Road Death Toll: 7,000 Frogs Per Mile

Photo: Andrew DeWoody / Purdue University

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In just one 11-mile stretch of road killed 9,300 frogs in a 17-month period, according to a new Purdue University study published in Herpetological Conservation and Biology. That's 845 frogs per mile.

But 75% of the kills occurred along a single one-mile stretch, meaning the death toll on that one mile of road is closer to 7,000. Even that number is an under-estimate, given that many dead decomposed or were scavenged before being counted.

The results aren't surprising in one respect: The high-kill area is near a wildlife-rich wetland in Lafayette, Ind. called Celery Bog. Frogs, salamanders and turtles are among the species that live part of their live in water and part on land, meaning they can be found at different times of the year traversing land adjacent to, or between, wetlands. Many turtles lay eggs on dry land, for instance, and many tree frogs breed in vernal pools that fill only during the spring.There are two overriding lessons from this research. One, roads should be built thoughtfully, and not through or adjacent to wetlands where frogs, salamanders, turtles and other wildlife live. (Those roads that can't be avoided in these habitats should be built with underpasses to accommodate seasonal migrations, if the wildlife isn't to be decimated.) Two, avoid driving on warm rainy nights, starting in early spring and stretching through the summer. This is when wetlands wildlife is most likely to be on the move, and in the path of cars.

In other words, it's when frogs, salamanders and turtles are most likely to become roadkill.

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