What’s one simple, inexpensive way to make driving safer?

Letting big predators live.

If mountain lions returned to the eastern United States, say researchers, their predatory habits would literally get white-tailed deer off the road, reducing collisions between drivers and deer by 22% over the next 30 years.

That would translate into 21,400 averted injuries, 155 human deaths, and more than $2 billion in savings—a pretty good return on letting nature take its course.

The findings, published in the journal Conservation Letters and led by biologists Sophie Gilbert of the University of Idaho and Laura Prugh of the University of Washington, are based on the experience of drivers in western South Dakota, where mountain lions returned in the 1990s after being extirpated a century earlier.

Deer collisions there have declined, and little wonder: in the average mountain lion’s six-year life span, they consume some 259 white-tailed deer. There’s no reason to think it would be different in the east, where mountain lions are slowly making their return, and where rich forest habitat exists in almost all of their historical range. (The heavily farmed and fragmented states of Illinois, Maryland, Delaware, and Rhode Island would, alas, be exempt from these benefits.)

The mountain lions’ return has been controversial: while conservationists and ecologists speak of the benefits they provide as apex predators—namely regulating ecosystems and reducing deer populations that swell in the absence of natural controls—many people fear attacks on pets, livestock, and humans.

But as documented in California, where thriving mountain lion populations cause few problems even in heavily-populated areas, the big cats are as happy as we are to avoid conflict. And though coexistence does come at a cost—vigilance, habitat protection, and, yes, the infrequent attack—it might be balanced by the benefits.

While it could take decades for mountain lions to fully reoccupy their ancestral eastern homes, the new findings have a more immediate implication. Other large predators, such as bear and coyote, also help control deer populations and might indeed make roads safer, said Prugh. The same goes for another controversial returnee.

“We next hope to analyze data on deer-vehicle collision rates in areas where wolves have recently recovered,” she says. —Brandon Keim | 20 July 2016

Source: Gilbert et al., “Socioeconomic Benefits of Large Carnivore Recolonization Through Reduced Wildlife-Vehicle Collisions.” Conservation Letters. doi: 10.1111/conl.12280

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