The ever-increasing population of white-tailed deer in the Bay watershed and the resulting human health and environmental problems could be reduced without resorting to hunting or any other human intervention, according to some wildlife scientists.

The remedy? Allow the return to the Eastern United States of one of the animal species that helped keep deer populations in check for eons: cougars.

Cougars, also known as mountain lions, once roamed all of North America. But they were hunted to the point that until recently, they were found only in the west -- except for a close relative, the Florida panther, which lives in the southern part of the sunshine state.

According to a paper published online recently in Conservation Letters, the journal of the Society for Conservation Biology, if cougars could be reestablished in the East, they would kill enough deer to reduce deer-motor vehicle collisions by 22 percent.  The reduction could well be greater, the authors noted, because to be conservative, they assumed that in the East cougars would be restricted to heavily forested areas. But in the West the big cats are known to prey as well on deer in the suburbs, thereby also reducing deer and crashes in those areas.

Over 30 years, the authors project, cougars would prevent 21,400 human injuries and 155 fatalities, and save $2.1 billion in insurance and other accident-related costs.  A single cougar can kill 260 deer over its normal six-year lifespan, the paper estimates.

In addition to their role in car crashes, deer host the Lyme disease pathogen, damage forest ecosystems and bedevil gardeners.

Eastern cougars were thought to have been wiped out by the early 1900s, but western cougars – thought by many to be the same species – have begun to move east, recolonizing Wisconsin, Missouri and other portions of the Midwest in the past 25 years. Cougar sightings have been reported as far east as Connecticut.

The study, led by Sophie Gilbert, an assistant professor of fish and wildlife sciences at the University of Idaho, acknowledges that cougars kill not only deer. Pets, farm animals and sometimes people can also be their prey.  However, the study it estimates that 10 times as many human lives would be saved due to reductions in deer-motor vehicle accidents than lost due to mountain lions.

“The most important thing about this work is that it could help people understand that carnivores have some real benefits to offer human populations, in addition to costs that are often discussed,” Gilbert said in a University of Idaho press release.