Two Wildlife Tunnels Are Saving Thousands of Amphibians From Being Crushed by Cars in Vermont
New research finds a pair of underpasses installed under a road that crosses a migration corridor have led to an 80.2 percent reduction in amphibian deaths
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Every spring, salamanders, frogs and other amphibians in the northeastern United States migrate to their breeding grounds. Though some only need to travel a few hundred feet, their journeys often take them across busy roadways, and many end up being crushed by vehicles.
But ecologists say this problem has a simple yet highly effective solution: wildlife underpasses. In Vermont, two underpasses installed nearly a decade ago have dramatically reduced amphibian deaths, cutting the animals’ mortality by more than 80 percent, according to a new paper published in the Journal for Nature Conservation.
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In the Northeast, amphibians spend the winter hiding out below ground, as well as under rocks and logs. In late March and April, they emerge and begin to make their way from upland forests to ponds, wetlands and flooded meadows to reproduce. They move at night, typically on warm, rainy evenings.
Unfortunately, this trek often requires them to cross roads. Though large mammals can sprint across a road in just a few seconds, amphibians move much more slowly. They may spend several minutes in the street—ample time to get hit by a car. Because hundreds or thousands of amphibians are migrating at the same time, this arrangement causes high numbers of amphibian deaths each spring.
Around Monkton, Vermont, the migration includes creatures like spotted salamanders, eastern newts, four-toed salamanders, wood frogs, spring peepers, northern leopard frogs and American toads, among others.
In 2015, officials installed two concrete tunnels under a roughly 0.8-mile stretch of road that crosses the amphibians’ migration path. One was about five feet tall, while the other was approximately three feet tall; both were four to five feet wide. Crews also built metal grates into the road above the tunnels so that moisture could pass through and amphibians could still see the moonlight, which helps guide them on their journey, reports Forbes’ Noël Fletcher.
Thanks to wildlife cameras, conservationists knew amphibians were using the tunnels. But to get a sense of their overall effectiveness, they wanted to see some before and after data.
For the study, scientists compared amphibian road mortality in the five years before the tunnels were installed (2011 to 2015) with the seven years after (2016 to 2022). They looked at the areas with the underpasses, the “buffer” zones right beside them and “control” sites far from the new construction.
The results were staggering: The underpasses contributed to an 80.2 percent reduction in deaths among all amphibians. When the researchers removed climbing species, like spring peeper frogs, from the numbers and looked only at ground-dwelling species like salamanders and toads, they saw a 94 percent decrease in deaths.
“I knew that underpasses would work, but I didn’t think they would be that effective,” says lead author Matthew Marcelino, an ecologist at the University of Vermont, in a statement. The team’s monitoring efforts at the buffer zones suggest the animals were using the underpasses—not just relocating to the areas beside them.
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The results also affirm some of the design decisions conservationists made while building the Monkton underpasses. When they installed the concrete tunnels, they also added “wing walls” extending from the sides, which they hoped would guide the amphibians toward the underpasses and away from the road. If an amphibian traveled the wrong way along the wing wall, it would reach a “U-shaped turnaround” and be pointed back toward the tunnel, as Jens Hawkins-Hilke, a conservation planner with the Vermont Fish & Wildlife Department, tells Ike Bendavid of WCAX.
The data suggest the wing walls are effective. However, the researchers indicate their design could be improved to help reduce amphibian deaths even more. For instance, future studies might investigate the effectiveness of “turnarounds” and other modifications that could prevent climbing amphibians from scaling the wing walls and ending up on the roadway, they write in the paper.
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Overall, the success of the Monkton underpass project highlights the important role of community members in conservation work. The initiative dates back to spring 2006, when residents counted more than 1,000 dead amphibians on the road over the course of two nights.
Shocked and disheartened, they rallied to try to protect the creatures moving forward. Residents began collaborating with state agencies, scientists and conservation groups like the Monkton Conservation Commission, the Lewis Creek Association and the Vermont Reptile and Amphibian Atlas.
Eventually, they were able to win the support of the Vermont Fish and Wildlife Department and the Town of Monkton, which gave the go-ahead for the underpasses. These conservation groups, along with state and local agencies, worked to crowdsource donations and earn grants to fund the project. Together, the tunnels cost $342,397 to build, which experts note is much cheaper than underpasses and overpasses for large mammals.
While the new study focused only on amphibians, wildlife cameras have also captured many other creatures using the underpasses. Bears, bobcats, porcupines, raccoons, snakes and even birds use them to traverse the busy road, which suggests the citizen-led project was a boon to the entire ecosystem.
Scientists hope the Monkton project will serve as a model for other communities.
“The power of Monkton is in the story and exciting people in Vermont and around the Northeast, and hopefully even around the world, that we can have a transportation system that works effectively for the traveling public and also stewards our wildlife,” says Hawkins-Hilke to Forbes. “It’s not an either-or. We can have both.”
