Rodenticides by definition are any agents that kill, repel or control rodents. Wikipedia defines rodenticides as “pest control chemicals intended to kill rodents”. Many rodenticides, in fact most used in the United States, include anticoagulants as the primary ingredient. Anticoagulants are usually classified as first generation or second generation.

Those classified as second generation have a much longer duraiton of action and include brodifacoum and bromadiolone among numerous others. Warfarin is the most common first generation anticoagulant, but resistance has developed in some rodent populations. Second generation anticoagulants have become the ingredients of choice in many rodenticides as they require less exposure and last longer in the body, making them more effective with less reported resistance.

Anticoagulant rodenticides are formulated as ready-to-use baits including impregnated powders, grains and seeds. Paste, block, gel and liquid preparations are also available and tend to be stronger. In some rodenticides, anticoagulants may be combined with other toxic chemicals. Accidental poisoning of household pets such as dogs and cats, as well as children, are common due to primary consumption. Although wildlife can be primarily exposed to rodenticides, secondary exposure by the consumption of dead or dying rodents previously exposed to rodenticides is the most significant type of exposure. Unfortunately, this type of toxin exposure is very difficult to quantify and evaluate as doses can be lethal but may also be cumulative, requiring repeated or prolonged exposure. Often, death occurs far from the original site of exposure. Most rodenticides take from one to five days to kill. Non-lethal exposure may not result in the immediate death of non-target species but can still alter the ability of the affected animal to thrive, reproduce and care for offspring. Secondary poisonings are more likely to occur from second generation anticoagulant-based baits.

Anticoagulants are absorbed from the digestive tract and act by inhibiting enzymes in the liver responsible for the production of vitamin K. Vitamin K is required to activate special proteins required in the process of blood clotting. The resulting reduction of vitamin K in the body results in fewer activated forms of important clotting factors and the body loses the ability to control even the most insignificant bleeding. The end result is the affected animals bleed to death internally. From the time of exposure to the time of death it may take 1-5 days, with duration of effects from secondary exposures lasting as long as 12-15 days or more. Clinical signs in affected animals may include persistent bleeding from the nose, gums, bowels and any wounds as well as excessive bruising. Pale mucous membranes, depression, lethargy, weakness, inappetence, anorexia, and anemia (low red blood cell count) are all frequent presenting signs for affected wildlife.

Cases of rodenticide toxicity involving anticoagulants are good examples of why rescued animals should be handled minimally to avoid injury (therefore bleeding) and not fed until a rehabilitator or veterinarian has identified the problem and started appropriate treatment, as there may be internal bleeding and a resulting condition of shock. Treatment of definite or suspected cases of anticoagulants in non-acute cases (meaning that the toxicity is greater than 2 hrs duration) usually consists of intramuscular injections and oral use of active vitamin K followed by supportive care for potential shock. Treatment, if initiated in time, can work quickly to normalize clotting; however, many second generation anti-coagulants such as commonly used brodifacoum persist in the organs even at non-lethal doses for up to the entire lifetime of the contaminated rodent. This means predators such as birds of prey, foxes, bobcats, etc. can acquire lethal doses by accumulation effect. They can become sick after eating enough rodents with even very low concentrations of the poison present in their bodies. This same persistence makes treatment very difficult, as the animals affected need to be treated for very long periods of time, something that is often difficult. The dangers of many second generation anticoagulant rodenticides due to bio-accumulation are only now being realized by many state and government agencies. Reaction is often slow and legally opposed by the manufacturers of the products in question. Although beyond the scope of this article, the author encourages the reader to investigate further specifics of the danger that second generation anticoagulants present to both avian and mammalian predators.

Choosing a method of rodent control is a decision most people do not take seriously enough, often reaching for weapons of mass destruction (second generation anticoagulants) rather than more appropriate measures such as the large number of effective and environmentally safe traps, reduction of available food and nesting sites of the rodents in question, and finally the importance of natural predators such as owls.

When poisons are used in rural areas or near city parks with native raptor populations, the use of poisons may initially be associated with a significant reduction in the rodent population; however, as soon as the poisons stop being used the rodent population returns. With the predators killed off by secondary exposure, the new rodent population is left without natural population control resulting in even larger numbers.

Please make the responsible decision not to use rodenticides, particularly the potent second generation products discussed here. These products may have their place but only in the most limited and isolated situations. For further information about the dangers of rodenticides and great information about encouraging natural predators, specifically birds of prey, please go online to sites such as and Help support the victims of wildlife poisoning in your area by supporting your local wildlife rehabilitators by visiting our website today.