Second generation ultra-potent rodenticides pose danger for people, pets and wildlife

Poisons used to kill rodents have safer alternatives

By Ted Williams, Audubon

Published: January-February 2013

Clinical assistant professor Maureen Murray of the Tufts Cummings School of Veterinary Medicine in central Massachusetts was doing a good job of keeping her emotions under wraps as she clicked through photos of her recent necropsies. But I was watching her eyes as well as her computer screen, and they revealed anguish. Like her colleagues here and at similar clinics around the country, Murray is a wildlife advocate as well as a scientist.

Each image was, in her word and my perception, “sadder” than the last. There was the great horned owl with a hematoma running the length of its left wing; the red-tailed hawk’s body cavity glistening with unclotted blood; sundry raptors with pools of blood under dissected skin; the redtail with a hematoma that had ballooned its left eye to 10 times normal size; and, “saddest of all,” the redtail with an egg. The well-developed blood vessels in her oviducts had ruptured, and she had slowly bled to death from the inside.

All these birds were victims of “second-generation anticoagulant rodenticides” used by exterminators, farmers, and homeowners. They’re found in such brand names as d-Con, Hot Shot, Generation, Talon, and Havoc, and they sell briskly because of our consuming hatred of rats and mice. The most pestiferous species are alien to the New World and therefore displace native wildlife; they contaminate our food and spread disease. We also hate them for their beady eyes, their naked tails, and their vile depictions in literature, from Aesop to E.B. White. So the general attitude among the public is “if a little poison’s good, a lot’s better.” But even a little second-generation rodenticide kills nontarget wildlife.

Both first- and second-generation rodenticides prevent blood from clotting by inhibiting vitamin K, though the second-generation products build to higher concentrations in rodents and are therefore more lethal to anything that eats them. The second generation was developed by Imperial Chemical Industries of London at the request of the World Health Organization, because rats appeared to be developing tolerance to warfarin, a first-generation rodenticide.

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