Turtles Decline Due to Road Kill

Aug. 9 -- The slow-moving turtle is ending up as road kill.

For millions of years, the reptiles have been nearly invincible by growing hard shells that protect them wherever they go. When a predator approaches they can quickly retreat under their cover, safe from harm. Only a select few predators like the coyote and wolf are known to be able to crack through an adult turtle's armor.

Then came the automobile.

About one-third of U.S. turtle species are reaching dangerously low numbers — and in nearly every state of the nation at least one species of turtle is listed as threatened or endangered. Scientists believe the declining numbers may be caused by increasing traffic near their homelands.

"For the fleet of foot, like deer or rabbits, traffic is not as much of an issue," says James Gibbs, a conservation biologist at State University of New York in Syracuse. "But these ground-hugging animals are much more vulnerable."

Calculating Turtle Kills

While no one has recently attempted to go out and count the total numbers of turtles that are crushed by cars throughout the United States every year, Gibbs decided to make an educated estimate. To do this he considered three main factors: the number of roads in the United States, traffic density and the speed (or lack thereof) with which turtles cross the two-tire-width kill zone of a road (about 5-10 seconds).

He found that turtle populations in the Northeast, Southeast and Great Lakes region suffer at least a 10 percent annual kill rate from road kills, and that some of these regions likely have up to 20 percent mortality rates due to traffic encounters. Those rates are high enough, says Gibbs, to seriously deplete turtle populations and could well account for the fact that wood turtles, Blandings turtles and box turtles have nearly vanished from many regions in recent years.

"Grandparents talk about finding box turtles in their backyards two generations ago," says Gibbs. "Now most would be very hard pressed to find any of these animals around."