Mitigating linear infrastructure: Artificial canopy bridges as a key mitigating tool to reduce golden langur (Trachypithecus geei) road accidents in Assam, India

Abstract

Linear infrastructures like roads and power lines fragment the forest habitats used by golden langurs (Trachypithecus geei) in Assam, India. Artificial gaps in the forest canopy force these arboreal primates to descend to the ground, resulting in roadkill and other forms of anthropogenic mortality. From January 2023 to December 2024, a study in the Chakrashila–Amguri–Buxamara–Nayekgaon forest complex recorded 18 langur-vehicle collisions in the Nayekgaon-Choibari section of the State Highway- 14 (SH-14), leading to seven deaths, five major injuries, and six minor injuries. To mitigate these risks, 15 artificial canopy bridges of four designs were installed along SH-14. During the monitoring, 112 instances of road and canopy bridge crossings by eight golden langur groups were recorded. Langurs used canopy bridges (74%, n = 83) significantly more than the road (χ² = 26.04, df = 1, p < 0.01). Among canopy bridges, pipe (69.9%) and ladder bridges (26.5%) were most effective, reducing ground-level crossings and probable collisions by ~74% during the study. Some power lines in the study area were insulated, providing additional pathways for their movement across the road. The initiative also integrates community outreach education to promote the conservation of golden langurs, providing incentives for restoring corridors through plantations, and maintaining them to mitigate conflicts. These interventions can restore fragmented habitat and, thus, corridor connectivity, reduce mortality risk, and are expected to enhance their persistence in the fragmented landscape.