The four female kittens are about 5 weeks old and are the first litter that has been found in the Simi Hills, a small area of habitat between the Santa Monica and Santa Susana mountain ranges just north of Los Angeles.
Researchers have added the four kittens to their ongoing study of mountain lions in the area. Their mother is a mountain lion researchers have been tracking since January.
Researchers visited the kittens while their mother was away last week, taking tissue samples, conducting a general health check and marking them with ear tags, which will allow them to keep track of their movements as they grow up.
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It's the 15th den the researchers have marked as part of their study of mountain lions in the region.
Biologists have been studying the cougars to determine how they survive in fragmented wilderness amid metropolitan sprawl. Each member of the species, especially males, requires a very large home territory, and young cats face difficulties dispersing.
Jeff Sikich, biologist for Santa Monica Mountains National Recreation Area, said the spot where the kittens were found in the Simi Hills is "a critical habitat linkage between the Santa Monica Mountains and larger natural areas to the north."
"We are very interested to learn about how they will navigate the fragmented landscape and whether they will remain in the Simi Hills or eventually cross one or more freeways to the north or south," he said.
Except for the kittens' mother, researchers say every mountain lion they've tracked in the Simi Hills has crossed either the 101 freeway to the south or State Route 118 to the north.
Since 2002, 18 mountain lions have been killed on freeways and roads in the region, most recently a 5-year-old female earlier this year.
The area's most well-known mountain lion, P-22, has become famous for having somehow crossed freeways to take up residence in sprawling Griffith Park in the middle of Los Angeles.