In June the EPA announced that it will ban the sale of four particularly potent rodent poisons in retail stores because they鈥檝e proven harmful to people, pets, and wildlife. Professional exterminators, farmers, and government agencies will still be able to use the rodenticides, which some 15,000 children a year are exposed to, poison control data shows.
The new regulations could help prevent 鈥渙ff-target鈥 deaths while still allowing wildlife managers to employ the poisons as highly effective conservation tools. To safeguard species like great horned owls, red-tailed hawks, bobcats, and kit foxes, farmers must isolate the rodenticides in bait stations. Federal wildlife managers can continue using the poisons only for conservation efforts, such as protecting seabird nesting sites from invasive rodents.
鈥淚 think we have a broad contamination of the food chain,鈥 says Pierre Mineau, a pesticide ecotoxicologist at Environment Canada鈥檚 National Wildlife Research Centre and a leading expert in the field. In a study that examined 270 birds of prey, Mineau and his colleagues found that as many as 11 percent of great horned owls are at risk of being indirectly killed by these rodenticides. 鈥淵es, they work like gangbusters,鈥 says Mineau, 鈥渂ut do we really need to use that much of a powerful tool?鈥 The chemicals鈥攂rodifacoum, bromadiolone, difethialone, and difenacoum, which are found in products like D-Con鈥攁re second-generation anticoagulants that kill by causing fatal hemorrhaging. They are far more toxic than older poisons.
Ironically, for this reason, they鈥檝e played a role in some of the most dramatic conservation successes in recent history, says Greg Butcher, 约炮视频鈥檚 director of bird conservation. On New Zealand鈥檚 Campbell Island, California鈥檚 Anacapa Island, and more than 100 other islands worldwide, wildlife managers have resorted to the poisons to eliminate rats.
The U.S. Fish and Wildlife Service is considering using the rodenticides on California鈥檚 mice-infested Farallon Islands, nesting grounds for more than half of the world鈥檚 roughly 7,500 breeding ashy storm-petrels. The California Department of Fish and Game lists the bird as a species of special concern because its limited range makes it susceptible to oil spills and predation by rodents, cats, and other animals. 鈥淲e want to keep species off the endangered list,鈥 says Gerry McChesney, manager of the Farallon National Wildlife Refuge, adding that removing mice from the Farallon Islands will help do just that.
Burrowing owls that happen upon the islands during migration linger there because of the mice, likely introduced by sailors in the 1800s. The owls devour the rodents until their numbers naturally decline each winter, and then switch to embattled seabirds like the petrels. Wildlife managers have tried relocating some of the birds, but it鈥檚 very labor intensive and hasn鈥檛 solved the problem.
Now they鈥檙e planning a mouse eradication project, and rodenticides will be an option in the environmental impact statement due this fall. 鈥淚t鈥檚 really important to have rodenticide available for bird conservation,鈥 says Butcher. 鈥淕etting rid of rodents on the Farallon Islands is probably the number one thing we can do to help that species. You can trap rodents until the cows come home without ever really getting rid of them.鈥
Any rodenticides will be used with caution, says McChesney. For his part, Mineau hopes his findings will influence regulators, but also supports use of the chemicals for conservation: 鈥淚t鈥檚 one of those situations where you say, I鈥檓 going to accept some impact for the greater good.鈥
Correction: an earlier version incorrectly identified barn owls as a significant threat to ashy storm-petrels on the Farrallon Islands. It should have been burrowing owls.