From late November 2024 to the end of August 2025, Save Massachusetts Wildlife contributed funds for the liver panel testing of dead animals in the Boston metro area in order to determine if they had been exposed to anticoagulant rodenticides (ARs) and see if that exposure contributed to their deaths. Specifically, Dr. Leef of HEAL veterinary clinic performed necropsies (animal autopsies) on animals brought to her clinic, removed their livers, and sent them to Kansas State University’s pathology laboratory. The results offer insight to the extent of the issue of rodenticide poisoning in the Boston MetroWest area.
Over the 9-month period, approximately 50 animals were tested who came from either Arlington or a half-dozen nearby communities (Belmont, Lexington, Somerville, Cambridge, Brookline, and Wayland). Many of these animals were brought to HEAL’s clinic by folks in the community who discovered them in their yards or nearby parks. Other animals were brought in by municipal Animal Control Officers (ACOs) or licensed state and federal rehabbers when an animal in their care perished after suffering from symptoms of AR exposure. Yet other animals were brough into HEAL for treatment but sadly did not make it. HEAL paid KSU for the liver testing and Save Mass Wildlife would reimburse HEAL to defray the costs the clinic incurred.
Nearly every single animal tested positive for exposure to Anticoagulant Rodenticides (ARs). Almost all of the animals tested at or (often well) above the threshold that begins lethal rate of exposure for birds of prey (100 parts per billion). Most of these animals had AR levels in their livers that began at 300-400 ppb, while many others were 700-900 ppb. Additionally, almost all of the animals had some sort of bleeding issue found during the necropsy (if it wasn’t already evident from the outside), often severe internal hemorrhaging. Anticoagulants stop the blood from clotting, so most animals who have lethal range of exposure, tend to die from internal bleeding.
Red-tailed hawks and barred owls were by far the most common casualties in our data set–compromising near-equal shares. Other animals that died of AR poisoning included several Great Horned Owls, an Eastern Screech Owl, several Cooper’s Hawks, a Saw-Whet Owl fledgling, an adult Eastern Coyote, an Eastern Gray Squirrel, and an Eastern Chipmunk. More surprising findings included a Great Blue Heron and a Snapping Turtle–the first lethal cases of either species to be confirmed in the state. During the summer of 2025, a young coyote pup found on the campus of Brandeis University suffering from severe mange was admitted to HEAL clinic but later perished. A necropsy found widespread internal bleeding and liver testing found the highest exposure rates of any animal tested in this dataset at 1,400+ ppb. Also during the summer, a rare gray fox from Arlington–which has recently been designated a “Species of Greatest Conservation Need” by the State Wildlife Action Plan–died from significant internal bleeding, noted in her necropsy. She had the second highest AR exposure rate (1,168 ppb) in the dataset and fatal levels of the First Generation Anticoagulant Rodenticides (FGAR), chlorophacinone. And while the levels didn’t reach lethal range, a shrew and songbird (grackle) tested positive for more than trace levels of AR exposure–which has implications for how thoroughly ARs are infiltrating the food web.
This project was inspired and builds on the work of Cape Ann Wildlife, which necropsies raptors that die of suspected SGARs poisoning in or en route their care. We have combined our data, which can be viewed here. Cape Ann Wildlife’s data can be viewed separately here.
