Image caption Cougars are moving east from their traditional western habitats

The American mountain lion or cougar is now re-populating parts of the US, scientists say.

Their numbers had plummeted in the last 100 years because of hunting and a lack of prey.

Writing in the Journal of Wildlife Management , researchers say the cougar is now spreading far outside their traditional western habitats.

But they say the return of the big cats raises important questions about how humans can live with these predators.

Image caption The cougars' decline was caused by hunting and a decline in their prey

Such has been the decline of the cougar in some parts of the United State that the US Fish and Wildlife service declared the eastern cougar extinct just last year.

For decades mountain lions were seen as a threat to livestock and humans and many States paid a bounty to hunters for killing them.

Their habitats were restricted to the areas around the Black Hills of Dakota. But in the 1960s and 70s the animals were reclassified as managed game species, so hunting was limited and numbers started to grow.

They are very fleeting animals they're solitary and they don't like people Michelle LaRue, University of Minnesota

Anecdotal evidence indicates that mountain lions started to spread far and wide during the 1990s - this perspective was confirmed last June when a young male was hit by a car and killed in Connecticut.

Genetic analysis indicated that the animal originated from the Black Hills and had travelled approximately 2,900km (1,800mi) via a number of States.

Now researchers have published the first scientific evidence that cougars have returned to the mid-west and are now to be found as far south as Texas and as far north as the Canadian provinces of Ontario and Manitoba.

They say that limits on hunting and the return of elk and mule deer that cougars prey on have been key to increasing the overall population which is now said to number around 30,000.

And as the populations have grown, the territorial instincts of the big cats have forced them to conquer new ground. Michelle LaRue from the University of Minnesota, is one of the authors of the paper.

"What's happening is that, as the young males are moving out of the areas they were born in, they are coming into contact with other young males and they don't have anywhere else to go so they're kind of being forced out of these western populations and into these areas of vacant habitats in the mid west," she said.

The team used recorded sightings that had been verified by wildlife professionals as well as carcasses, DNA evidence and cases of attacks on livestock across 14 State and provinces. And the scientists believe the spread of the cougar might continue.

"I would assume that with the continued management practices that have allowed for the rebound, cougars have the potential to continue to move eastward into areas of available habitat," said Michelle LaRue.

Many researchers are concerned that the spread of the mountain lion will inevitably bring them into conflict with humans. Other species such as bears have run into trouble thanks to their taste for human food. Ms LaRue said that cougars are very different.

"They are very fleeting animals they're solitary and they don't like people, they like to be in remote rugged wilderness areas, I say it's a lot less likely than they'll become dependent on trash like bears."

"If you were in the woods with a cougar and it saw it you wouldn't even know it, it would run before you even knew it was there."