Rat poison wreaks havoc across the animal kingdom, harming and killing everyone from mountain lions and bobcats to hawks and pet cats. 

The mountain lion known as P-47 had survived fires, freeways and hostile ranchers. But in March, the 3-year-old big cat—tracked by California biologists since his kitten days—succumbed to a more hidden hazard: an insidious form of food poisoning.

Six anticoagulant compounds—chemicals used to kill rodents—were found in P-47’s liver. He was also bleeding internally. He didn’t have to consume rat bait directly to become ill. As apex predators, mountain lions can inadvertently absorb a toxic soup through their natural diets, eating poisoned rodents as well as other predators who’ve fed on them. Ninety percent of those tested in the Santa Monica Mountains region have been exposed to rodenticides, as have most bobcats and coyotes.

“The number of animals who get either compromised or die from these poisons is enormous,” says John Griffin, director of urban wildlife programs for the Humane Society of the United States. “We’re awash in rodenticides.”

Anticoagulants prevent blood clotting and can lead to hemorrhaging. Wildlife specialists know the signs well. When veterinarian Antonia Gardner at the HSUS-affiliated South Florida Wildlife Center treated a lethargic juvenile barn owl with no visible illness or injury, “he started oozing from the places where we were giving fluids,” she recalls, noting that the owl was likely fed poisoned rodents by his parents. “And he was developing bruising because his capillaries were not clotting.”

Even animals not killed directly suffer; researchers have linked the compounds to weakened immunity, recently confirming connections to mange in bobcats. Globally, anticoagulants are found in a wide range of animals, from European fish to Algerian hedgehogs to South African caracals. Another type of rodenticide, a neurotoxin, is devastating San Francisco’s wild parrots. One study even placed rodenticides above climate change in the list of threats to California’s endangered San Joaquin kit fox. “These poisons have made their way completely throughout the food web,” says Lisa Owens Viani of Raptors Are the Solution, an advocacy group working to end rodenticide use. “We feel like it’s our modern-day DDT because it’s so widespread.”

Now lobbying for greater restrictions across California, Viani started RATS after neighbors discovered dead Cooper’s hawks, including one fledgling found in a pool of blood. Raptor families consume hundreds to thousands of rodents annually, but “we are poisoning the very solution to the problem,” says Viani. Ventura County officials recently confirmed the value of natural predation, finding that installing raptor perches near levees resulted in fewer ground squirrel burrows than in areas treated with rodenticides.

Though the Environmental Protection Agency banned over-the-counter sales of the most acutely lethal, single-dose anticoagulant rodenticides in 2015, pest control operators still use them extensively. Off-the-shelf anticoagulants, which kill rodents through multiple feedings, wreak havoc, too. Rodents don’t die instantly from either type of bait and instead become easy prey; researchers in Colorado observed hawks preferentially preying upon prairie dogs made lethargic by rodenticides, and a San Francisco photographer watched a hawk picking off rats exiting a bait box outside a grocery store. Despite manufacturers’ claims to the contrary, bait box security is also a problem: Gardner has treated an opossum found in one, and Viani receives many reports of dogs breaking into boxes. Cat owners also report deaths-by-rodenticide after their cats eat poisoned prey. “I have horrific photos that people send me of the consequences,” says Viani. “These are definitely not safe for pets either, and I think a lot of people are finding out the hard way.”

The desire for out-of-sight, out-of-mind solutions causes unfathomable pain for millions of rats, too. People use rodenticides routinely, says Griffin, but “there should be a higher threshold for justifying that kind of control.” Unseen ripple effects are rarely considered; even bumblebees can be negatively affected by the use of rodenticides, as old rodent burrows are some of their favorite nesting sites.

Humane prevention is key; sealing structural holes, securing food and garbage, and removing bird feeders can reduce attractants. “Is it really worth feeding the birds,” asks Viani, “if you’re going to have a rat problem and then you’re going to put out poison, which in turn is going to kill other birds like hawks and owls?”

While homeowners work on permanent prevention, live traps can help transport rodents outside. Some cities and property owners are experimenting with fertility control bait—and results are so promising that even the pest control industry is promoting it as an effective, humane solution. “This kind of approach,” says Griffin, “is the future.”

For more information about humane exclusion, visit humanesociety.org/wildrats. Find news, resources and advocacy materials at raptorsarethesolution.org.

Postscript: Should you install a barn owl box?

Barn owl boxes are a promising humane alternative to rodenticides, drawing hard-working birds of prey to your land. But it’s important to remember the welfare needs of the owls when implementing such solutions. While adding barn owl boxes can be a positive step for vineyards, sometimes the boxes are placed out in the open with no shade. “So there’s nowhere for the owls to fledge, and there’s no protection from the sun,” says Christine Barton, director of operations at the HSUS-affiliated Fund for Animals Wildlife Center in Ramona, Calif. “It’s a box right out in the middle of a field.” When they start overheating, some owlets jump out of the box. Place the box under a tree or in a shady area instead, Barton recommends, or build an awning to keep owls protected.

(Featured image of red-shouldered hawk by Will Heinz)