The Hidden Costs of Rodent Poison
- vermontmuseum
- Feb 24
- 5 min read
By Martha Rullman
A red tailed hawk found on the ground, thin, weak, and bruised. A nesting bald eagle discovered near a park, 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 poisoned prey being fed to them by their parent….
These are just a a few examples of the kinds of wildlife casualties that are becoming increasingly common in both urban and rural areas, as the use of second generation anticoagulant rodenticides, known as SGARs, has increased in Vermont and throughout the northeast and the country. While wildlife rehabilitators are spending more time and resources treating raptors and other wildlife poisoned by SGARs, animals that are found and brought in to wildlife rehabilitators represent only a tiny fraction of animals in the wild that are being sickened and killed by these poisons.
Raptors and other predators play a critical role in the ecosystem, helping to keep things 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.” 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 several studies done there revealed that 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 been poisoned by anticoagulant rodenticides.
A species that has been gaining more attention as a result of increased in secondary poisoning from rodenticides in wildlife is fishers. The alarming decline in fisher populations in the northeast has been documented by biologists from the Vermont Fish and Wildlife Department. After their reintroduction in the 1950s, fisher populations in the Northeast gradually recovered from over trapping and habitat loss, but they have been steadily declining in the last two decades. In a study conducted in five Northeastern states, exposure rates to multiple anticoagulant rodenticides were the highest in Vermont, with 98% of fishers testing positive for multiple rodenticide compounds. Given the elusive and solitary nature of these animals, widespread population decline from chronic rodenticide exposure is indicative of how ubiquitous these poisons are in the environment.
Anticoagulant rodenticides indiscriminately kill animals by primary poisoning, when an animal is poisoned by ingesting the bait directly, or by secondary poisoning, when a poisoned animal is eaten by predator or scavenger. These poisons work by preventing blood from clotting, leading to a slow and painful death from internal bleeding. Since these chemicals work slowly and bioaccumulate, a rodent may feed at a bait station multiple times, and as it becomes weakened, 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. But sublethal poisoning from chronic rodenticide exposure is common in mid-ranking predators such as foxes, coyotes, and bobcats. As these animals immune systems are weakened, they become more vulnerable to disease such as mange and starvation, vehicle strikes, and low reproductive success.
The poisoned bait is typically placed in bait boxes, but non-target species are also often victims of primary poisoning when they find and ingest bait that is found outside of the box. Rodents store their food as a survival mechanism, and the bait can easily be removed and cached in the environment, where other animals like birds, rabbits, squirrels, chipmunks, raccoons and opossums can find and ingest it. Invertebrates such as snails are also attracted to the bait and can easily get into bait boxes, and they can then be consumed by birds and other non target species. The bait box becomes a reliable source of food and shelter, and hawks have even been observed perched near bait boxes waiting for rodents to exit.
Since the commercial sale of SGARs was banned by the EPA in 2015 due to safety concerns, their use by licensed pest control applicators continues to be permitted in every state except California, where a statewide bill was passed in 2020 banning their use with certain exceptions. In spite of the federal ban on retail sales, they have become the primary means of rodent control in the pest control industry. According to the Massachusetts Department of Agricultural Resources Pesticide Program, in 2022, around 95 percent of the rodent control treatment used by pest control companies was anticoagulant rodenticides.
An understanding of the problem requires looking at the widescale and long term placement of bait box stations along buildings and around structures. Pest control companies restock these ubiquitous bait boxes on a monthly basis, allowing for continuous and indiscriminate poisoning of animals throughout a wide area. In addition, the pesticide industry’s standard practice uses aggressive marketing of long term contracts as an effective solution for business and property owners dealing with rodent problems. This business model has resulted in these extremely potent poisons becoming pervasive in the wildlife food chain. While public awareness of the problem is growing, this out of sight out of mind approach to pest management, along with a powerful pest control lobby in this country, which has influenced the outcome of legislation aimed at banning and restricting SGAR use, has created a silent ecological crisis.
There are safer and more effective solutions to rodent control. A more humane and sustainable approach needs to take into account that predators and prey animals have evolved to coexist and have a right to do so. A business model that results in long term and widescale secondary poisoning of wildlife is not acceptable. To learn more and find out how you can get involved, here are some resources.
Protect our Wildlife
Project Coyote
Sierra Club Vermont Chapter
Raptors are the Solution
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