Saving amphibians: Wildlife tunnels prevent road deaths

Frogs, salamanders, and other amphibians have long faced growing threats. Habitat loss, climate change, and deadly fungal infections are well-known dangers.

But there’s another, less visible threat: roads. Every year, millions of amphibians are killed as they attempt to cross busy roads, especially during their short migration season.

A new study brings fresh hope. Scientists, working alongside community members, found that simple wildlife underpass tunnels can sharply cut amphibian deaths. Their research, spanning more than a decade, focused on a small but important migration corridor in Monkton, Vermont.

A team from the University of Vermont collaborated with the Vermont Agency of Natural Resources and the local community. The research revealed striking results: an 80.2% reduction in amphibian deaths after underpass tunnels were installed.

“It was surprising. I knew that underpasses would work, but I didn’t think they would be that effective,” said Matthew Marcelino, an ecologist at UVM. “And when we took climbing amphibians out of the picture – which in our context are primarily spring peeper frogs – we noticed a 94% decrease in mortality in the treatment areas.”

Helping amphibians cross safely

To measure the tunnels’ effectiveness, the team used a “before-after-control-impact” (BACI) study design. This approach compared amphibian deaths before and after the underpass installation.

The analysis also accounted for different sections of the road: one with the tunnels (treatment), one just beyond the tunnels (buffer), and a control area far from the tunnels.

Over five years before construction (2011-2015) and seven years after (2016-2022), citizen scientists and researchers carefully monitored the spring migration. On rainy evenings, they walked the road, recording every amphibian, whether alive or dead. The team tracked twelve species, including frogs, toads, and salamanders.

Wildlife tunnels and death rates

The numbers were sobering. Of 5,273 amphibians observed, nearly half of the 1,702 spotted salamanders were dead. Almost 70% of the 2,545 spring peeper frogs didn’t make it across. But where underpasses were installed, death rates dropped dramatically.

Even in the buffer areas beyond the tunnels, deaths fell, showing that amphibians were using the tunnels rather than being pushed to new danger zones.

This work marks the first long-term, peer-reviewed study showing how effective amphibian-specific underpasses can be in the northeastern U.S. The results also highlight that design details like wall height, angles, and tunnel materials are key to success.

Breeding season for amphibians

Amphibians aren’t just cute – they are critical to healthy ecosystems. They control insect populations, serve as food for many predators, and signal environmental changes due to their sensitivity to pollution and habitat disruption.

In places like Vermont, many amphibians spend most of the year in upland forests or streams. They fatten up and survive the winter underground.

But in the early spring, something amazing happens. Warm, rainy nights trigger a mass migration. Frogs and salamanders emerge all at once, heading for ponds and wetlands to breed.

“It’s usually sometime between late March and late April,” explained Brittany Mosher, a professor at UVM. “Many species will breed in the same ponds. So it’s not just a single species migrating – it’s many, many species. And oftentimes, we see hundreds or thousands making this movement all at the same time.”

Roads are dangerous for amphibians

Professor Mosher noted that roads are often built between the steeper forested upland habitats and nice flat aquatic habitats. “So the roads are placed exactly in the wrong spot if you were an amphibian planner.”

Unlike deer or foxes that can quickly dart across, frogs and salamanders are slow. A single crossing can take several minutes. With hundreds migrating together, the risk of mass casualties is high.

In Monkton, the problem became too big to ignore. In 2006, local volunteers from the Monkton Conservation Commission and the Lewis Creek Association counted more than a thousand dead amphibians on the road in just two nights.

How a community took action

The shocking number of amphibian deaths caused the Monkton community to take action. Working with conservation groups, scientists, and state agencies, the town launched a project to save their local amphibians.

Led by long-time resident and wildlife biologist Steve Parren, the effort culminated in the construction of two wildlife underpasses in 2015.

The project cost $342,397, much less than large wildlife crossings for bigger animals, which can cost up to $100 million. The Vermont underpasses are two 4-foot-wide concrete tunnels with wing walls that guide amphibians safely under the road.

Wildlife cameras installed by the Lewis Creek Association captured more than 2,200 amphibians using one tunnel in the first spring alone. Other animals, including bears, bobcats, porcupines, raccoons, snakes, and birds, also used the tunnels. This suggests the underpasses have broad benefits for ecosystem connectivity.

For climbing amphibians like spring peepers, the reduction in deaths wasn’t statistically significant, though there was a 73% decrease. The greatest benefits were for non-arboreal species that walk along the ground. They used the tunnels consistently, and fatalities plunged.

A model for the future

The researchers hope their findings will encourage road planners to adopt similar underpasses in other regions.

“This study provides strong evidence that wildlife underpasses work,” Marcelino said. “We hope this will encourage transportation departments to include them in future plans, when building or repairing roads.”

Professor Mosher emphasized that these projects show the power of community action. “This story began with local community members who were engaged and concerned,” she said. “And it provides a view for how other communities can protect their amphibian populations too.”

In a world where conservation often seems daunting, the study sends a clear message. Long-term commitment, thoughtful design, and community involvement can make a big difference.

“Conservation takes commitment,” Marcelino added. “But when we invest in good tools and take the time to do it right, the payoff for ecosystems and wildlife can be enormous. These are beautiful creatures – so beautiful, so ancient.”

The full study was published in the journal Journal for Nature Conservation.

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