American cougars are moving back into their native Midwest habitat after nearly going extinct last century, researchers reported Thursday.

It turns out they're doing it largely on their own, without the help of humans, by gradually finding corridors out of their western enclaves.

The species seems to have found a way "to naturally recolonize the Midwest," said Clay Nielsen, co-author of a study published in Journal of Wildlife Management, released Thursday.

Three breeding populations have been found in western parts of Nebraska, North Dakota and South Dakota, he added, and probably started dispersing east from the population in the Black Hills of South Dakota.

The researchers studied 178 confirmed cougar sightings over the last 20 years to reach that finding. They also found that sightings have increased steadily over time. The most sightings, 67, have been in Nebraska.

Some of the 178 sightings were certainly repeats of the same cougar, Nielsen acknowledged, but the researchers were still confident about their conclusions because 56 of the sightings were carcasses found across the Midwest, said Nielsen, a forest wildlife assistant professor at Southern Illinois University. 

Journal of Wildlife Management

The areas shaded green are existing cougar habitat, including populations in Nebraska and the Dakotas. The black dots are cougar sightings from 1990 to 2008.

The most famous sighting was a male cougar that made his way 1,500 miles from the Black Hills to Connecticut last year before being hit and killed by a car. 

American cougars, also known as mountain lions or pumas, had been restricted to the West, as well as a few in Florida, after being hunted as a pest across the East and Midwest in the first half of the 1900s.

Starting in the 1960s, their status changed from "bountied predator" that hunters could legally target to a "managed game species" with certain protections.

In the West, where up to 35,000 cats are spread across 14 states, cougars are not listed on the federal Endangered Species Act because that issue is considered on a statewide basis, Tim Dunbar, head of the Mountain Lion Foundation, told msnbc.com. 

The group is worried that any resurgence will be undermined by what it considers lax state policies. 

Chuck Anderson / Colorado Parks & Wildlife

These three cougar kittens were photographed during a research project in southeast Wyoming while the mother watched from about 100 yards away.

"Decisions made by Wyoming, South Dakota, and now Nebraska are placing that specific lion population at risk," Dunbar said. "Also it seems that several Midwestern lawmakers are trying to make it legal to kill any lions that might survive to make it to their states." 

The researchers said part of the challenge is in reassuring a public that has "been living without large carnivores there for nearly a century." 

Mountain lion shot dead in Santa Monica courtyard

"The risk of being attacked by cougars is very, very, very low," Nielsen insisted. "Man has much more to fear from fellow humans and many other animals than cougars in the Midwest."

In fact, he says, simply spotting a cougar is extremely rare. "The odds of a sighting are a little more likely than winning the lottery, but not a whole lot."

More content from msnbc.com and NBC News:

• Troubling sign for housing recovery: Foreclosures jump
• Metallica helps FBI try to track down killer of Virginia Tech student
• Blinded soldier aims for Paralympic Games in London
• Video: Caught on camera: Toddler tossed during car chase

Follow US News on msnbc.com on Twitter and Facebook