"Toad Tunnels" Built to Help Amphibians Cross Roads

John Roach
for National Geographic News
April 15, 2005
Later this month, when the next warm, wet rain soaks the northeastern
U.S., it will signal thousands of American toads to hop to their
breeding ponds. To get there, many of the toads will cross roads that
slice through their habitat.

John Serrao, a naturalist in Pennsylvania's Pocono Mountains, says that unless Buffo americanus and other amphibians get help crossing the road, their local populations will disappear.

Entire populations of American toads breed within the same few days at the same time each year, usually late April or early May.

According to Serrao, the toads hop to their breeding ponds after the ground has warmed, the air temperature stays above 65° Fahrenheit (18° Celsius), and the first hard spring rain falls.

"To get to their ancestral breeding ponds, a lot [of toads] have to cross roads," Serrao said. "And they're slow moving at that time of year—it's still cool, they've been inactive—and they get squashed."

Serrao recalls an April night five years ago when he went out to a backcountry road near his home to watch the breeding migration. He counted 100 toads; 95 were hit by cars.

A similar story can be told for several other species of toads, frogs, salamanders, alligators, and turtles around the world.

Roadkill is just one factor behind the dramatic decline of the world's amphibians. By one count, 1 in 3 of the 5,743 known species of frog, toad, salamander, and other amphibians are dwindling.

Better-known suspected culprits for the decline include global warming, insecticides, and paved-over wetlands.

Amphibian Tunnels

Scott Jackson, a biologist at the University of Massachusetts in Amherst, said one way to help amphibians survive road crossings is to construct so-called amphibian tunnels beneath the pavement.

European countries have constructed these amphibian tunnels for decades. Jackson led a team that installed the first such tunnel in the U.S., which was built in Amherst in 1987.

The tunnel, known as the Henry Street site, was constructed to help spotted salamanders (Ambystoma maculatum). More than three quarters of the local salamander population used it to cross the road, according to monitoring results.

Based on his experience with the Henry Street site and knowledge of other amphibian tunnels in Europe, Jackson has prepared and posted to a Web site his recommendations for appropriate tunnel design.

He says tunnels should be a two-foot-by-two-foot (0.6-meter-by-0.6-meter) box, open at the top, and fitted with an iron grate to allow sufficient air, light, and moisture into the tunnel.

In addition, barricades, such as fences or walls, should extend out from either side of a tunnel for about 100 feet (30 meters). This serves to guide amphibians toward the tunnels.

Jackson estimates that there are about a hundred amphibian tunnels in the U.S. today. But he said he is not sure how effective they are at protecting amphibians.

"There have been a lot built but not necessarily with careful design and careful planning, and no one knows how well they are working," he said.

The biologist said developers of housing subdivisions and industrial parks often approach him for amphibian-tunnel advice but then downgrade the designs in order to save money.

For example, Jackson said that many developers will not use iron grates or slots to allow moisture into amphibian tunnels, which the animals need to keep moving.

"So, very often it's considered a success just to get these installed. I haven't heard much back whether or not they are working," he said.

Road Closure

Biologists know the time of year and the conditions that cue to amphibians to breed. This means temporary road closures would be an effective way to prevent roadkill, according to Serrao, the Pennsylvania naturalist.

Serrao was instrumental in one such temporary road closure at the Delaware Water Gap National Recreation Area in the Pocono Mountains. It was there in March 2002 that he saw more than 700 amphibians squashed on just a 200-yard (183-meter) stretch of road.

"I talked to the park superintendent, and from now on they close off that road on the [first] four or five … rainy nights of the spring, when the amphibians come out," he said.

According to the National Park Service, a biologist who monitored the road during the first closure in March 2003 counted nearly 500 amphibians successfully crossing the road.

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