Too many deer? Get cougars, scientists say

Posted on: July 21, 2016 | Bob Frye | Comments

Mountain lion2Some people would thrill to see a mountain lion in the eastern United States, some scientists say. And they could help control deer, they add. But what of the costs?

Defensive driving, i.e. staying alert, that’s one way to perhaps minimize deer-vehicle collisions.

Might cougars be another?

Some researchers think so.

A group of scientists recently published a paper in a scholarly journal suggesting that not only could eastern states – like Pennsylvania – house mountain lions again, but perhaps should, as a way of controlling white-tailed deer populations.

In an article published in “Conservation Letters,” the authors write that deer-vehicle collisions have increased in conjunction with the decline in populations of top carnivores. There are about 1.2 million vehicle collisions each year, they said. The result: 29,000 injuries and more than 200 human deaths.

That makes deer “the most dangerous large mammal in North America to humans.”

Predation is the answer, they added. The scientists developed a model looking at projected increases in deer numbers, possible cougar densities and deer-per-cougar kill rates.

In the end, they determined that re-colonizing mountain lions could reduce deer vehicle collisions in the eastern United States by 22 percent, preventing 21,400 human injuries, 155 fatalities and $2.13 billion in costs over 30 years.

“Large carnivore restoration could provide valuable ecosystem services through such socio-ecological cascades, and these benefits could offset the societal costs of co-existence,” reads the report, written by lead author Sophie Gilbert of the University of Idaho department of fish and wildlife sciences.

The scientists admit there would be challenges. Large carnivores are “highly polarizing.”

Most concerns, though, are more perception than reality, they argue.

Cougars killed 21 people and attacked 152 in the United States and Canada between 1890 and 2008, they wrote.

“Yet we estimate cougars would indirectly save far more people from death (5 per year) and injury (680 per year) by reducing deer-vehicle collisions than they would likely directly kill (< 1 per year) or injure (~5 per year). However, fear of cougar attacks may reduce enjoyment for some outdoor recreationists,” they wrote.

Concerns about livestock depredation and attacks on pets are also likely overblown, they added.

Of course, there’s the hunting question, too.

Deer, the authors admit, have high value to hunters and wildlife watchers. But if hunter numbers continue to decline – and a larger and larger portion of the burden for controlling deer is left to a smaller and smaller group to carry – the cost of large carnivores goes down, they added.

“It is likely that livestock producers, rural residents that fear cougars, and hunters bear the brunt of the costs of large carnivores, while agricultural producers, home-owners with landscaping, drivers, local governments, and insurance agencies reap the majority of benefits,” the study authors wrote.

“Understanding and potentially compensating for inequalities in allocation of costs and benefits could improve conservation outcomes for large carnivores such as cougars as they recolonize.”

The full report is available here.

Bob Frye is the editor. Reach him at 412-838-5148 or See other stories, blogs, videos and more at

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Bob Frye is a storyteller with a passion for all things outdoors. He hunts, he fishes, he hikes, he camps, he paddles, backpacks and snowshoes depending on the season. If he’s not an expert at anything, it’s because he’s passionate to try a little bit of everything.