Crossing the Road Safely: How Tunnels and Fences can Reduce Herpetofauna Mortality


Yashi Dwivedi

A country’s social and economic progress is aided by rapidly expanding road networks, but animals often pay a heavy price for such development. Roads passing through natural habitats hinder animal movement and increase the risk of animals being hit by vehicles while trying to cross.

While road accidents involving larger species like the tiger and elephant often get reported, there is little information available on the impact of roads on smaller animals like birds, reptiles, and amphibians that are equally rare, endangered, or threatened. These species are vulnerable to road effects because of their smaller size, relatively slower speed, and limited road avoidance behaviour, as the asphalt provides warmth on cooler evenings. This is of concern as reptiles and amphibians are among the most rapidly declining taxa globally.

Given their vulnerability, ensuring presence of proper mitigation measures is critical. Mitigation measures are often a combination of barriers (such as fences) that prevent species from crossing roads and lower the risk of mortality, and crossing structures (such as tunnels and underpasses) that provide safe passage for smaller wildlife; facilitating movement and improving wildlife connectivity. However, just incorporating such mitigation methods does not always ensure alleviation of the negative impacts of roads. In order to ensure and improve the success of mitigation measures, examining their use and effectiveness by the target species is vital.

In a recent study, scientists from Laurentian University in Ontario, Canada, investigated the impact of mitigation measures on amphibian and reptile populations in Presqu’ile Provincial Park (PPP), Ontario, Canada. PPP is home to five species of turtles and snakes, three species of salamanders, and nine species of frogs. A road runs right through this park. Although the park did not have any mitigation measures in place when established, a combination of fencing (to prevent crossings), and a couple of tunnels to facilitate crossing were put in place a few years ago. The authors wanted to understand whether mitigation promotes connectivity while lowering mortality. For that, they gathered data on roadkill and successful road crossings before, during, and after the mitigation structures were built. Data was collected using camera-traps placed on either side of the tunnels to capture the species using them. Along with cameras, the authors also tagged a subset of the species using PIT tags and installed scanners to detect the tags at one end of the tunnels.  Additionally, surveys were done three times a day on bicycles to detect road kills and crossings along the road between  2013 and 2018. Surveyors walked the road after conducting bicycle surveys so as to maximise detections.

A Midland Painted Turtle in Presqu’ile Provincial Park (Image Credit: K. Osborne)

The authors found that mitigation measures significantly reduced the number of turtles and amphibians on the road. However, they did not have an impact on the number of snakes found on the roads, likely because the snakes were thin enough to  traverse through the fence. Tunnel usage by all studied species was high. Cameras recorded 72 snakes, 615 frogs, 217 salamanders, and 54 turtles using tunnels. In order to understand if the number of crossings observed was enough to maintain connectivity and prevent negative impact of the road on species populations, the authors estimated the population size of a couple of study species—the painted and snapping turtles—in the study area. They found that 5% of painted turtles and 12% of snapping turtles used the tunnels for crossing the road during the study period. Based on other studies, authors suggest this is likely to be enough to prevent road impacts. However, they acknowledge that further investigation is needed.

Mitigation measures that ensure roads do not fragment wildlife habitats are gaining global popularity and are increasingly being incorporated into infrastructure projects within India. However, most of the current mitigation measures are focused on large mammals. Structures like box and pipe culverts, routinely built for passage of water and small streams under roads or railways are often used by amphibians and reptiles. Incorporating considerations around ecology and biology of smaller species while planning placement and design of these culverts, could be a first step towards conservation of often-ignored species. Amphibians and reptiles are essential to the health of the environment and are valuable for natural biological pest control since they are significant predators of numerous insects and agricultural pests. It is important we don’t ignore the little stuff when it comes to linear infrastructure and road-impact mitigation.

Thumbnail Image Credit: A Snapping Turtle in Ontario, Toronto Star