Scientists who track cougars by radio collar say they are finding strong evidence of a grim reality: the big cats are becoming increasingly isolated in the Santa Ana Mountains as connections to other wild lands disappear.

A new study reveals the fate of one cougar family trying to cope with increasing development around their home ranges.

The mother mountain lion died soon after she was fitted with her collar for unknown reasons.

Of her two male cubs, one was shot by a poacher while trying to make use of a wildlife corridor.

The other survives in the northern Santa Ana Mountains, but his movement pattern suggests he has been probing the urban edges of the range, as if searching for a way out.

The mountain lion study, to be published this month in the scientific journal, Conservation Biology, offers a living portrait of a deadly problem for Southern California’s big cats.

As development intensifies, the connections to other habitat areas become more tenuous, then vanish completely.

“It really points out how limited has been the connectivity at very large scales,” said Scott Morrison, science director for the Nature Conservancy’s California chapter.

Using radio-collar tracking of the three lions beginning in 2005, plus data gathered in other cougar studies in the Santa Ana Mountains over decades, the scientists offer a grim picture of the wide-ranging lions trying to cope with a rapidly shrinking world.

Click to see larger map.

“It’s going to be ongoing vigilance that is going to keep the habitat functioning for these species,” Morrison said.

He and the other scientists, however, try to strike a hopeful note. The way out for the lions, they say, is already a matter of established conservation policy in Southern California: cooperative habitat agreements called Natural Communities Conservation Plans.

A product of the 1990s habitat wars between environmental groups and developers, the plans attempt to bring landowners, developers, activists, scientists and regulators together to carve out nature reserves before the areas around them are developed.

Such plans have produced two large nature reserves in Orange County, with plans completed or under way in neighboring counties.

The study focuses in part on the Tenaja corridor, a natural connection between the Santa Ana Mountains and the Santa Rosa plateau just west of I-15 in Riverside County.

Keeping such corridors natural, or restoring them to a natural state, is a big priority for conservationists as Southern California continues to be developed. Animals move across such corridors, while plant seeds are carried through them; when the connections are severed, populations trapped inside habitat fragments can dwindle and disappear.

“What really opened up our eyes about these issues was that one of them was shot by a poacher right in the middle of the Tenaja corridor — here in this wildlife linkage we’ve been trying to protect for over 10 years,” Morrison said.

The Nature Conservancy has been trying to purchase enough land along the corridor to keep it open for mountain lions and other creatures.

“It’s disconcerting when it takes over 10 years and we still haven’t completed a three-mile stretch,” Morrison said. “We need to ratchet up our best efforts.”

Though a useful tool, buying up parcels by itself won’t solve the problem of vanishing wildlife corridors in Southern California, he said.

“We can’t rely on that alone,” Morrison said. “We also need to have as much support from land use planning and policy as we can bring to bear on the issue.”

Wise use of the NCCP process, and linking the various NCCP reserves in Southern California together with viable corridors, could make the difference between existence and extinction for the lions that remain in the Santa Ana Mountains.

Even with corridors designed for wildlife, it can be difficult to tell whether they work.  The sole survivor of the radio-collared lion family seems shy about using a wildlife corridor at Coal Canyon that runs beneath the 91 Freeway.

“The third one is still out there,” Morrison said. “That’s his home range.”

(Motion-triggered camera photo of a mother lion courtesy of UC Davis Wildlife Health Center and Donna Krucki, though not the one in the recently published study; the points of light in background are the eyes of her two cubs.)

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