Guwahati: For decades, the railway tracks passing through Hollongapar Gibbon Sanctuary (HGS) in Jorhat district of Assam did more than just carry trains. It bisected the forest canopy, turning tree-lined highways into dead ends and dividing families of India’s only ape species, the western hoolock gibbon, inside their only home in the country.Hoolock gibbons live almost entirely above ground, moving through the upper canopy with brachiation – swinging by their arms in long, fluid arcs. Where the trees stop, their world stops. The railway corridor created a gap that they could not safely cross, leaving groups on either side isolated and a small section of families trapped away from the larger population.But the story changed on Friday when a male gibbon was recorded crossing newly installed canopy bridges with safety nets on the railway line, bringing a ray of hope not only to the apes but also to many other canopy-dwelling animals.The Wildlife Institute of India (WII) said, “This is the first confirmed use of a gibbon in the sanctuary – and the first documented use of a canopy bridge structure on a railway line anywhere in the world!”WII said that while this is a moment of pride for all stakeholders and a ray of hope to reduce the impact of linear infrastructure on India’s only ape species, careful infrastructure planning, eco-conscious settings and creating repurposed corridors to connect disparate populations is especially important for the long-term survival of threatened species like arboretums and gibbons.The bridges were designed and deployed during February–March 2025 on the single-track Lumding-Dibrugarh railway line, which has been passing through Hollongapar since 1887. In a technical report released in May 2023, WII said that the approximately 1.65 route-km ​​long broad-gauge, electrified single track divided the sanctuary into two unequal parts.Listed as Endangered on the IUCN Red List, the Western Hoolock Gibbon faces constant threats – shrinking forests, tea cultivation, human encroachment and illegal trade.The report said, “Over time, the sanctuary has become a ‘forest island’, disconnected from the surrounding forest areas. Since gibbons are exclusively arboreal animals living in the upper canopy of the forest, they are particularly sensitive to canopy gaps. Thus, the gibbon families on both sides of the railway track have effectively become isolated from each other, compromising their population genetic variability and their already intact population in the HGS. “The threatened existence has become more threatened.”The sanctuary is spread over an area of ​​20.98 km², consisting of tropical semi-evergreen type forests and is home to about 125 gibbons. Hoolock gibbons are primarily monogamous and live in small family groups of six closely related individuals.WII has highlighted how fragmented the gibbon population in the Hollongapar Sanctuary has become. About 26 family groups live within the sanctuary, but the railway line passing through it has divided the habitat into two unequal compartments. On the one hand, in very small, only four to five gibbon families remain. With no adequate canopy connectivity across the tracks, these families have been effectively isolated from the larger population on the other side for decades.The sanctuary also harbors wild mammals like the Bengal slow loris, the only nocturnal animal found in the northeast, stump-tailed macaques, northern pig-tailed macaques, eastern Assamese macaques, rhesus macaques and capped langurs, Malayan giant squirrels and parti-coloured flying squirrels, which depend on the dense canopy.Efforts to bridge the canopy gap had been made earlier also. In 2015, the railways built an artificial canopy bridge made of iron at a location across the railway track, but the structure was used by arboreal mammals, including gibbons, because many of its design aspects were not compatible with the gibbons’ specialized form of movement in the canopy, known as brachiation or swinging by the arms or forelimbs.Earlier in 2006, a natural canopy bridge was developed through long-term plantation activities on both sides of the railway track through the joint efforts of Aaranyak (a Guwahati-based conservation NGO) and the state forest department. WII reported that this natural canopy bridge was established and used only by gibbons until 2019, but this natural connectivity did not survive as the railway regularly cuts trees and branches as part of track maintenance activities.Union Environment Minister Bhupendra Yadav lauded the effort, calling it “technology-based conservation” and proof that “even small-scale science-based efforts can help greatly in biodiversity conservation.”“A happy moment from Holongapar. A year after installing the arboreal canopy bridge, the Hoolock gibbon is now using it to cross the railway track safely,” Assam CM Himnata Biswa Sarma said in a post on Instagram.