Several international donor and lending agencies are providing economic impetus for the expansion of the road network that includes highways as well as rural roads. However, this road development could negatively impact critical tiger habitats through increased fragmentation, road mortality due to speeding vehicles (both tiger and its prey), modification of wildlife behaviour and restricting the movement of animals by acting as physical barriers. Since highways fragment and isolate wildlife populations they could directly and negatively impact the genetic diversity of a population. This is especially true for wide-ranging and large carnivores such as tigers. Nagarahole and Bandipur Tiger Reserves in India have some of the highest tiger and prey densities anywhere in the world.
To mitigate this potential conflict, the Nagarahole Road Construction Agency planned to incorporate rumble strips and humps, and to upgrade existing culverts to act as wildlife underpasses. However, these measures were not properly researched and WCS maintain that they could be ineffective.
In this study, WCS-India carried out camera trapping to assess movements of wildlife near the road. Vehicle usage was monitored and structural measurements of all culverts and bridges taken and their condition recorded.
Analysis of animal tracks on specially placed sand track plots and faecal matter of wildlife gave information on the usage of existing water culverts as underpasses by wildlife.
WCS monitored three different sectors of the highway:
- That had no day or night time vehicular traffic
- A sector that had only day time traffic
- A sector of the highway that had day time traffic and human habitations.
The final report shows that vehicular density on the Mysore-Mananthavadi Highway has increased by 1100 per cent since 2003. Vehicular speed is one of the important determinants of road kills, hence implementing speed calming measures is an important measure for reducing road-kills. Traffic density and human habitations seem to result in avoidance of these areas by wildlife especially tigers, elephants, gaur and other species that are sensitive to disturbance. More crossing takes place in quieter times.
Camera trap results clearly indicate that the existing culverts do not function as underpasses for wildlife. These culverts were built solely for hydrology purposes and do not to facilitate wildlife crossings. Environmental Impact Assessments about highway construction need to consider this aspect.
Within a 12.2 km road stretch WCS photo captured four different individual tigers indicating high usage of this area by these felids. This highlights the importance of this corridor for tiger conservation hence making a stronger case to control and reduce the impacts of this highway on wildlife and its habitat.
This study highlights the point that impact assessment on wildlife by projects like these needs scientific and quantitative assessments carried out by trained wildlife biologists and not through rapid Environment Impact Assessments. A framework for addressing their effects through conservation planning that would address the immediate impacts as well as provide long-term solutions for reducing impact of linear intrusions like highways on wildlife needs to be developed. This is specifically required with respect to endangered wildlife species like tiger. The location of speed calming measures and culverts have to be suggested by wildlife biologists who have a comprehensive understanding of the site and behaviour of wildlife.
Although roads are important for economic development, poor planning, disregard of ecological aspects and excessive road expansion into wildlife habitats will further fragment and destroy wildlife populations and their habitats in the long-term.
Based on this WCS work, the Government is working on a plan to divert a part of this highway to outside the national park limits, thereby minimising the impact of the highway on this important corridor.
This critical study will establish base-line facts for distribution to the Forest Department as well as the project engineers and will be hugely useful in the future whenever a road is planned through important wildlife habitat.