Protecting Raptors from Rodenticides
Raptors and owls primarily feed on gophers, voles, and mice in Utah. A lethargic and meandering rodent that has fed on anticoagulant rodenticide bait is a prime target for birds of prey. Unfortunately, the bait on which the prey fed often kills the predator.
Second-generation anticoagulant rodenticides are non-selective, acutely toxic, and persistent. But they are also slow acting (3-7 days). Rodents can continue ingesting the bait beyond a lethal dose, and when death or near death occurs, they may contain 20-40 lethal doses of the active ingredient.
Raptors and wildlife that are exposed to anticoagulant rodenticides through feeding on poisoned prey are killed in the same manner as the target pest. The chemical prevents the enzyme that allows for synthesis of Vitamin K. Vitamin K is essential for blood clotting, and without it, death by uncontrolled internal bleeding occurs.
Both California and New York veterinarians have surveyed for anticoagulant ingredients in the blood and organs of dead raptors and other wildlife. Of the species tested, anticoagulants were found in 79% of fishers, 78% of mountain lions, 70 to 81% of owls, and 49 to 92% of raptors.
Due to the high number of poisonings reported each year– including to humans and pets–as well as the documented misuse of rodenticides by homeowners (improper dosage and placement), EPA has cracked down on residential use of second-generation anticoagulant ingredients. In 2011, they cancelled sales of loose bait and pellets of brodifacoum, bromadiolone, difenacoum, and flocoumafen, to homeowners. (d-Con products that contain brodifacoum are still available until administrative hearings of EPA against the manufacturer, Reckitt Benckiser LLC, which began in February 2013, are complete.) The remaining rodenticide baits containing the above active ingredients are still available in bulk quantities or in preloaded, tamper-proof bait stations.
Predators, scavengers, and pets are no less poisoned if they eat rodents that consumed bait from bait stations or loose pellets. Even when baits are used indoors, poisoned rodents can move outdoors where they can be fed upon. Poisoned rodents are at greater risk of being captured as prey than healthy animals. Rodents that ingest anticoagulant baits are weakened but still active for up to 7 days, facilitating the ability of predators to capture them.
Gophers and voles cause extensive agricultural losses and are nuisance pests. But they should be managed so that non-target poisonings are avoided. Where possible, single- and multiple-entrance snap traps or other humane devices should be used before rodenticides. If a rodenticide must be used, these active ingredients are somewhat safer for raptors: bromethalin, vitamin D3, chlorophacinone, warfarin, or warfarin sodium salt. Baits should always be in protective boxes, and never used during nesting season, when adult raptors could potentially feed poisoned rodents to their young and to each other.
-Marion Murray, IPM Project Leader
Erickson, W. and D. Urban. 2004. Potential risks of nine rodenticides to birds and mammals. Office of Prevention, Pesticides, and Toxic Substances. EPA. Washington D.C., 203 pp.
Rattner, B.A., et al. 2011. Acute toxicity, histopathology, and coagulapathy in American kestrels following administration of the rodenticide diphacinone. Environmental Toxicology and Chemistry. 30: 1213–1222. doi: 10.1002/etc.490
Albert, C. A., et. al., 2010. Anticoagulant rodenticides in three owl species from western Canada, 1988–2003. Archives of Environmental Contamination and Toxicology. 58:451–459.