Two Mountain Lions Dead of Rodenticide Poison

The death of P-30, a healthy six-year-old male, was caused by anticoagulant rodenticide poisoning. Photo and graphic courtesy NPS

Two mountain lions have been found dead in the Santa Monica Mountains recently and the cause of death for one of them, a healthy six-year-old male known as P-30, was anticoagulant rodenticide poisoning, say National Park Service biologists. The other cat found was P-53.

On September 9, biologists hiked into Topanga State Park to look for P-30 after his radio collar sent out a mortality signal. He was found dead with no obvious signs of injury or trauma. His carcass was collected and a necropsy by the California Animal Health & Food Safety (CAHFS) Laboratory field office in San Bernardino revealed that he bled to death internally. The report documented that he had severe hemorrhaging in his brain and abdominal cavity. Approximately five liters of unclotted blood was found in his abdomen.

Testing identified five different anticoagulant rodenticides, including a high concentration of bromadiolone (2100 parts per billion, ppb). Other compounds found included: brodifacoum, chlorophacinone, difethialone, and diphacinone.

Park officials say this is the fifth mountain lion in the long-term study of the species to die in this manner and that anticoagulant rodenticides, although intended to control rodents, can end up negatively impacting a wide range of wildlife—from the bottom of the food chain to the top.

Since 2002, National Park Service researchers have documented the presence of anticoagulant rodenticide compounds in 23 out of 24 local mountain lions that they have tested, including in a three-month-old kitten.

“Just about every mountain lion we’ve tested throughout our study has had exposure to these  poisons, generally multiple compounds and often at high levels,” said Seth Riley, an ecologist and the wildlife branch chief for Santa Monica Mountains National Recreation Area (SMMNRA). “A wide range of predators can be exposed to these toxicants—everything from hawks and owls to bobcats, coyotes, foxes, and mountain lions. Even if they don’t die directly from the anticoagulant effects, our research has shown that bobcats, for example, are suffering significant immune system impacts.”

Testing of P-64, who died a few weeks after the Woolsey Fire, also revealed six different anticoagulant compounds in his liver, as did P-47, who died from poisoning in April of this year. Mountain lions are likely exposed through secondary or tertiary poisoning, meaning that they consume an animal that ate the bait, such as a ground squirrel, or an animal that ate an animal that consumed the bait, such as a coyote. See infographic on how rodenticide can work its way up the food chain.

These recent mountain lion deaths, along with two other ones over the summer—P-38 and P-61—serve to highlight the challenges our local mountain lions face in the Santa Monica Mountains and surrounding region.

In terms of human mortality causes, vehicle strikes are the most common, followed by anticoagulant poisoning. Intraspecific conflict (lions killing other lions) has also been an important cause of mortality. This conflict is a natural cause of death but it is potentially more common because of the isolation caused by freeways and development. Biologists call this “frustrated dispersal.” P-61 was killed while trying to cross the 405 Freeway right after (or during) an intraspecific conflict, and P-38 was illegally shot in the head. 

P-30 was re-captured in February 2018 and given a new GPS collar. He is one of the more notable mountain lions of the study because he was the first male lion kitten to have been marked at the den and then to have survived long enough in the Santa Monicas to reach adulthood and establish a home range.

CAHFS did not find a cause of death for P-53, a four-year-old, female mountain lion. Her carcass was too decomposed by the time biologists reached her on August 15 in Malibu. However, testing did identify four different compounds of anticoagulant rodenticide in P-53’s liver: brodifacoum, bromadiolone, difethialone, and diphacinone, again including very high levels of bromadiolone (2000 ppb).

Previous remote camera photos had indicated that P-53 likely had mange, a condition caused by microscopic parasitic mites that burrow deep into the skin and cause severe itching, hair loss, and skin lesions. NPS consulted with veterinarians and disease experts with the California Department of Fish and Wildlife. When P-53 was recaptured in February of this year, upon confirming her mangy appearance, biologists treated her with selamectin, a topical treatment for ectoparasitic diseases such as mange, fleas and ticks.

Three months later, researchers captured remote video footage of the big cat that showed she had recovered from the mange. Although mange is generally rare in wild cats, it has been widespread in bobcats in the Santa Monica Mountains area since an outbreak that started in 2002 caused extensive mortality and a significant population decline. 

In bobcats, severe, fatal mange disease is highly correlated with the degree of exposure to anticoagulant rodenticides, and long-term, intensive studies by UCLA and NPS found widespread immune system impacts and altered gene expression in exposed animals. The same level of investigation has not been possible to date with mountain lions, but all five mountain lions in the NPS study that have become sick with mange, including the Griffith Park mountain lion known as P-22, have also been exposed to these toxicants. 

Since 2002, the National Park Service has been studying mountain lions in and around the Santa Monica Mountains to determine how they survive in an increasingly fragmented and urbanized environment. 

The California Department of Fish and Wildlife is responsible for overseeing the management and conservation of mountain lions in the state.


Santa Monica Mountains National Recreation Area (SMMNRA) is the largest urban national park in the country, encompassing more than 150,000 acres of mountains and coastline in Ventura and Los Angeles counties. A unit of the National Park Service, it comprises a seamless network of local, state, and federal parks interwoven with private lands and communities. As one of only five Mediterranean ecosystems in the world, SMMNRA preserves the rich biological diversity of more than 450 animal species and 26 distinct plant communities. For more information, visit


The chain of poison that led to the death of P-30 and P-53.


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