A study published in the journal Current Biology has found that car accidents involving deer in the US could fall by as much as 76% in areas with healthy cougar populations, as the big cats' presence deters deer from foraging near roads and forest edges. This matters because deer-vehicle collisions have risen steadily since the 1970s, killing more than 200 people last year, and the findings suggest restoring predator populations could offer a natural, low-cost way to improve road safety while also highlighting an overlooked benefit of human coexistence with large carnivores.

Researchers, including lead author Justin Suraci of Conservation Science Partners, analysed data from over 500 cameras alongside a year of deer-related crash data on Washington's Olympic Peninsula, where a cougar monitoring programme has run since 2018. They found deer were 15% more likely to avoid roads where cougars were known to hunt, 86% more likely to stay in wooded areas, and more active during daylight hours, collectively cutting collisions by more than three-quarters over a five-year period compared with areas with fewer cougars. Cougars, also known as mountain lions or pumas, once ranged across much of North America but are now largely confined to western US states and small parts of Florida, while deer numbers have surged due to reduced predation, hunting limits and habitat expansion.