University of Georgia

Why did the terrapin cross the road?

A diamondback terrapin near a road

The ticking of a diamondback terrapin’s biological clock can lead to her death—unless she runs into a barrier, according to new research by UGA scientists.

Nearly all terrapin fatalities are caused when adult females looking for a place to lay their eggs wander into traffic, but creating artificial barriers can significantly reduce these deaths. The study found that a barrier erected along part of the Jekyll Island Causeway could keep nearly 58 percent of diamondback terrapins off that section of the road.

“Thousands of terrapins are struck each year on high-traffic roads in New Jersey, Maryland, Georgia and elsewhere,” said Brian Crawford, a postdoctoral researcher in the Warnell School of Forestry and Natural Resources. “It’s a chronic threat to populations, but it’s also an issue for people. Anytime you have that much wildlife on roads, you have to consider the safety of motorists.”

Nesting females seek areas above high tide lines, and that’s where roads are, Crawford said. The summer nesting season—May through July—brings hundreds of terrapins onto causeways near Jekyll, St. Simons and Tybee islands in Georgia. These vacation months also bring peak traffic on coastal roads.

In a paper published in Herpetological Conservation and Biology, Crawford and his collaborators say “hybrid barriers” could be key to helping terrapin populations recover on Jekyll Island as well as in other areas where the slow-moving reptiles often have fatal encounters with vehicles.

The barriers serve the terrapins in two ways. Their short fencing prevents female terrapins from getting to the road. In addition, the structure offers boxes that provide attractive nesting habitat and protection from predators.

Researchers tested a section of the Jekyll Island Causeway, which connects the mainland with Jekyll Island and brings more than 3,400 cars every day, peaking during the summer tourist season. This 55 mph road is also the site of between 100 and 400 adult female terrapin deaths each summer.

Using data spanning several years, the researchers monitored the number of terrapins crossing at three causeway “hot spots” for fatalities. Halfway through the study, they constructed a barrier at one hot spot and were able to compare the number of deaths before and after, as well as how turtles fared at the two hot spots with no barriers.

The results were striking. The site with the hybrid barriers had a 57.3 percent reduction in the number of terrapins emerging onto the road. At the two unblocked sites, there was no change.

Diamondback terrapins are native to the coastal tidal marshes of the eastern and southern U.S. and are found as far north as Massachusetts, as far south as the tip of Florida, and as far west as Texas. They are listed as endangered species in some states.

In addition to being hit by vehicles, diamondback terrapin populations have been affected by habitat loss, commercial and recreational crabbing, and increased numbers of raccoons and other predators that raid terrapin nests. If road deaths and nest loss on Jekyll Island aren’t addressed, Crawford said, the terrapin population there could ultimately disappear.

“There are always many threats impacting wildlife simultaneously, and there’s a growing awareness that conservation strategies won’t be successful if they only focus on one thing,” he said. “This study was an example of designing one management device that had multiple benefits to wildlife populations. The barriers were effective, but there’s always more to do.”

This story appeared in the fall 2017 issue of Research Magazine. The original press release is available at