THOUSAND OAKS, Calif. — A litter of blue-eyed mountain lion kittens has been discovered in Southern California's Santa Monica Mountains, but researchers believe they are the product of inbreeding, a serious problem for the population isolated by a major freeway.

The National Park Service said Tuesday the two males and two females appeared to be in good health when they were checked by biologists, who took tissue samples and placed ear tags on the kittens, now known as P-70, P-71, P-72 and P-73.

The service is studying how cougars survive in fragmented habitat.

The kittens' mother is 8-year-old P-19 and the father is believed to be P-56, her grandson.

A wildlife bridge over U.S. 101 has been proposed to let the big cats move between the Santa Monicas and wilderness to the north.