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Traffic May Curb Turtle Numbers

1 August 2001 7:00 pm
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Look out! In much of the U.S., traffic probably diminishes turtle populations.

HILO, HAWAII--Jaywalking may be the reason why many species of land turtles in the United States are dwindling, according to research presented here 31 July at the Society for Conservation Biology meeting. In much of the Eastern United States, the density of roads and volume of traffic are high enough to cause at least 10% annual mortality among adult turtles--a kill rate high enough to send populations into decline.

About one-third of U.S. turtle species are in trouble, and some of the most threatened are land turtles. Such turtles, including box turtles, wood turtles, spotted turtles and tortoises, plod between wetlands and drier regions during the year. Although most days turtles just lumber around, moving only 50 meters or so, about once a month they trek 500 meters or more. In many areas this means that the turtle crosses a road.

Rather than just tally up totaled turtles, James Gibbs and Gregory Shriver, conservation biologists at the State University of New York in Syracuse, decided to figure out under what circumstances turtle populations would suffer at least 10% annual mortality from roads--a kill rate likely to cause population declines. By combining information on turtle movements, including the speed with which turtles crossed the two-tire-width death zone (5 seconds), with Federal Highway Administration information such as road density, traffic volume, and miles driven per year per vehicle, the team figured out that for much of the Western U.S., road mortality for turtles is probably less than 10%. But in the Eastern states, many of which are home to more than three species of land turtles each, mortality rates would exceed 10%.

Gibbs says this study may help explain "why the wood turtles and other similar land turtles have vanished," adding, "Some of these animals have disappeared too quickly, way out of pace with habitat loss." Gordon Rodda, a zoologist with the U.S. Geological Survey in Fort Collins, Colorado, says the study is "an important wake-up call for the overall problem--a decline of a whole suite of different species over a broad area of the U.S."

Related sites

Turtle photos and links
The tortoise trust

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