Guwahati: A simple set of overhead canopy bridges has delivered a major conservation win in western Assam, cutting road accidents involving the endangered golden langur by nearly three-quarters along a busy state highway, according to a new scientific study.
The research, published in the December 2025 issue of the Journal of Wildlife Science, shows that artificial canopy crossings installed above a 5.2-km stretch of State Highway-14 in Kokrajhar district reduced vehicle collisions with golden langurs by about 74 per cent.
The findings underscore how low-cost, wildlife-sensitive infrastructure can make a decisive difference in landscapes fractured by roads and development.
Golden langurs are strictly tree-dwelling primates found only along the Indo-Bhutan border. In Assam, their southern populations, particularly in Kokrajhar and neighbouring Bongaigaon, are hemmed into small forest islands carved up by farms, settlements, roads, and power lines. These fragmented patches are estimated to hold roughly a quarter of India’s remaining golden langur population.
Such fragmentation has deadly consequences. When forest canopies are broken by roads, arboreal animals are forced to descend to the ground to cross, placing them directly in the path of fast-moving traffic.
To address this risk, a team of primatologists and wildlife biologists led by Jihosuo Biswas and Joydeep Shil installed 15 artificial canopy bridges at known animal crossing points along the highway.
The structures included pipe bridges, ladder bridges, rope bridges, and hybrid designs, each suspended above the road to reconnect severed tree canopies.
Before the intervention, between January 2023 and December 2024, researchers documented 18 vehicle collisions involving golden langurs on the same road stretch, killing seven animals and seriously injuring several others.
After the bridges were put in place, monitoring revealed swift behavioural change. Of 112 recorded road crossings by golden langurs, nearly 74 per cent were made using the canopy bridges. Pipe bridges emerged as the most frequently used design. Crucially, ground-level crossings, where the risk of fatal collisions is highest, fell sharply.
The stakes are particularly high in Kokrajhar, which alone supports an estimated 15 per cent of India’s golden langur population. “Targeted mitigation in such strongholds can have an outsized impact on species survival,” the study notes.
However, the authors caution that canopy bridges are not a silver bullet. Golden langurs in Assam also face threats from electrocution on uninsulated power lines, vehicle speed, habitat degradation, and long-term genetic isolation.
The study recommends pairing canopy crossings with measures such as power-line insulation, traffic calming, habitat restoration, and the protection of forest corridors.
Community participation is also highlighted as critical. Local involvement in monitoring bridge use, maintaining warning signage, and restoring canopy links can significantly improve the effectiveness and longevity of such interventions.
As Northeast India undergoes rapid infrastructure expansion, the study adds to growing global evidence that thoughtfully designed, species-specific solutions, like canopy bridges, can reconcile development with the survival needs of some of the region’s most vulnerable wildlife.