A bridge for the tiger: the story of mitigation measures on India’s oldest highway

Being a developing country, India is at the forefront of road development to fulfil the developmental aspirations its people. India is also one the world’s most biodiverse countries and home to 70% of the world’s wild tiger population residing within and outside its network of protected areas. Corridors that enable tiger movement between these habitats are currently under threat from road development, by causing mortality of dispersing individuals and creating barriers to movement and genetic exchange among populations. However with recognition of the impacts of roads on long-term survival of tigers and associated species, mitigation measures are increasingly being implemented with road development projects in India.
National Highway 44 is a vital north-south highway and intersects several important tiger corridors. It passes through the Pench Tiger Reserve, an important tiger source for Central Indian tiger population, connected via corridors to neighbouring tiger populations. Nine wildlife crossing structures (CS), ranging between 50-750 m in width, were constructed when NH 44 was being up-graded from 2-lane to 4-lane configuration.
We report the results of the first long-term CS monitoring project in India (3 years and ongoing). We used camera traps to assess spatio-temporal use of the CS and adjacent habitat by wildlife (before and after construction of CS). Between 2019 and 2021, 21 species of wild mammals were using the CS with varying frequencies. Highest species richness was recorded under the largest CS. Tigers, wild dogs, most small mammals and ungulates used CS near Pench more, while ungulates and small mammals preferred CS with proximal vegetation cover. Similar capture rates for large carnivores between CS and adjacent habitat were observed. We found varied responses by structure generalists and specialists, a consequence of animal behaviour and tolerance to human disturbance. Construction of CS increased habitat use near roads of some large mammals as compared to that before construction. Temporal activity at different sites (underpasses, adjacent and control habitat) varied among wildlife species, possibly because of factors such as avoidance of traffic-related and anthropogenic disturbance, conspecifics and predators.
Currently, a large body of literature exists pertaining to CS design and use in the West. However such information from tiger landscapes and the Indian subcontinent is lacking. Through long-term monitoring of these CS, we aim to fill this lacuna and to increase the acceptability of CS as important strategies for mitigating the impact of linear infrastructure on wildlife in tiger landscapes. Our study is important since the measures are among the first dedicated wildlife mitigation measures on highways in the country and have the potential to inform future measures in tiger range countries.