Rodenticide poisoning poses threat to New Hampshire wildlife

NH wildlife including owls, bald eagles, red-tailed hawks, bobcats, and fishers are testing positive, becoming ill, and dying from eating mouse and rats that have been killed with rodenticides, according to New Hampshire Audubon.

“Consumers are not aware of how extensive this problem is, and we are desperately trying to get the word out,” said Carol R. Foss, Senior Advisor for Science and Policy for New Hampshire Audubon. “This is affecting animals everywhere in our state.”

Foss spoke about the dangers and impact of rodenticides on wildlife on Wednesday night at the Francestown town offices. The talk, sponsored by the Francestown Recreation Commission, was attended by about 30 people.

Foss encouraged homeowners and property manages to interview exterminators about what methods they will use to eliminate mice and rats before signing a contract.

“There are alternatives to these poisons, and reponsible licensed applicators will try every other option before resorting to these rodenticides. They should be absolutely the last resort,” Foss said. “Find out what is in those black boxes. It could be a snap trap, but it could be rodenticide.”

A 2023 study found that 14 of 15 fishers, 31 of 34 bobcats, 11 of 11 red foxes and nine out of nine gray foxes tested by Fish and Game were positive for SGARS, or second-generation anti-coagulant rodenticides. The poison can remain in the livers of rats for up to a year.

According to N.H. Audubon, SGARS exist in many rodenticides commonly used by professional exterminators, including Mouser, Rat-Tak, Talon, Maki Mini Blok, Contrac, Di-Kill, First Strike and Hombre.

“Mice survive for several days after eating SGAR bait. The rodenticide breaks down slowly and accumulates in the liver and other tissues, and then predators and scavengers consume the poisoned rodents,” Foss said.

Wings of the Dawn Wildlife Rehabilitation in Henniker is collaborating with NH Audubon on a mortality study of New Hampshire’s birds of prey. In 2025, the facility treated 20 red- tailed hawks, 14 barred owls, five bald eagles, 12 broad-winged hawks, and two Great Horned Owls, as well as other species, with rodenticide poisoning. Most did not survive.

“There is a very high mortality rate with animals that ingest rodents who have eaten these poisons. All five of the bald eagles died,” Foss said.

Foss said many raptors come in to Wings of the Dawn “already bleeding at the mouth.”

“If they are bleeding from the mouth, they have to be euthanized,” she said.

Foss showed a slide of a local owl’s nest with dead chicks.

“These baby owls died on Saturday, April 11,” she said. “The mothers bring poisoned rodents back to the nest, and the nest fails.”

Fishers are especially impacted by rodenticides. The UNH College of Life Sciences and Agriculture, N.H. Fish and Game, the N.H. Trappers Association, and the N.H. Veterinary Diagnostic Lab are collaborating on a fisher mortality study, using radio telemetry to track fishers across the state and undergo tissue analysis of trapped animals. According to existing data, 80% of trapped fishers test positive for rodenticides.

Foss said Hillsborough County, which includes Manchester and Nashua, has the highest rate of indications of poisoning in predators and raptors in the state.

Data from Concord Area Veterinary Services indicates that rodenticide poisoning is also a risk for domestic dogs.

“In these cases, the dogs usually ingest the poison directly, because people have left it where dogs can access it,” Foss said.

Alternatives to poison

According to N.H. Audobon, rodenticides do not provide a long-term solution to mouse and rat infestation.

“Mice evolved to resist the first-generation anti-coagulant rodenticides; and they will just keep coming back,” Foss said.

N.H. Audubon advocates for “non-poison integrated pest management,” which prioritizes excluding rodents from dwellings; starving rodents by removing food sources, targeting rodents with snap traps, contraceptives, CO2 sprayers, and nontoxic deterrents such as Rat-X; with anti-coagulant poisons used only in severe infestations, and only when monitored by professional applicators.

“The simplest thing people can do is keeping rodents out, and keep food away from them,” Foss said.

Foss said steel and copper wool are simple but effective ways of stopping gaps where mice can get in. She also recommended “old fashioned” methods such as snap traps for mice and professional rat terriers for combatting rat infestations.

“There is a lady in New Hampshire who will bring a team of rat terriers to serious rat infestations. I saw four of them kill 150 rats at one site,” Foss said.

Foss said she had spoken to at least one licensed applicator who had had to remove dangerous amounts of rodenticide from a private home while assessing an infestation.

“People do not read the directions,” Foss said. “These chemicals can be very dangerous in the hands of the general public.”

In 2023, the New Hampshire Task Force to Review Rodenticide Impact on Wildlife advocated for further research and to consider implementing revisions of product label to identify state-specific restriction of SGARS.

N.H. Audubon supports two bills in the New Hampshire Legislature, which would prohibit the use of some SGARS (HB 1018) and limit consumer access to certain high-risk rodenticides (HB 1676).

For more information go to nhaudubon.org/policy/rodenticides. For information about Wings of the Dawn wildlife rehabilitation center and bird sanctuary, go to wingswildlife.org.