Rodents are a group of mammals defined by one key feature: one pair of continuously growing front teeth in both the upper and lower jaws. We have a lot of rodent species in Maine, including mice, rats, squirrels, beavers, porcupines, and more.
Rodents are a fascinating and diverse family, but they’re not always the most popular animals. Many people view rodents, especially rats and mice, as pests, and sometimes use chemicals called rodenticides to control them.
However, the impacts of rodenticides are felt far beyond their intended targets. Animals like dogs or raccoons may consume rodenticides that have been left outside as bait. Other animals may accidentally ingest rodenticide when they eat poisoned prey. Many creatures may be affected by this secondary ingestion, including predators like owls, hawks, foxes, coyotes, and pet cats; and scavengers like ravens and crows, eagles, vultures, opossums, and more.
Wildlife is at risk, but states and the federal government are beginning to take action. Federally, U.S. Environmental Protection Agency has restricted the use of certain rodenticides, though some dangerous chemicals are still available online to be purchased by anyone. In 2020, California enacted the California Ecosystems Protection Act that placed a moratorium on certain uses of Second-generation anticoagulant rodenticides (SGARs). And recently, California’s Poison-Free Wildlife Act expands the moratorium to many FGARs. In addition to California, Connecticut, South Carolina, and Vermont have all restricted the sale and use of SGARs.
Legislation to advance restrictions on these chemicals was passed in the Maine Legislature last year. The bill, LD 356, tasked the Board of Pesticides Control (BPC) with delivering a report in early 2026 with an update on recommended prohibitions. Maine Audubon is calling on the state BPC to ban the sale and use of SGARs in Maine. Banning second-generation anticoagulants would eliminate the most deadly and most persistent rodenticides in use.
If you agree, read more information below and sign our petition here.
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Rodenticides can be categorized into two chemical classes: anticoagulants (ARs) and non-anticoagulants. Anticoagulant rodenticides include ingredients that halt the blood clotting process of a rodent, leading to fatal internal bleeding. Fatal hemorrhaging is usually triggered by an external injury or even normal activity and can lead to days of suffering before the animal dies. First-generation anticoagulants (FGARs) were developed in the 1940s and require multiple feedings to be effective. Common FGARs include warfarin, chlorophacinone, and diphacinone. These three ARs may differ slightly in their chemistry but have the same effects on organisms. What’s more, diphacinone is the main ingredient in many consumer-facing products such as Tomcat Rat and Mouse Bait. By the 1970s, rodents began developing resistance to FGARs and new rodenticides called second-generation anticoagulant rodenticides (SGARs) were developed. Both ARs bioaccumulate in the fatty tissue of animals which increases the risk of secondary exposure to non-target species. SGARs are drastically more potent than FGARs and take longer to break down and therefore persist in animal tissue longer. This means that poisoned rodents, dead or dying, that are eaten by other animals are toxic for a longer period of time. Common SGAR ingredients include brodifacoum, bromadiolone, difenacoum, and difethialone.
In addition to anticoagulants, there are many non-anticoagulants in use as well. One example is bromethalin. Bromethalin is a neurotoxin found in popular consumer products such as Tomcat and is often advertised as an agent that can kill anticoagulant resistant rodents. Bromethalin inhibits cells from properly regulating fluid balance which causes the central nervous system to accumulate fluid leading to pressure on the brain and eventually death. Unlike ARs, many non-anticoagulants break down relatively quickly and the risk of secondary exposure is not as high. However, new research demonstrates that bromethalin can bioaccumulate as well.
Unfortunately, wildlife and companion animals like cats and dogs are impacted by the use of highly toxic rodenticides. Rodenticides have been found to occur extensively in wildlife. This prevalence is due to the ability of rodenticides, specifically anticoagulants, to bioaccumulate in fatty tissues for extended periods of time. Some FGARs have half-lives that range from 2-26 days, while SGARs can have half-lives up to 350 days. Because of these extended half-lives, anticoagulants can persist for long periods of time increasing the risk of secondary and even tertiary exposure.
Primary exposure occurs when nontarget species—including animals such as raccoons to even dogs—directly consume rodenticides Secondary exposure occurs when a predator consumes poisoned prey. And tertiary exposure occurs when an animal consumes another animal that consumed a poisoned animal. Nontarget species exposure is exacerbated by the fact that poisoned prey are weakened and disoriented, making them easy targets for predator species. It is also important to note that some exposures may be sub-lethal meaning that a non-target animal can experience the effects of poisoning for an extended amount of time without succumbing to the poison—increasing the amount of time the animal suffers and further increasing the likelihood of secondary and tertiary exposure.
Due to these exposure pathways, ARs are prevalent in most animals tested for rodenticides. In Massachusetts, 100% of Great Horned Owls tested for ARs between 2006 and 2016 were positive for at least one type of AR. Another study focusing on fishers in Vermont and New Hampshire found that 98% of the 45 fishers tested were positive for at least one AR. And this exposure is often deadly. While wildlife poisoning deaths can be hard to quantify, rehabilitation centers have demonstrated the impact of these rodenticides. A recent article highlighted that 86 of 148 birds of prey brought into the Rhode Island based Congress of Birds rehabilitation center died or were euthanized due to rodenticide poisoning during 2024. Another article explained that the Massachusetts based New England Wildlife Center sees between 100 and 200 secondary rodenticide poisoning cases each year.
To better safeguard Maine’s environmental health, it is essential that the state restricts these dangerous chemicals. As an important and urgent first step, Maine Audubon believes that the Board of Pesticides Control (BPC) should ban the sale and use of SGARs in Maine. Although this would not be a complete ban on all rodenticides, banning second-generation anticoagulants would eliminate the most deadly and most persistent rodenticides in use.
