Pumas Cut Deer Crashes 67% in Washington Study

Mountain lions might be your unexpected road safety partners, and scientists just proved it with hard numbers.

A groundbreaking study on Washington's Olympic Peninsula tracked 59 GPS-collared pumas and deer movements at 503 camera sites over five years. The results stunned researchers: when mountain lions were nearby, deer-vehicle crashes dropped by 67 percent, preventing an estimated 76 percent decline in total collisions.

During the study period from 2020 to 2025, deer caused 92 percent of the 953 wildlife crashes on the peninsula. Those accidents killed two people, injured over 80 others, and racked up $14.7 million in vehicle repairs and medical costs.

The secret lies in how deer respond to their natural predators. When pumas prowled nearby, deer abandoned dangerous "edge" habitats like roadsides and town outskirts, heading deeper into forests instead. This makes perfect sense given how mountain lions hunt.

"They're ambush predators," explains study co-author Justin Suraci, an ecologist with Wildlife Conservation Science. "They prefer edgy, moderately fragmented habitats like roads cutting through forests. It gives them opportunity to conceal themselves and attack deer foraging just outside the forest."

The big cats changed deer behavior in another crucial way. Deer became more active during daylight hours and less active at night, when the most dangerous collisions happen. Scientists believe this shift also stems from avoiding pumas, who primarily hunt after dark.

The research team partnered with five Native American tribal nations who shared data from their wildlife monitoring programs. This collaboration revealed patterns that could apply far beyond Washington state, since pumas roam throughout the Americas.

The Ripple Effect

This finding adds important context to debates about coexisting with large predators. While mountain lions pose real challenges including livestock losses and safety concerns, they're also delivering measurable benefits that communities are only beginning to understand.

One 2022 study found that maintaining daylight saving time year-round would prevent 33 human deaths and save $1.19 billion in collision costs annually. But pumas might offer similar protection naturally, free of charge, simply by being present in the ecosystem.

"This is useful for anywhere you have dense forest, roads and then more forest," says Fraser Shilling, director of the Road Ecology Center at UC Davis. The ecosystem service pumas provide could be working silently across their entire range.

Scientists are just starting to quantify the full value these apex predators bring to human communities, and road safety appears to be only one piece of the puzzle.