I inspected the tiny creature closely. It must have died recently, its brown and white furred body still soft and supple. Was it an outdoor cat that killed it? It certainly could have been. Free roaming cats have left quite a number of birds and small mammals for me over the years. But there didn’t appear to be any signs of trauma; no puncture wound and no blood. Hmmm. I dismissed the thought that this animal was poisoned—surely my immediate neighbors know that rat bait is a wretched solution? I left the mouse where it was, figuring it could be food for some other critter. Unfortunately, this was a mistake.
Today’s most widely used rat poisons are second-generation anticoagulants: highly toxic not only to the rodents that directly consume the bait but also to the non-target animals that eat the contaminated rodents.
Although the EPA has prohibited the sale of products containing brodifacoum, bromadiolone, difenacoum and difethialone directly to consumers, pest control companies and farmers are still allowed to use these second-gen anticoagulant rodenticides.
Like the first-generation of anticoagulants that preceded them, the “superwarfarins” prevent blood from clotting, induce internal bleeding and inflict a prolonged, painful death. However the newer poisons are many times more potent. “Second-generation anticoagulants,” the EPA explains, “are more likely than first-generation anticoagulants to be able to kill after a single night’s feeding. These compounds kill over a similar course of time but tend to remain in animal tissues longer than do first-generation ones.” This means that by the time the rodents die—five to seven days after consuming the bait—they can have up to 30-40 times the lethal dose in their bodies. Meanwhile, they stumble about and are easy prey for predators and pets.
Collateral poisonings of carnivores and omnivores alike are widespread wherever bait boxes are being deployed. The affected wildlife are more likely to get hit by moving vehicles, crash into structures or be killed by other animals. These non-target animals are also more susceptible to disease and vermin. In California, most coyotes, bobcats and cougars that die from mange—a skin disease caused by parasitic mites—also test positive for rodenticide exposure.
The Centers For Disease Control receive about 15,000 calls per year from parents whose children have eaten rodenticides.
If you are considering a trap and release, please read Nancy Lawson’s article Stranger in a Strange Land before you do.
The Humane Society—What to do About Wild Mice
Scientific American—Blood Thinning Rat Poison is Killing Birds Too
Safe Rodent Control—Risks for Wildlife
Environmental Protection Agency—Controlling Rodents and Regulating Rodenticides