent of the region is roughly 20.98 square kilometers (8.11 square miles).
• The sanctuary exhibits distinct features of semi-evergreen and mixed deciduous forest, hence providing a wide array of habitats that support a broad variety of plant and animal species.

• Bio-diversity
  • The sanctuary is well recognized for its significant contribution to the preservation efforts of the Western Hoolock Gibbon (Hoolock hoolock), a species that has been classified as Endangered according to the IUCN Red List.
  • In addition to gibbons, the sanctuary accommodates a diverse array of primate species, such as the Stump-tailed Macaque and Capped Langur.
  • The avian richness in the area is notable, showcasing a wide array of bird species like the Great Hornbill, Green Imperial Pigeon, and White-cheeked Partridge.

• Vegetation
  • The sanctuary’s flora comprises of semi-evergreen and mixed deciduous woods, characterized by a diverse array of tree species such as Holong (Dipterocarpus macrocarpus), which lends its name to the sanctuary.
  • The presence of various forest types plays a crucial role in providing essential habitats for both permanent and migratory species.

Western Hoolock Gibbon

• Hoolock hoolock, a member of the family Hylobatidae, is a primate species that is widely recognized as gibbons in the scientific community.
• These organisms are distributed over several regions of South Asia, with a primary presence seen in India, Bangladesh, and Myanmar.
• The current estimated population size of hoolock gibbons is around 12,000 individuals.
• The Western Hoolock Gibbon is classified as one of the two distinct species of hoolock gibbons, with the other species being the Eastern Hoolock Gibbon (Hoolock leuconedys).
• Hoolock gibbons, classified as “lesser apes,” are little primates, distinct from the bigger “great apes” such as chimpanzees, gorillas, orangutans, and humans.
• The Western Hoolock Gibbons have a distinctive physical appearance characterized by a fur coat that is black or dark brown in color, accompanied by a white facial ring and prominent eyebrows.
• Both males and females exhibit comparable physical characteristics, however males tend to possess somewhat greater dimensions in comparison to females.
• Their elongated appendages are highly specialized for the locomotive behavior of brachiation, enabling them to proficiently traverse from one tree branch to another.
• Western Hoolock Gibbons inhabit many forest ecosystems, include tropical rainforests, subtropical woods, and mixed deciduous forests.
• These organisms reside inside the uppermost levels of the tree canopy and have a strong preference for arboreal habitats, with seldom terrestrial activity.
• The geographical distribution of the Western Hoolock Gibbon encompasses several regions in northeastern India, northern and western Myanmar (Burma), as well as southern China.
• The range of this species in India encompasses many states, including Assam, Arunachal Pradesh, and Nagaland.
• Gibbons are renowned for their noteworthy vocalizations, which serve as vital mechanisms for demarcating territory and fostering social unity among their groups. It is well recognized that they have the ability to generate musical compositions that possess the capacity to propagate audibly over considerable distances.
• The gibbons have a mostly frugivorous diet, including a diverse range of fruits, leaves, and sometimes, insects.
• The individuals live inside compact familial units including a monogamous dyad consisting of a male and female, with their progeny. Typically, these groups are comprised of two to four persons.
• The social organization of this species is centered on strong pair ties established between males and females, often engaging in duets as a component of their territorial conduct.
• The Western Hoolock Gibbon has been classified as an Endangered species according to the Red List of the International Union for Conservation of Nature (IUCN).
• According to the International Union for Conservation of Nature (IUCN) Red List, the Eastern Hoolock Gibbon is classified as Vulnerable.
• Both species are classified under Schedule 1 of the Indian (Wildlife) Protection Act 1972, therefore granting them the highest degree of legal protection in India.