April 17, 2008 -- All Dirty Jobs jokes aside: A surprising new study on road kill suggests some species, particularly amphibians, are so often victims of motorists that the phenomenon may help explain the decline of entire populations.
Even the researchers who worked on the study had close calls while counting and identifying mangled animal bodies alongside roads in Indiana, where the research was conducted.
To find their study subjects, the researchers drove slowly in vehicles marked with light beacons, said coauthor David Glista. They worked in two-person teams "so there were extra eyes to observe traffic," he said, adding that there were frightening instances "where we had to question some motorists' skills."
"I didn't want to become one of my own data points," added Glista's colleague, Andrew DeWoody.
The scientists focused their survey on four Indiana roads covering 11 miles, through urban and rural areas. Glista, then a Purdue University researcher who is now a scientist with the Indiana Department of Transportation, and colleagues DeWoody and Travis DeVault counted road kill on the routes twice weekly for over a year. They used a GPS unit to mark locations, also noting the weather and surrounding habitats.
Back at Purdue, they compiled the information into a database and were shocked by the results.
During the survey, they found 10,500 dead animals representing 69 species. Ninety-five percent were amphibians and reptiles, with bullfrogs and other frogs, often too damaged to fully identify, topping the list. The most frequently listed birds and mammals were opossums (79) and chimney swifts (36). The bodies of shrews, skunks, voles, muskrats, mice, raccoons, squirrels, Eastern cottontails, song sparrows, European starlings, American robins, turtles and snakes were also documented.
The findings are published in the journal Herpetological Conservation and Biology.
"We could only count what we saw during our surveys, but we do feel that what we found may be an underestimate because of scavenging, degradation or moving of carcasses in between surveys," Glista said. "It could be anywhere between two and 10 times as many."
The majority of animal-car collisions occurred from July through September during periods of peak temperature and rainfall. The researchers suspect most birds were flying too low while chasing insects. The amphibians and mammals, however, appear to have either been drawn by water sources near the roads or attempting to cross areas where the roads cut through habitats.
"I think most of the problem is habitat-driven -- no pun intended -- especially when roads bisect prime habitat," Glista said, adding that amphibian deaths were greatest on a road that cut a wetland in half.
The frog carnage was so overwhelming that the researchers suspect road kill could help explain why amphibian populations have plummeted in recent years. They add that habitat degradation, climate change, infectious disease and UV radiation also appear to be major factors contributing to amphibian and reptile declines worldwide.
Kenneth Dodd, a scientist in the University of Florida's Department of Wildlife Ecology and Conservation, told Discovery News that "we very much need this type of documentation concerning the effects of roads on wildlife," especially reptiles and amphibians.
"Roads take a tremendous toll on amphibian and reptile populations, a mortality that is often overlooked because their bodies are delicate and quickly obliterated or scavenged," he explained. "Amphibians and reptiles living near roads tend to disappear slowly, and you suddenly realize they are not there anymore."
"What we need are ways to mitigate this mortality, especially at road crossing 'hot spots,'" Dodd added. "The type of work that David and his team conducted will help us identify these hot spots, so that eco-passages can be provided. Europe is far advanced of North America in that regard, but this work will help raise awareness so that these measures can be employed here."
Related Links:
Jennifer Viegas' blog: Born Animal
Frogs: A Chorus of Colors (American Museum of Natural History