LOS ANGELES - Morning commuters in Los Angeles were likely startled, if not downright terrified, when a young mountain lion recently strode onto Interstate 405 and was killed by oncoming traffic.

But biologists who have spent a decade studying the lions living in the nearby Santa Monica Mountains say the cat was simply searching for a home. While mountain lion populations are healthy across California, the situation is becoming increasingly desperate for the isolated population in the Santa Monica Mountains.

Lions need as many as 100 square mile each as territories, but the estimated 10 cats in this 275-square mile mountain range are hemmed in by network of freeways, suburbs and the Pacific Ocean.

Without an easier way to connect to the state's larger mountain lion population, biologists say those that live amid the urban sprawl of the nation's second largest city will go extinct from inbreeding.

"It's a very unique situation," said Tim Dunbar, the executive director for the Mountain Lion Foundation. "Usually our urban centers radiate out so there are mountain lions along the edges. What happened in this case is they've sort of been ringed in."

In 2002, the National Park Service decided to study this rare group of urban lions to get a better understanding of how the cougars navigate living in such a setting. Since then scientists have trapped and radio collared 21 lions, allowing biologists to monitor their movements, their feeding, even their attempts to breed.

Mountain lions are one of the most widespread carnivores in the world with a historical range from Alaska to Tierra del Fuego, Chile. They are still found widely across the West and Southwest and even in south Florida.

The straw-colored cats are solitary and elusive animals. And despite living against an urban setting, biologists say they were surprised to discover the LA lions still behave as if in the wild, feeding largely on mule deer. Male lions can be as long as 9 feet from head to tail and weigh 220 pounds and both sexes need a lot of territory. Male lions spend their days roaming for food, for females with which to mate and for trespasser lions to kill.

Of the group of 21 lions that have been collared over the years in the Santa Monica Mountains few have survived. Only one male is known to have come from the outside, from the Simi Hills across the 101 freeway into the Santa Monicas, this in 2009, bringing fresh genes with him. Biologists estimate there are currently about 10 of the big cats in the encircled zone.

Jeff Sikich, an ecologist with the National Park Service who has been studying the lions, called the situation "dire." Numerous local, state, federal and non-profit organizations are working to identify areas to build wildlife crossings to help the lions get across freeways to open space north of Los Angeles but it will likely be years before they're complete.

"There's really nowhere for them to go," Sikich said. "They're almost trapped in this island of habitat."

Weaker lions can be killed by those more dominant when they can't get out. In one case, the male responsible for a litter of four killed three of his offspring when they were unable to find their own territory.

Others died from eating smaller animals contaminated with rat poison or, like the 15-month-old lion killed on the freeway recently, died trying to leave the mountain range. Many of the Santa Monica lions died trying to cross highways.

"They're coming up to the freeway, turning around and going into residential areas, turning around and are taken to the extreme edges of our mountains and eventually the adult male will find them and kill them," Sikich said. "Mountain lions are solitary animals and a male lion will constantly defend its territory."

In the hopes of preventing the group's extinction and for public safety reasons, the California Department of Transportation has been working with the Santa Monica Mountains Conservancy and the Park Service on finding wildlife crossing sites along the freeways. Such passage would allow wildlife to move safely from the Santa Monica Mountains to open space in the Santa Susana Mountains and Los Padres National Forest.

Experts say the radio collars have shown them where the lions are most likely to try and cross the freeways and while signage isn't an option with animals, biologists say the lions are adept at finding crossings once they are in place.

The agency has applied for a multi-million dollar federal grant to pay for a $9.4 million project for fencing and a 13 foot by 13 foot tunnel under 101. Since wildlife typically crosses at night, the underpass would also be available for hikers and pedestrians during the day, said Barbara Marquez, senior environmental planner at Caltrans

Still, even if the project is funded, it will take years and the lions would still face two other freeways before getting to the rocky expanses of the Los Padres National Forest.

Officials are also looking into installing fencing near the site of the accident on the 405 to herd wildlife toward safer crossings as well as widening a bridge to include a protected area for wildlife.

"This is something that needs to happen," said Christy Brigham, chief of planning, science and resource management with the Santa Monica Mountains National Resource Area. "There's absolutely no question that if we don't maintain the connectivity between the Santa Monica Mountains and the rest of undeveloped Southern California and the state as a whole, the mountain lions will go extinct in the Santa Monicas."