Anticoagulant Rodenticides are Wreaking Havoc with Wildlife

by Martha Rullman

March 30, 2025

A red tailed hawk found on the ground, thin, weak and bruised. A nesting bald eagle found disoriented and severely anemic, along with its mate found later in the same condition. A great horned owl that fell out of its nest to the ground, its two chicks in the nest sickened from the prey being fed to them by the parent….

These are just a a few examples of the kinds of wildlife casualties that are becoming more common in both urban and rural areas as the use of second generation anticoagulant rodenticides, known as SGARs, has increased in Massachusetts and thoughout the country. And while wildlife rehabilitators are spending more time and resources treating raptors and other wildlife poisoned by SGARs, those cases mentioned above represent only a small number of animals in the wild that are being sickened and killed by these poisons.

Raptors and other predators play a critical role in in the ecosystem, helping to keep it in balance by naturally controlling rodent populations. When hawks, owls, foxes and other predator species decline due to poisoning, rodent populations can surge, leading to increased human-wildlife conflicts and greater demand for rodent control, perpetuating a "cycle of poison.” Studies in Massachusetts and across the U.S. have shown widespread exposure of raptors and other predators to SGARs. Even when exposure does not lead to immediate death, sublethal doses from repeated exposure can weaken animals, affecting their health and reporoduction and making them more susceptible to disease, starvation, and vehicle collisions. In the last decade, there has been a steady increase in the number of birds of prey coming into Tufts Wildlife Clinic with rodenticides in their systems. Necropsies of dead hawks and owls frequently reveal internal bleeding and high concentrations of these poisons in their systems. The results of a recent study done there revelaed 100 percent of the red-tailed hawks tested positive for exposure to anticoagulant rodenticides. Another study of 46 predators admitted to Cape Ann Wildlife Rehabilitation Center between 2022 and 2024, including birds of prey as well as foxes and coyotes, found that all of them had SGAR poisoning.

SGARs are the primary type of rodent control used by licensed pest control companies today. Since the commercial sale of these chemicals was banned by the EPA in 2015 due to safety concerns, their use by the pest control industry continues to be permitted in every state except California, where a statewide bill was passed in 2020 banning their use with few exceptions. According to the Massachusetts Department of Agricultural Resources Pesticide Program, in 2022, around 95 percent of the rodent contol treatment used by pest control companies in the state was SGARs. Any discussion of this problem requires looking at the proliferation of the ubiquitous black boxes, sometimes disguised as gray rocks, placed outside along the sides of buildings and around stuctures such as dumpsters. These refillable bait boxes allow continuous and indisicrimate poisoning of target and non-target animals alike, either by primary poisoning from ingesting the bait directly, or through secondary poisoning, when a predator or scavenger consumes a mouse, rat or other animal that has been poisoned. SGARs work by preventing blood from clotting, leading to a slow and painful death from internal bleeding. Since these poisons work slowly and bioaccumulate, a rodent may feed at a bait station multiple times, and as it becomes weakened or dies, it’s an easy target for a prey animal or scavenger.  Poisoning ultimately leads to fatal hemorrhaging and organ failure, and a lethal dose typically occurs between four days to as long as two weeks after a rodent begins to feed on the bait. Hawks have even been observed perched nearby bait stations waiting for rodents to exit the boxes. In addition, since rodents store or “cache” food, non target species, including chipmunks, squirrels, rabbits, raccoons, groundhogs and opossums, are often poisoned when they find and ingest bait that has been carried out of the box. The pesticide industry’s aggressive promotion of long-term use of SGARs through the placement of bait boxes as a long-term solution for business and property owners dealing with rodent problems is not only killing off the natural predators of rodents, but it is also having a devastating impact on wildife because it has become pervasive and widespread in the wildlife food chain.

Martha Rullman has a background in natural resource management and education and a Masters degree in Environmental Studies. She is retired now but did conservation research and field work focusing on birds. She has been a resident of Northfield since 1990.  

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Massachusetts Audubon’s Rescue Raptors and Wildlife Campaign is a statewide initiative that supports volunteers in communities across the state to engage in outreach and education efforts to raise awareness about the harms of anticoagulant rodenticides, advocate for local and statewide legislation to restrict or prohibit their use, and encourage the use of safer and more humane rodent control alternatives. The Rescue Raptors Connecticut River Valley group is looking for volunteers to get involved in this coalition.  For more information about ways to get involved and to learn about what some other communities have done at the local level to reduce the use of rodenticides, go to the Mass Audubon's Rescue Raptors website below.

https://www.massaudubon.org/take-action/advocate/rescue-raptors