Mountain lions may be playing an unexpected role in making California roads safer for drivers by influencing deer behavior, a recent study suggests. Researchers found that the presence of these large carnivores is associated with a significant decrease in vehicle collisions with deer.
The study, published in Current Biology, indicates that in areas frequented by mountain lions, the likelihood of a vehicle colliding with a deer dropped by 67%. This effect is attributed to mountain lions, also known as pumas or cougars, causing deer to avoid roads and instead move into more remote habitats.
"We found that large carnivores can make roadways safer through their effects on prey behavior and space use," said lead author Justin Suraci of Conservation Science Partners. "Deer alter their use of both space and time where pumas are present, overlapping less with roads and reducing activity at night, when some of the most dangerous collisions occur."
Deer are also 86% more likely to occupy remote areas away from roads when mountain lions are present, contributing to an estimated 76% reduction in total expected collisions over a five-year period. A 2024 report from UC Davis's road ecology center estimated that up to 100,000 deer are struck by vehicles annually on California roads.
To reach these conclusions, researchers analyzed camera trap data from over 500 locations and tracked GPS collar data from approximately 60 mountain lions across the Olympic Peninsula in Washington. While the study was conducted in Washington, Suraci anticipates similar outcomes across mountain lion habitats in the western United States.
Mark Elbroch, an ecologist for Panthera and a co-author of the study, highlighted the broader benefits of large carnivores. "When we talk about pumas, we often focus on the risks they pose," Elbroch stated. "But we rarely stop to consider the many ways they benefit us as well."
Despite these ecological benefits, mountain lions themselves face threats from human activities. Vehicle strikes are a significant mortality factor, contributing to the species being listed as endangered under the California Endangered Species Act earlier this year. Habitat loss, fragmentation by roads and development, vehicle collisions, and other risks threaten their long-term survival.
Conservation efforts are underway to improve road safety for both wildlife and humans. For instance, a wildlife crossing on California's Highway 17 has seen about 1,000 animals per year use the tunnel, including various species like mountain lions, deer, bobcats, and skunks. Suraci suggested that such structures can have compounding benefits, not only by providing safe passage for deer and reducing collisions but also by promoting movement for predators like mountain lions, which in turn can further influence deer behavior and reduce road dangers.