First mountain lion to die of mange had five different rat poison chemicals in her system

While scientists are sadly accustomed to rangy mountain lions killed by cars when they try to cross roadways like the 101 Freeway in San Fernando Valley, this year a cougar was killed by a disease far from the freeways, a state agency reported on Monday, Sept. 26.

P-65, a five-year-old adult female, is the first mountain lion in Southern California to perish from mange — a common skin disease caused by a mite parasite — during the 20 years of U.S. National Park Service (NPS) research into local cougars. Scientists found her body on March 4, 2022, near a mountain stream in the central Santa Monica Mountains.

“All of these animals recovered from their mange disease, as best as we could tell from remote camera photos or later examination,” said Jeff Sikich, a wildlife biologist in the park, in a prepared statement. Sikich and other NPS biologists working in the 150,000-acre Santa Monica Mountains National Recreation Area were unaware of P-65’s condition until after she died.

NPS biologists say the lion’s immune system was compromised by the effects of rat poison which is often left outside by homeowners or institutions such as schools or local governments. Most likely, the lion ate a dead animal that had eaten a rat or squirrel that ingested the rat poison.

A necropsy found five “anticoagulant rodenticide” compounds in P-65’s liver: brodifacoum, bromadiolone, difethialone, chlorophacinone, and diphacinone. She also was exposed to bromethalin, a neurotoxic rodenticide, the NPS reported.

Rodenticides travel up the food web. Their fatal effects have been associated with causing immunodeficiency in larger animals such as bobcats and mountain lions. That leaves big cats highly susceptible to contracting mange and dying from that normally non-fatal ailment, NPS scientists report.

On July 6, biologists found P-65’s den of mountain lion kittens and tagged them“ P-88, P-89 and P-90, a female and two males. (Photo by Jeff Sikich, National Park Service)

On July 6, biologists found P-65’s den and tagged three mountain lion kittens – P-88, P-89 and P-90, a female and two males. (Photo by Jeff Sikich, National Park Service)

On July 6 2020, biologists found P-65’s den of mountain lion kittens and tagged tthem – P-88, P-89 and P-90, a female and two males. (Photo by Jeff Sikich, National Park Service)



In the past, scientists have successfully treated mountain lions suffering from mange by using a topical anti-parasitic medicine.

Scientists determined P-65 was infected with mange due to an infection caused by mites of the genus Notoedres. A severe case of notoedric mange causes hard, crusty skin, hair loss and open sores that can invite bacterial infection and extreme lethargy, said Winston Vickers, a veterinarian researcher at UC Davis who specializes in bobcats and mountain lions.

NPS researchers and other scientists say the presence of rat poison in P-65’s system prevented the lion from fighting off the disease, or it overworked her immune system to the point of failure.

NPS scientists first noticed the connection between rat poison and mange in bobcats in the early 2000s. The collared bobcat population in the Simi Hills, Thousand Oaks, Agoura Hills and Oak Park dropped by 50% between 2003 and 2006. Necropsies found that 92% of the dead bobcats analyzed tested positive for rodenticides.

Ten years ago, U.S. Geological Survey scientists collared two bobcats in the Whittier-Puente Hills. The healthy couple began to falter. First the female, WIN, died of severe mange and her partner, ZEK, contracted it a short time later. The scientists captured ZEK, treated him at an Orange County veterinarian office, and released him back into the wild where he thrived, the agency reported.

In the early 2000s, the connection to rodenticides was established in such over-the-counter products as d-CON, which contained the active ingredients brodifacoum, bromadiolone or difethialone. Scientists believe the poison also may have killed birds of prey such as owls and hawks that eat rodents that ingested poison, and that it weakened larger mammals as it intensified higher up the food chain, harming foxes, coyotes, bobcats and mountain lions.

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Josh Rosenau, conservation advocate with the Sacramento-based Mountain Lion Foundation, said mountain lions in the Santa Monica Mountains are hemmed in by roads and freeways and die in fatal collisions with vehicles. But the isolation also forces lions to eat smaller mammals that live closer to buildings and rat poison, especially when deer, a preferred mountain lion food, are not present.

“The options for foraging get limited. So they eat things not preferred, like rodents, rabbits and raccoons,” Rosenau said. “That restriction increases the risk.”

Vickers, who studies mountain lions in Riverside, Orange and San Diego counties, said there are far fewer cases of mange in the Los Angeles area population. He theorized that the Santa Monica Mountain area lions may have a genetic defect that makes them prone to mange.

He only remembered one mountain lion with a severe case of range in the southern and inland ranges, and it had to be put down. He says mange is very treatable.

In fact, the most famous mountain lion in Los Angeles, P-22, who roams the hills of Griffith Park and was on the cover of the December 2013 issue of National Geographic with a backdrop of the Hollywood Sign, was successfully treated for mange in 2014. Like P-65, tests revealed diphacinone and chlorophacinone in P-22’s blood.

In the NPS study in collaboration with UCLA, of 140 bobcats, coyotes and mountain lions evaluated, 88% tested positive for one or more anti-coagulant compounds. An anti-coagulant thins an animal’s blood and can lead to the animal bleeding to death internally, NPS scientists reported.

A wildlife overpass is being constructed over the 101 Freeway in Agoura Hills so animals can move from one area to the next safely. Ironically, P-65 was the second female puma to cross the 101 in NPS’s study history, when she traveled from the Liberty Canyon area where the overpass is being built into the Simi Hills. She actually darted across the roadway a second time, returning to the central Santa Monica Mountains.

She had three kittens in the summer of 2020, P-88, P-89 and P-90. The latter two were captured and received radio collars and both had mange, were treated and recovered. But P-89 and P-90 were killed on local roads: P-89 died on the 101 Freeway in Woodland Hills in July 2022 and P-90 died several weeks ago on Highway 33 in Ventura County, the NPS reported.

Related links

Rat poison found in mountain lion P-54 and her four unborn kittens after she was killed by a car
Mountain lion struck, killed by vehicle in Santa Monica Mountains
Bobcats face deadly diseases, weakened immune systems from exposure to household rat poison
ZEK the bobcat released back into the wild
Ground broken for $87 million wildlife bridge over 101 freeway to save mountain lions and other creatures

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