Avoiding roads: reptiles take paths less travelled

Blog written by James Paterson, Julia Riley, and Christina Davy. Read the full paper here.

There are currently more than 21 million kilometers of roads across the world. As the human population grows, that number is set to double in the next 30 years. Vehicle strikes are responsible for a large amount of wildlife death when animals cross roads. But, do roads also have less obvious impacts on wildlife? If crossing a road is risky, it may limit access to preferred habitats. Many animals avoid roads, like birds, caribou, and many reptiles, but no study has previously looked at how avoiding roads may affect a reptile’s energy costs or examined if animals avoid roads across multiple study sites.

We tracked turtles and snakes using radio-telemetry. Photo: Julia Riley

We studied two endangered species that often live near roads. Blanding’s turtles (Emydoidea blandingii) are medium-sized turtles that live in wetlands around the Great Lakes in North America. Eastern massasaugas (Sistrurus catenatus) are small, semi-aquatic rattlesnakes that live in wetlands, prairies, and alvars. We hypothesized that roads may change the behaviour of these reptiles, and that avoiding roads may be energetically costly. We predicted reptiles would avoid roads and reptiles living near roads would spend more energy moving because they have to travel further to reach their preferred habitats. To test these predictions, we used individual tracking data on 286 turtles and 49 snakes from 18 sites in eastern North America.

We found that turtles and rattlesnakes avoided crossing roads, but they didn’t avoid habitat near roads. Many turtles and snakes in our study still crossed roads, but they did so at a lower rate than we expected based on simulated paths.

Eastern massasaugas (Sistrurus catenatus) avoided crossing roads but did not avoid habitat near roads. Photo: Julia Riley

Rattlesnakes near roads did not move more than rattlesnakes living in areas without roads. In contrast, turtles living near roads spent more energy moving than turtles that didn’t live near roads. But, is this difference relevant to fitness? The extra energy spent by turtles near roads was less than the energy required to produce one egg. To put that in perspective, Blanding’s turtles lay between 8 and 25 eggs each year. Although living near roads resulted in higher energy costs, this difference is unlikely to significantly reduce the reproductive output or survival of turtles.

Blanding’s turtles (Emydoidea blandingii; left) with roads in their home ranges moved farther per day and spent more energy moving than turtles without roads in their home ranges. Eastern massasaugas (Sistrurus catenatus; right) with roads in their home range did not move significantly farther per day than snakes without roads in their home range. Photos and Figure: James Paterson

Our results suggest that reptiles change their behaviour in response to roads, but mortality from vehicle strikes remains the biggest known impact of roads on these populations. Future research should continue to explore ways to reduce wildlife mortality on roads, such as exclusion fencing and conservation-focused road planning.

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