A 2020 study found anticoagulant rodent poison in every red-tailed hawk it tested—and 91% of those birds had been exposed to at least two kinds. That finding points to a hidden cost of tackling mice and rats with poison: the chemicals can move up the food chain and harm the wildlife that helps keep rodent numbers in check.
Mice and rats can spread viruses and bacteria, trigger asthma attacks and chew through parts of a home. It is understandable that people want to act quickly when rodents get inside. But some poisons, called anticoagulant rodenticides, stop blood from clotting. A poisoned rodent may die from internal bleeding, while a hawk, owl or fox that eats it can take in the chemical too.
Maureen Murray, the Shalin Liu Professor of Wildlife Medicine at Tufts University’s Cummings School of Veterinary Medicine and director of the Tufts Wildlife Clinic, has studied rodenticide effects on wildlife for two decades. “While I am often asked if some poisons are safer for wildlife, the words ‘safe’ and ‘poison’ inherently do not go together,” she said.
The evidence extends beyond red-tailed hawks. In a 2023 study of four birds of prey, 96% tested positive for anticoagulant rodenticides, and 81% had been exposed to two to four different types. The study, published in Environmental Pollution, also recorded exposure to bromethalin, a different poison that affects the nervous system. Murray and co-author Elena Cox found residues of a toxic breakdown product of bromethalin in 30% of the birds tested for it. Researchers do not yet know whether bromethalin poses a lower risk to wildlife; poisoning can also be difficult to spot because its signs resemble other brain and nerve problems.
A poisoned rodent may survive for days after eating bait, and can keep feeding in that time. Its body may then carry enough poison to harm the predator that catches it. Some chemicals collect in the liver, so predators that eat several poisoned animals can build up dangerous amounts. Red-tailed hawks, barred owls, great horned owls and red foxes are among the animals at risk.
Murray recommends starting with prevention. Keep garbage, compost, grass seed and pet food in tightly sealed containers, remove bird feeders that attract rodents, clean up pet waste and close gaps where mice can enter. Pay special attention to spaces around sink pipes and kitchen appliances, as well as cracks in the foundation.
If traps are needed, snap traps kill rodents faster than poison, Murray says. She advises against glue traps, which can leave animals suffering for hours or days and may catch birds or reptiles by mistake. Homeowners can also ask pest-control companies about integrated pest management—a plan built around prevention, repairs and clean-up, with other methods used when needed.
These steps can make a home less inviting to rodents without exposing predators to poison through their prey. Sealing an entry point and securing food may seem simple, but together they can protect both people’s homes and the wildlife that helps control mice and rats.