We don't know what killed P-41, one of the few mountain lions left scratching out a living in the hills and urban mountains of Los Angeles. He was found dead in the Verdugo Mountains in October. But this week we learned that the 10-year-old big cat had rat poison in his system, including an especially toxic version that was outlawed for consumer use in 2014.
If rat poison wasn't what ultimately killed P-41, it very likely helped finish him off. And it wouldn't be the first time rat poison was implicated in the death of a local mountain lion. Two years ago, a 2-year-old female puma known as P-34 died from rat poison exposure, prompting wildlife officials to lament that the existing bans on consumer-grade rat poisons weren't working to stop the toxic substances from getting into the food chains and harming animals we don't want to get rid of: foxes, bobcats, owls and other birds of prey, not to mention Fluffy and Fido.
Both the state of California and the U.S. Environmental Protection Agency have restricted consumer sales of second-generation anti-coagulant rat poison because it is particularly dangerous to wildlife. The danger stems from the poison's latency: One dose is enough to kill a rat, but death doesn't come right away. So the rat continues to gobble up so much of the poison-laced food that when it finally keels over, it becomes an intensely toxic snack for the next animal up the food chain. Park officials say most mountain lions found dead in California had rat poison in their bodies, and studies have found other mammals and birds of prey are often exposed. The poison can kill them directly or weaken them so much that they are more likely to die from other causes.
Officials at the state's Department of Pesticide Regulation say it's still too early to judge the effectiveness of the 2014 ban. They suspect some consumers may still be using the banned poison, either drawing on stores stockpiled before the ban or getting fresh shipments online.
Use of second-generation rat poison is supposed to be restricted to professional pest exterminators and farms, and you won't find it for sale at "consumer" stores like Home Depot. But you don't have to be a professional to buy a 16-pound pail of Brodifacoum, a highly lethal second-generation anticoagulant, for $80 or so at a do-it-yourself pest control shopping site online.
Officials may ultimately find that the only way stop rat poison from getting into the wildlife food chain is to slap further restrictions on its sale. But the sad reality is that even if this particular class of poisons were banned outright, it would probably be replaced with another with its own unintended effects.
Indeed, that may already be happening. One popular and permissible consumer rat poison is a neurotoxin called Bromethalin (marketed by one company as "Bromethalin Bait Chunx" – yum!). It may be safer for wildlife, but it's worse for house pets that stumble across it and scarf it down; unlike second-generation rat poison, it works quickly, has no antidote and is difficult to detect. The American Society for the Prevention of Cruelty to Animals reported earlier this year that rodenticides are the most common source of pet poisoning in California and 24 other states, and most often Bromethalin is the culprit.
The only safe poison, of course, is no poison at all. This doesn't mean we have to let the rat population go unchecked; that poses its own, very real health threat. But there are nontoxic ways to control vermin infestations that are just as effective as environmentally destructive poison bait, albeit more time-consuming. They include being vigilant about yard maintenance, sealing up openings in buildings to keep rats from getting inside, and deploying tried-and-true snap traps. It certainly doesn't help to accidentally poison the very animals that prey on rats and help keep their numbers down.
It may be necessary to use poison in some circumstances. But even then it should be left to professionals with a full understanding of the dangers inherent in putting poison into the neighborhood food chain.