Wildlife underpass reduces squished amphibians by 80%

Innovative solutions are emerging to address the peril faced by migrating amphibians, with the implementation of simple yet effective structures-namely, wildlife underpass tunnels. A comprehensive study conducted over more than a decade in Vermont reveals that these crossings can reduce amphibian mortality rates by up to 80.2%, simultaneously contributing to ecosystem preservation. The detailed results are published in the August 2025 issue of the Journal of Nature Conservation.

“The results exceeded our expectations. I was confident that underpasses would be beneficial, but I didn’t anticipate such a dramatic impact,” stated Matthew Marcelino, a co-author of the study and ecologist at the University of Vermont (UVM). “In particular, when we excluded mountain-dwelling amphibians-primarily spring peepers-we observed a 94% reduction in mortality within the areas equipped with these structures.”

Understanding Amphibian Vulnerability

Globally, amphibian populations-including frogs, salamanders, and newts-are experiencing unprecedented declines. Factors such as the deadly chytrid fungus have decimated many species, while habitat destruction and climate change further threaten their survival. Recent statistics indicate that over 40% of amphibian species are currently at risk of extinction, making conservation efforts more urgent than ever.

In Vermont, these creatures are vital components of local ecosystems. They help control insect populations like mosquitoes, serve as prey for larger animals, and facilitate nutrient cycling within their habitats. Their sensitivity to environmental changes makes them excellent indicators of ecosystem health. Many amphibians in the northeastern United States spend most of their lives underground or in dense forest soils, emerging only during specific times of the year to breed. During spring, warm, rainy nights trigger mass migrations from upland forests to breeding ponds and wetlands.

“Typically, this migration occurs between late March and early April,” explained Brittany Mosher, a co-researcher and quantitative ecologist at UVM. “Multiple species often congregate in the same breeding sites, with hundreds or even thousands moving simultaneously. It’s a spectacular yet vulnerable event.”

Roads: A Critical Threat to Amphibian Survival

One of the most immediate dangers amphibians face during migration is vehicular traffic. Roads dissect migration corridors, causing thousands of amphibian fatalities annually. Due to their small size and slow movement, frogs and salamanders cannot cross roads quickly-unlike larger animals such as deer-making them especially vulnerable to being hit by vehicles. During peak migration periods, the mortality rate can reach staggering levels, with some studies estimating that over 70% of migrating amphibians perish on roads in heavily trafficked areas.

In response, local conservation groups and researchers collaborated to install two amphibian underpasses beneath a one-mile stretch of road in Monkton, Vermont, about 20 miles south of Burlington. These structures, built in 2015, are designed to facilitate safe passage for migrating amphibians, reducing roadkill and supporting population stability.

The underpasses consist of two four-foot-wide concrete tunnels, equipped with guiding barriers to direct amphibians into the safe passageways. During the spring of 2016, wildlife cameras installed by the Lewis Creek Association recorded over 2,200 amphibians using these tunnels. Interestingly, other animals, including raccoons, bears, bobcats, porcupines, snakes, and various bird species, also utilized these crossings, highlighting their broader ecological benefits.

Evaluating the Effectiveness of Wildlife Crossings

Recent research conducted by UVM, Vermont’s Department of Natural Resources, and citizen scientists employed a before-and-after study design to assess the impact of these underpasses. This approach involved monitoring amphibian road mortality over a span of 5 years prior to construction (2011-2015) and 7 years afterward (2016-2022). The study focused on three zones: the treatment zone with underpasses, a buffer zone adjacent to the treatment area, and a control zone located away from the infrastructure modifications.

During spring migration surveys, teams recorded every amphibian crossing, noting species and mortality. Initially, over 5,200 amphibians were observed, with a significant proportion-nearly 70%-of spring peepers and salamanders found dead on the roads. Post-installation data revealed a dramatic decline in mortality rates within the treatment and buffer zones, with reductions of approximately 73% for certain species.

While the decrease in mortality among spring peepers was not statistically significant, the overall trend indicated substantial benefits for ground-dwelling amphibians. The data suggest that the tunnels effectively facilitated safe passage, preventing animals from being displaced to the edges of barriers and reducing fatalities. The study also emphasized that the structural design-such as tunnel height, width, and materials-plays a crucial role in ensuring their success.

Implications for Future Conservation Strategies

According to Marcelino, these findings provide compelling evidence that wildlife underpasses are a practical and effective conservation tool. They demonstrate that with proper design and strategic placement, such structures can significantly mitigate road-related amphibian mortality. He advocates for transportation agencies to incorporate these crossings into future road planning and maintenance projects, emphasizing that investing in such infrastructure benefits both ecosystems and human safety.

“Conservation requires a dedicated approach,” Marcelino remarked. “When we commit resources and carefully implement these solutions, the ecological gains are profound. Amphibians are delicate yet vital creatures-beautiful and often overlooked, but essential to healthy ecosystems. Protecting them is a responsibility we should all share.”