Turtles Decline Due to Road Kill

Aug. 9, 2001 -- 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."

Other estimates have shown that road kill mortality rates in general are high. A current, ongoing survey by a secondary school teacher in New Hampshire, Brewster Bartlett (a.k.a. Dr. Splatt) and his network of students places daily road kill mortality at about a half million animals a day. The Animal Protection Institute in Sacramento, Calif., suspects this estimate is low and may actually be as high as 1 million a day since struck animals often crawl away from roads before dying.

Some have been seeking ways to stop the carnage. Madeleine Linck, a wildlife technician with the Suburban Hennepin Regional Park District in Minnesota, launches a statewide publicity campaign on radio and newspapers every spring for motorists to be wary of crossing turtles. Minnesota's endangered Blandings turtle is known to venture out onto roads at this time of year to find places to lay their eggs.

"Just ride around the block around here in June and you'll see dead carcasses everywhere," she says. "Anyone who walks along a major road sees tons of shell fragments."

Jeffrey Lang, a biologist at the University of North Dakota in Grand Forks is researching what size culverts turtles and tortoises are likely to pass through rather than lumbering across treacherous paved highways. His work so far suggests 3-to-4-foot wide underground passageways might appeal to most of the shell-covered reptiles.

Pet Collectors Also Threat

Apart from increasing road kills, Gibbs suspects one other factor might be behind the population declines — pet collectors. He points out that spotted turtles can be sold for hundreds of dollars in Europe and that may be having a big impact on the animal.

"When a turtle is picked up by a person, it has the same effect as road kill — the animal and its future offspring are lost," he says.

Pet turtles, he says, usually don't reproduce and often die in captivity.

Most turtles put off sexual reproduction for up to 12 years and instead expend their energy growing their protective shells. In evolutionary terms, that's a big sacrifice. But their hard-earned shells offer long-term rewards. Under normal conditions, the reptiles can live for 60, sometimes even 70 years. Gibbs fears that now there may be a big problem with that life plan.

"Shells have protected adult turtles for eons," he says. "But suddenly there's a new element in the environment and evolution can't catch up fast enough."