As mountain lions in California slowly make their way back from the near-extinction, they continue to face myriad challenges. But for the majestic pumas, no challenge is greater than the threat of man.

A new survey of mountain lion populations in Southern California looked at the leading causes of death for the powerful cats: A majority come at the hands of humans -- vehicle collisions, depredation permits, illegal shootings, public-safety removals and human-caused wildfire.

The new study was published in the journal PLOS ONE.

Compounding these threats is the mountain lion's shrinking habitat -- one increasingly bisected by large and dangerous highways.

Most of Southern California's mountain lions are found among the hills between Los Angeles and San Diego, but populations are increasingly fragmented and cut off from each other, unable to cross the I-15 thoroughfare connecting San Bernardino, Riverside and San Diego Counties.

"Nowhere in the U.S., outside of the endangered Florida panther, have mountain lion populations been documented that are this cut off and with survival rates this low," lead study Winston Vickers, an associate veterinarian with the UC Davis Wildlife Health Center at the UC Davis School of Veterinary Medicine, said in a press release. "This means that the odds of an individual animal making it across I-15, surviving to set up a territory, successfully breeding, and then their offspring breeding so the genes are spread throughout the population is harder to have happen naturally than one would expect."

Because of the isolation, some groups are increasingly interbred -- adding genetic health problems to list of threats facing the species.

In the last 13 years of monitoring Southern California's pumas, researchers have witnessed only one lion cross I-15. A male lion, M86, found a mate and produced four kittens. One was killed by a car, another poisoned, and a third was captured for becoming too familiar with humans. The fourth mated. She successfully raised two kittens, only one of which is confirmed to be alive.

"So all the genetic hopes of this population may be pinned on this one animal, F126 -- a female we know is circulating," Vickers said. "Given the odds of that female producing kittens, and those kittens producing kittens, it will take generations and generations to see if his effort, M86's, in crossing the road was worth it."

Some have proffered the idea of relocating the population, as has been done with pumas in South Florida. But Vickers says the more appropriate solution is to simply improve conservation efforts and construct overpass connections bridging isolated populations.

Whatever conservationists decide to do, however, Vickers says they need to do it now -- and fast.

"This population has one foot on the banana peel and one foot on the edge," Vickers said of Santa Ana pumas. "Whatever we can do, we should do. Other populations are going the same direction, they're just not as far down the road."