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Rodenticides can harm wildlife; please use carefully
Throughout California, the use of poison baits used to control rodents has injured and killed numerous wild animals and pets. This is because predatory and scavenging birds and mammals like owls, hawks, raccoons, foxes, skunks and coyotes that eat dead or dying rodents that have consumed these baits will also be poisoned.
Pets will also eat dead or dying rodents and unprotected bait. You can protect both pets and wildlife by reading – and following – the label directions of any rodent baits you purchase, and only purchasing those that are legal for the pest you are trying to control. Non-chemical means of rodent control, such as exclusion and santitation, should be used when possible to prevent rodenticide exposure to non-target wildlife and pets. Because of documented hazards to wildlife, pets, and children, the U.S. Environmental Protection Agency is in the process of canceling products that do not comply with safety requirements (see www.epa.gov/pesticides/mice-and-rats).
Protect your wild neighbors and pets from accidental poisoning. Use all pesticides very carefully and follow all label directions, or choose non-chemical pest control methods.
Rodenticide Baits: Frequently-Asked Questions
Q. How do rodent baits harm wildlife and pets?
A. It's possible for wildlife and pets to consume the poison directly. However, it's more common for some animals to receive a secondary exposure. A secondary exposure occurs when wildlife or pets consume dead or dying rodents that have eaten the rodent bait. Wildlife that can be affected by secondary poisoning include owls, hawks, eagles and mammals such as raccoons, foxes, bobcats, mountain lions and coyotes.
Q. How can I protect wildlife and pets, but still control rodent pests?
A. The most effective and safest ways to address rodent issues are through exclusion and sanitation. For example, seal off entrances to your home, remove debris from your yard, and make pet food inaccessible to rodents. Traps can also be effective in removing rodent pests. If you use rodent bait, it is important to follow label directions carefully. Rodent baits with the active ingredients brodifacoum, bromadiolone, difethialone, and difenacoum are very toxic and persistent and have been found widely in non-target wildlife. Baits containing chlorophacinone, diphacinone, warfarin, cholecalciferol and bromethalin are better choices; however, any rodent bait has the potential to harm non-target wildlife and must be used carefully and according to the label.
- Read product labels carefully before using any pesticide, and follow directions exactly.
- Check daily for dead rodents. Wearing gloves, collect the carcasses as soon as possible, place in plastic bags and dispose in garbage cans with tight lids that other animals can't open. Always wear protective gloves when handling any dead animal.
Q. What kind of rodenticide is legal to use for field rodents?
A. Diphacinone, chlorophacinone, and warfarin are first-generation anticoagulant rodenticides that can be used for control of field rodents.
Q. Why are chlorophacinone and diphacinone safer to use in open spaces?
A. Chlorophacinone and diphacinone are less toxic to mammals, and are eliminated more quickly from the bodies of animals that ingest them. These products generally require multiple feedings before killing rodent pests.
Q. What kind of rodenticides should I NOT use in the yard, away from buildings?
A. Over-the-counter rodenticides, such as d-Con®, that contain the active ingredients brodifacoum, bromadiolone, difenacoum or difethialone. These can only be legally used to control rats and house mice in and around structures. It is illegal to use these products in open areas such as pastures or fields. Products containing bromethalin and cholecalciferol may also not be used for field rodent control.
Q. Why is brodifacoum so dangerous for wildlife and pets?
A. Brodifacoum, bromodialone, difenacoum and difethialone are toxic to rodents in a single feeding. However, the rodent will not die until several days after feeding and may continue to ingest more poison. The poison is then available to a predator or scavenger that eats the rodent. If the exposed rodent does not die, the poison can persist in its body for several months.
Q. How do these rodent baits work?
A.. Brodifacoum, bromodialone, difenacoum and difethialone are second-generation anticoagulants. Warfarin, chlorophacinone, and diphacinone are first generation anticoagulant rodenticides. Both kinds of anticoagulant rodenticides work by disrupting blood clotting. Animals that ingest them die from internal hemorrhaging (bleeding) several days after ingesting the material. While the mechanism of all anticoagulants is similar, second-generation products (brodifacoum, bromadiolone, difenacoum and difethialone) are much more toxic and persistent and pose a much bigger threat to non-target wildlife. Cholecalciferol is an acute rodenticide which causes hypercalcemia. Bromethalin is an acute neural toxicant.
Q. How do you know rodent baits are poisoning wildlife?
A. Since 1994, CDFW's Wildlife Investigation Laboratory has confirmed at least 300 cases of wildlife poisoning from anticoagulant rodent baits. Brodifacoum was the poison most frequently detected. Animals harmed include coyote, gray fox, San Joaquin kit fox, raccoon, fox squirrel, bobcat, red fox, gray fox, mountain lion, black bear, Hermann's kangaroo rat, bald eagle, golden eagle, Canada goose, great-horned owl, barn owl, red-shouldered hawk, red-tailed hawk, Cooper's hawk, turkey vulture and wild turkey.
Since animals typically retreat to their dens, burrows or other hiding places in the final stages of anticoagulant poisoning, the number of non-target wildlife killed by these compounds is likely be much greater than we know. Field monitoring of wild populations of bobcats, mountain lions, coyotes, San Joaquin kit foxes, fishers, and raptors confirm widespread exposure to predatory and scavenging wildlife.
Q. Can I control rodent pests without using poison baits?
A. The most effective rodent control program uses exclusion techniques (such as sealing entrances to your home) and sanitation (removing rodent habitat such as ivy or wood piles); animal removal is used only when necessary. More information on controlling mice, rats, and field rodents is provided on the University of California Integrated Pest Management Website.
Q. I found a dead raccoon (or other small wild animal) in my yard. What should I do?
A. First, do NOT touch it bare-handed. Wildlife can carry diseases and parasites, so always wear protective clothing – especially gloves – before handling dead or dying animals of any kind. If you're in an urban or suburban area, you can call your city or county animal control office with detailed information about the animal's appearance and condition. Even if they don't have the staff to come retrieve it, they may like to know about it, as the one you found may not be the only one.
Q. If I think my pet has been poisoned, what should I do?
A. If your pet is having seizures, is unconscious or losing consciousness, or is having difficulty breathing, phone ahead and take your pet immediately to your local veterinarian or emergency veterinary clinic. In addition, if you see your pet consuming rodenticides, call your veterinarian immediately – do not wait for symptoms. If you are aware of any rodenticide that your pet has had access to, bring this information with you as it will help the veterinarian effectively treat your pet.
Rodent baits are often used to control voles. Their populations tend to be cyclical and once established, vole colonies are not easy to control. Control measures are much more effective if applied early in the cycle.
One of the most effective ways to discourage voles from moving in is to simply mow grasses down to no more than two inches or disk around sites that need to be protected. Either action will reduce or eliminate their preferred habitat. Often, if you don't control the vole population, there may be little you can do about it. The secret is to protect sensitive sites – such as gardens – by mowing or disking the area before the population gets too high.
If you must use a rodent bait to control voles, only use those baits intended for field rodents. Their labels will identify chlorophacinone or diphacinone as the active ingredient. Zinc phosphide can also be used for voles and is less likely to cause secondary exposure. All of these materials are restricted use, which means they can only be purchased by a certified applicator and used by or under the supervision of a certified applicator. Baits should only be used in small treatment areas and the areas should be checked daily for dead rodents. Prebaiting with non-toxic bait is a good way to ensure that only the target pests are likely to consume the toxic bait.
With very high vole populations, rodent baits may ultimately have little effect. The best approach is to protect sensitive sites – such as gardens – by mowing or disking the area before the population gets too high. The utilization of aluminum flashing as fencing can work to keep voles out of certain areas. The flashing should be buried a minimum of 10 inches below ground. It works best if an additional 6 inches of flashing was bent at a 90 degree angle away from the area where you want to keep voles out. This “lip” will decrease the likelihood that a vole will be able to dig around the structure. You would need to have an additional 8-12 inches sticking up above ground to prevent dispersal in this manner. These barriers are also far more effective if you have 1+ feet of bare ground around the base of the fence to keep voles from hanging around the fence, which would increase the chance that they find a way to dig around it.