Saving Assam's Golden Langurs through innovation and community efforts

The golden langur, a canopy-dwelling primate native to the Indo-Bhutan border, faces an uncertain future due to rapid habitat destruction. Found primarily in four districts of Assam and six in Bhutan, this striking species is battling for survival as its forest habitat continues to disappear. 

Nowhere is this crisis more pronounced than in the southern part of Assam’s Kokrajhar and Bongaigaon districts, where deforestation, infrastructure development, and human encroachment are shrinking the golden langur’s home range. The increasing fragmentation of forests is driving these primates to adapt to new dangers, including crossing roads and surviving in isolated forest patches, which expose them to fatal threats such as road accidents and electrocutions.

Golden langurs are exclusively arboreal, depending on interconnected forest canopies for movement and survival. Unfortunately, over half of their habitat has been lost in India, primarily due to deforestation, forest conversion into farmlands, and urban expansion. 

Dr. Jihosuo Biswas, a senior primatologist at the Primate Research Centre in Northeast India, highlights that this ongoing deforestation has caused the once-thriving forests to fragment into smaller patches, severely endangering the langur population.

"Linear infrastructure developments, such as roads and settlements, have isolated these patches, forcing golden langurs into terrestrial behaviors—something they’re not evolved to do," explains Dr. Biswas. The resulting fragmentation poses immense risks to the golden langurs, who must now cross roads and navigate human-altered landscapes. Many fall victim to road accidents, predators, and even electrocution from overhead power lines. Moreover, being forced into new, unfamiliar areas has led to higher physiological stress, altered diets, and increased parasitic infections.

One of the most alarming consequences of this fragmentation is the rise in road accidents involving golden langurs. Dr. Biswas and his team have been meticulously documenting road kills and other hazards since 2013 in the Nadangiri, Nayekgaon, and Chakrashilla Wildlife Sanctuary areas. Along State Highway 14 (SH-14), the team observed a disturbing trend: on 71% of occasions, golden langurs would cross the road at ground level, oblivious to the danger of oncoming traffic. The remaining 29% of the time, they used the remaining canopy connectivity, altering their route to avoid vehicles. Yet, the result is clear—roads have become death traps. Between June 2022 and February 2024, 17 road collisions were documented along the stretch from Nayekgaon to Charaibari on SH-14, resulting in six fatalities and numerous injuries.

To address the rising threat of road fatalities and restore the fragmented habitats of golden langurs, conservationists have turned to innovative measures, such as artificial canopy bridges (ACBs). These bridges provide a safe passage for the langurs by reconnecting fragmented patches of forests. The first of these ACBs was installed in the Nayekgaon-Rubber Garden-Baxamara-Amguri forest complex in Kokrajhar district, where road collisions were most prevalent.

The construction of these bridges was no small feat. Dr. Biswas’ team meticulously collected data on the length, height, and viability of potential bridge sites. They experimented with various materials, ultimately choosing HDPE (high-density polyethylene) pipes and plastic ropes, which offered durability, environmental resistance, and visibility. HDPE pipes, known for their low thermal conductivity and resilience, proved ideal for this task. The pipes were lightweight, allowing easy installation on the anchor trees, and their black color blended naturally into the environment.

The first ACB installations, a combination of bamboo, mixed bamboo-cum-rope, and HDPE pipes, were secured by ropes tied to anchor trees along SH-14. These bridges were monitored using camera traps, which revealed encouraging results: golden langurs showed a preference for using the pipe bridges, which had a more appealing appearance and safer structure. Though it took several months, particularly during the monsoon season, golden langurs gradually began to use these bridges, and by early 2024, regular crossings were observed.

In addition to ACBs, the team designed ladder bridges at their field station in Siljan, Kokrajhar. Using materials such as PVC pipes, steel cables, and tie ropes, the team created four such bridges to aid langur crossings during the dry seasons. However, it took six months for the primates to adapt to these structures. Dr. Biswas noted that, while the langurs were initially hesitant, the bridges became an essential part of their movement patterns by January 2024. As the dry season intensified, langur groups were observed frequently using these ladder bridges to safely cross previously dangerous roads.

Beyond physical infrastructure, a critical component of the conservation strategy involves engaging local communities. Conservationists are working to educate and involve villagers in planting trees in their backyards, a grassroots effort aimed at restoring natural corridors for golden langurs. By connecting forest fragments through reforestation, these initiatives create the possibility for future population exchange among isolated langur groups. The communities in Nadangiri, Baxamara, Amguri, Nayekgaon, and Chakrashilla are vital partners in this effort, as their participation can help reverse the trend of habitat fragmentation.

As golden langurs continue to navigate the challenges of a shrinking and fragmented habitat, the future of this endangered species lies in the hands of conservationists, local communities, and innovative solutions like artificial canopy bridges. The efforts to restore landscape connectivity, mitigate road accidents, and engage local populations offer a beacon of hope for the survival of one of India’s most iconic primates. Yet, the fight is far from over. The task of securing the golden langur’s future will require continued dedication, innovation, and collaboration across all levels of society.