WSB Study: Partial fencing doesn’t keep reptiles off road

By Julia John

A Blanding’s turtle crosses an unfenced road in southwestern Ontario, Canada. ©Chantel Markle

Fencing just one side of a road cutting through wildlife habitat may minimize costs, but a new study from Ontario demonstrates that for reptiles, total fencing on both sides was the only effective way to block the animals from a hazardous thoroughfare and reduce the number that get run over.

“It’s where we installed complete fencing that we had the great decline,” said Chantel Markle, co-author on the paper published in the June issue of the Wildlife Society Bulletin. “We didn’t find partial to be an effective strategy in keeping animals off the road.”

In a wetland in southwestern Ontario, Markle and other researchers evaluated turtle and snake mortality on a two-mile stretch of a busy causeway, which was fenced on either or both sides in 2008 in a community-led initiative to prevent wildlife collisions with vehicles.

The research focused on turtles, including the at-risk Blanding’s turtle (Emydoidea blandingii), spotted turtle (Clemmys guttata) and snapping turtle (Chelydra serpentina), because their late sexual maturity and low juvenile recruitment make their populations slow to grow and vulnerable to decline, Markle said. It also looked at snakes, such as the eastern ribbonsnake (Thamnophis sauritus) and eastern foxsnake (Pantherophis vulpinus), because in addition to habitat loss, they face threats from humans, she said. The scientists compared roadkill frequency spanning from five years before the fencing went up through five years after.

“If you are capable of fencing both sides, the money should go to full fencing,” said Markle, a doctoral student at McMaster University. “That’s where you’re going to see your declines if you want to actively keep species off the road.”

Cutting costs by erecting fencing on only one side defeats its purpose, she said, because animals can get onto the thoroughfare wherever there’s a break in the structure. In some cases, partial fencing increased the likelihood of animals getting struck by traffic, Markle said, because they entered from the unfenced side, reached the fence and had to retrace their steps to escape, putting themselves in traffic twice. Biologists actually observed more snapping turtles in sections of partial fencing than those with full fencing, she said. Her team found it was important to make repairs quickly and to tailor the fencing to varying environmental conditions. Curving fence ends into the habitat helped redirect species away from the road, she said, and strategically placed culverts helped them access fenced-off habitat.

Markle said she hoped her study will help guide other road mortality projects and “encourage other communities in making a difference even at a local scale.”

TWS members can log into the member portal to read this paper in the June issue of Wildlife Society Bulletin. Go to Publications and then Wildlife Society Bulletin.

Julia John is a science writer at The Wildlife Society. Contact her at jjohn@wildlife.org with any questions or comments about her article.

Read more of Julia's articles here.