Road Losses Add Up

Image Gallery Dead frogs and other roadkill line Lindberg Road, which traverses a wetland known as Celery Bog (in West Lafayette, Ind.) in this 2005 photo. Research shows that frogs and other amphibians are particularly hard hit by road-related death; it may be a contributing factor to their worldwide decline, says Purdue researcher Andrew DeWoody. Purdue University photo/Andrew DeWoody

West Lafayette, Indiana – When frogs hit the road, many croak.

Researchers found more than 65 animal species killed along a short stretch of roads in a Midwestern county. Nearly 95 percent of the total dead were frogs and other amphibians, suggesting that road-related death, or roadkill, possibly contributes to their worldwide decline, a trend that has concerned and puzzled scientists for decades.

The Purdue University study found that habitat along roadsides heavily influences road-kill. More than 75 percent of the carcasses originated alongside a 1-mile stretch of road that traverses a wildlife-friendly wetland known as Celery Bog in West Lafayette, Indiana.

"On hot summer nights when it rains, there are literally thousands of frogs out there," says Andrew DeWoody, a Purdue researcher who led the study in Tippecanoe County, home to the university.

During the 17-month study, researchers found 10,500 dead animals along 11 miles of roads. Of those, 7,600 were frogs of unidentifiable species and another 1,700 were bullfrogs, says DeWoody, an associate professor of forestry and natural resources.

"In addition to indirect costs of habitat fragmentation, roads have direct costs in terms of animals' lives," he says.

Several steps can be taken to help reduce road-kill, says Dave Glista, study co-author and a Purdue master's graduate who began the study as part of his since-completed thesis measuring roads' environmental impact. For one, development planning should take into account an area's wildlife value. Second, structures to mitigate, limit and prevent roadkill should be explored whenever possible, he says. Options include underpasses, viaducts and overpasses to allow wildlife safe passage, and special fences to keep animals off roads.

"We need to avoid, minimize and mitigate," says Glista, now a scientist with the Indiana Department of Transportation. "As a biologist, I do think we should avoid building roads in wetlands and other wildlife-rich areas. Mitigation structures are worth the cost, as is any measure we can take to minimize our impact on the overall environment."

Scientists estimate that one-third of amphibian species are threatened, and hundreds of species have gone extinct in the past two decades alone. Roadkill adds to numerous factors already implicated in amphibian declines, DeWoody says. These include habitat loss and degradation, disease, pollution, competition from introduced exotic species, and threats posed by climate change.