Biologists believe it is the first time such an experiment has been attempted with mountain lions, with scientists noting that it was worthwhile to try to keep the kittens in their natural habitat and to learn more about the species' behavior.
The two kittens -- a female dubbed P-91 and a male dubbed P-92 -- were discovered July 7 in the Simi Hills south of Simi Valley while their mother, P-67, was away from the den. Biologists subsequently located the kittens' 2 1/2-year-old mother dead, and realized the kittens would not be able to survive without a mother.
The California Department of Fish and Wildlife's statewide mountain lion researcher, Justin Dellinger, suggested that the kittens could be fostered with another mountain lion, P-65, who had given birth to three kittens -- P-88, P-89 and P-90 -- that had been found the day before in the Santa Monica Mountains.
3 mountain lion kittens born in Santa Monica Mountains
"These five kittens were all approximately the same age, which meant we had this unique opportunity to attempt fostering and give these kittens a chance to live in the wild,'' said Jeff Sikich, a wildlife biologist who leads fieldwork on the mountain lion project. I had tried this with black bears on a previous research project and it had worked, but situations can vary for different species and individuals. I wasn't sure if it would prove successful with these mountain lions.''
Biologists rubbed urine from one of P-65's kittens on the orphaned kittens so they would smell like her offspring, but discovered that she had moved her den -- a normal event for mountain lions -- and left the two orphaned kittens behind.
The kittens temporarily went back to the Los Angeles Zoo, where they had been temporarily housed before the foster attempt, and then were moved to the Southwest Wildlife Conservation Center in Scottsdale, where they will spend the rest of their lives. They're now about three months old and are reported to be showing typical wild cat behaviors, including stalking, wrestling and climbing.
The kittens were among 13 born to five mountain lion mothers between May and August, marking the first time that many mountain lion dens had been found within such as short period of time during an 18-year study by the National Park Service of mountain lions in and around the Santa Monica Mountains.
"Our shared goal for this project all along was to keep the kittens in the wild and, although the new mother did not accept them, we gained considerable knowledge from this experience,'' said Christine Thompson, a regional biologist with the California Department of Fish and Wildlife. "We were also able to successfully place the healthy kittens in a new home. Many thanks to go to NPS (National Park Service), Los Angeles Zoo and the Southwest Wildlife Conservation Center for their dedicated efforts.''
Biologists suspect that the kittens were fathered by P-78, who is now living in the Santa Susana Mountains and had been tracked traveling with the kittens' mother over a period of multiple days earlier this year. He was the first collared animal in the study to spend a considerable amount of time east of Highway 5 in the San Gabriel Mountains.
Mountain lion apparently struck, killed trying to cross 101 Fwy in Calabasas
P-67 was originally tagged as a kitten herself in 2018, also in the Simi Hills, in a den belonging to adult female P-62. The father of P-91 and P-92 is suspected to be P-78. Biologists tracked the two of them traveling together over a period of multiple days earlier this year.
A necropsy on the orphaned kittens' mother showed that she was found with no food in her stomach, was relatively thin and had evidence of intestinal disease, according to the National Park Service. She had been exposed to five different anticoagulant rodenticide compounds and a highly potent rodenticide that provides a lethal dose to rodents in a single feeding, and her presumptive cause of death was septicemia -- a bacterial infection -- possibly secondary to enteritis, researchers said.
"A contributing factor may have been that she was young and stressed by having kittens,'' Sikich said. "She was a good mother and she didn't abandon them. She kept on coming back to the den and nursing them even in her likely poor state of health.''
On Tuesday, Gov. Gavin Newsom signed a bill introduced by Assemblyman Richard Bloom, D-Santa Monica, to restrict the use of certain rat poisons -- second-generation anticoagulant rodenticides -- that have been linked to the deaths of mountain lions and other wildlife.
The National Park Service recently reported that a male mountain lion, P-76, that was collared last November in an urban neighborhood in Northridge and subsequently found dead in January and a bobcat discovered in a residential neighborhood of Agoura Hills had died directly from the effects of anticoagulant rat poisons.
P-76 was the sixth collared mountain lion to die of coagulopathy and the third in the last two years, and researchers have documented the presence of anticoagulant rodenticide compounds in 26 of 27 local mountain lions that have been tested, including a 3-month-old kitten.
CA tightens rules on rat poisons that kill mountain lions, birds, endangered wildlife