Products Marketed to Kill Rodents are Instead Threatening the Lives of the Wildlife That Eat Them
Updated: Mar 26
Many people consider rodents to be pests- and often turn to an array of products, known as anticoagulant rodenticides, which are marketed to lethally “solve” the issue with poisoned bait. But researchers have been collecting evidence for years showing that it’s not just nuisance rats that can end up dead.
Some of the most recent studies, conducted in California, found that everything from Pacific fishers to bobcats to northern spotted owls often become victims of rodenticides. The list of potentially affected wildlife is long — basically anything that preys on a rodent could be at risk, because the poisons are so toxic they travel up the food chain, and in some cases, can remain in an animal’s body for years. It can even leapfrog in utero from one generation to the next.
“If you have a very poisoned rat, you’re going to have a very poisoned hawk,” says Kelle Kacmarcik, director of wildlife solutions and advocacy at WildCare, a wildlife rehabilitation center in Marin County, California. And that’s a huge problem.
A Widespread Problem
Anticoagulant rodenticides are sold under dozens of brand names with a number of different active ingredients. They work by affecting the animal’s processing of vitamin K, which inhibits clotting and coagulation, ultimately leading to uncontrolled internal bleeding. One of the most common first-generation anticoagulant rodenticides uses the blood thinner called warfarin as its active ingredient, but rats appear to have developed a resistance to it.
Manufacturers responded by developing a new line of more toxic products, using active ingredients like brodifacoum or bromadiolone, which have no medicinal uses. These second-generation rodenticides pack a bigger punch in a small amount and are designed to deliver a lethal dose to a rodent with just one feeding. They also have longer half-lives, which means the poison can stay in the animal’s liver for years, compared to just days or months with the first-generation poisons.
Both of these factors contribute to an increased possibility of nontarget wildlife eating poisons intended for rodents. Second-generation rodenticides don’t kill animals right away. It can still take days, and in that time a sick animal often consumes more of the poison and exhibits signs of illness, making it an easier target for predators.
“No matter how large or small, you’re looking at a toxic poison in the systems of these animals,” says Alison Hermance, director of communications of WildCare. And anticoagulants mean that even a small scrape can cause an animal to bleed out, turning an otherwise minor injury into something fatal.
Researchers have found animals in California with up to five different kinds of rodenticides in their systems at one time. Gabriel says that understanding all the ways sublethal doses of poison affect animals, including the build-up of multiple kinds of poisons, is “a new field of research that needs to be tackled extensively.”
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