Why didn’t the turtles cross the road?

By Rayla Bellis

A study from Ohio University evaluating the impacts of a new bypass on Eastern Box Turtles found unexpected results: turtles living next to the bypass did not exhibit heightened stress levels, but not one of them crossed the road over a two year period, including via a culvert.

The research team studied turtles near the relatively new Nelsonville Bypass (U.S. 33), which cuts through Wayne National Forest and first opened to traffic in 2013. The team tracked 30 box turtles for two years (2017-2018)—fifteen living along the bypass and 15 in a nearby control site with no road on Hocking College and Wayne National Forest lands.

Credit: Conserve Wildlife Foundation of NJ. Photo by Ben Wurst

While the team guessed that turtles living near the bypass would exhibit higher stress due to noise, light, and vibration (evaluated by measuring concentrations of the stress hormone keratin corticosterone in nail clippings before and after the study period), turtles at both sites showed the same levels of stress. The seemingly unfazed study subjects also used the same types of habitats at both sites, suggesting that box turtles have the capacity to adapt to new conditions rapidly.

However, none of the bypass turtles attempted to cross the road during the study period, an unexpected finding given that box turtles are commonly spotted intrepidly crossing roads in this part of Ohio. The box turtles also had the option to cross U.S. 33 via a four-foot-wide culvert underneath the highway, but none of the turtles accessed the mitigation structure. This restricted movement has potentially serious implications. As Ohio University’s Dr. Viorel Popescu notes, “cutting gene flow may have long-term negative impacts on the viability of turtle populations and decrease their ability to cope with other threats.”

These results suggest that there is still a lot we don’t know about the effects of transportation infrastructure on wildlife and how best to mitigate them: why might a road become a total barrier to migration for certain animals (temporarily or permanently), what are the long-term impacts, and how can we provide safe crossings that wildlife will actually use?

Rayla Bellis is a Program Manager at SSTI.