Rat Poison Threatens Many MA Birds Of Prey, Experts Say

NATICK, MA — State wildlife officials have documented the first death of a bald eagle in Massachusetts due to rat poisoning, a growing problem that experts say affects several important bird species across the state.

The bald eagle was living in a nest along the Charles River in Middlesex County, and was spotted in March behaving strangely. Within a few days, the female bald eagle was dead, MassWildlife said this week. A necropsy at the Cummings Veterinary Medical Center at Tufts University confirmed the eagle died after ingesting second-generation anticoagulant rodenticide — a common rat poison used by pest control companies and sold online in large quantities.

Wildlife scientists have long known that rat poison is a threat to predators like bald eagles, red-tailed hawks and owls. But recent research conducted in Massachusetts has shown the problem may be getting worse.

Dr. Maureen Murray, director of the Tufts Wildlife Clinic at Cummings Veterinary Medical Center in Grafton, began studying the problem around 2006. Murray has since published three papers about rodenticide exposure in raptors. Between 2012 and 2016, she tested 94 birds for rat poison exposure, and 96 percent were positive. In a more recent study of 43 red-tailed hawks, every bird Murray tested was positive for rodenticide exposure. This spring, a nationwide study published in the journal PLoS ONE found that 82 percent of more than 100 bald and golden eagles tested between 2014 and 2018 were exposed to rat poison.

Scientists do not know exactly how the birds are ingesting poison. There's a difference between birds that have been exposed to the poison and ones that show symptoms of poisoning, which typically involves hemorrhaging blood — and possibly death. It's possible raptors are preying on rodents that have been poisoned, making them secondhand victims.

"We don't exactly understand the route these rodenticides take through the food chain," Murray said.

It's also hard to estimate how many birds are dying. Scientists can't count birds that might be dying out in the wild. They also don't count birds who died by another cause, like getting hit by a car, but tested positive for poison.

The problem is also widespread. Murray has studied birds exposed to rat poisoning from every part of the state and outside Massachusetts. (State officials declined to say where the bald eagle that died in March was living along the Charles River, saying that releasing the information could endanger nests.)

A possible fix for the problem: stop using rat poison. It's more work, but rodent infestations can be better controlled by better waste management, and by finding and closing rodent entry points around buildings, Murray says.

"If rodent poisons were the answer to rodent problems, we would've solved it already," Murray said.

Bald eagles have made a major comeback in the U.S. since the 1960s, when chemicals like now-banned DDT reduced the population to under 500 nesting pairs across the nation. There may be as many as 71,400 nesting pairs today, according to the U.S. Fish & Wildlife Service. But bald eagles and other birds of prey still face man made threat, be it from lead bullet fragments or common household rat poison.

"Doing all those basic steps toward sustainable long term rodent management will go a long way toward protecting our wildlife," Murray said.

Have you seen a bald eagle recently? MassWildlife wants to know. The agency is looking for reports of bald eagles exhibiting nesting behavior, like flying while carrying sticks or sitting in a nest. Contact mass.wildlife@mass.gov with tips, and make sure to note if the bird was wearing a color-coded leg band.