Study Finds Rat Poison in Dead Eagles From Across the US

By Alex Fox, Smithsonian

09 April 21

More than 82 percent of 133 eagles tested had so-called anticoagulant rodenticides in their bodies

n the United States, the eagle is a powerful national symbol, and even though their populations are now increasing following the ban of DDT, they’re afforded protections under three federal laws. But a new study suggests that Americans trying to eradicate rodents with poison could be negatively impacting eagles across the country, reports Ian Morse for New Scientist.

The study, published last month in the journal PLoS ONE, tested 116 bald eagles and 17 golden eagles collected between 2014 and 2018 for the presence of common rat poisons known as anticoagulant rodenticides. Researchers found rat poison in 82 percent of the eagles they tested.

Though the rat poison was only determined to be the definitive cause of death in four percent of the eagle deaths, the fact that the deadly chemicals were so prevalent is still cause for concern.

“This really suggests that despite the best efforts to use these compounds wisely and minimize the opportunity for the raptor species to be exposed, they’re still somehow getting exposed,” Mark Ruder, a researcher studying wildlife disease at the University of Georgia and the paper’s lead author, tells New Scientist.

Predators such as eagles, bobcats or coyotes tend to be exposed to rat poison by eating rodents that have been consumed the toxins through poisonous bait. Most rat poisons are now what’s known as second-generation anticoagulant rodenticides, meaning they kill animals that eat it by preventing the blood from clotting and causing lethal internal bleeding. First-generation rat poisons worked in a similar fashion but were less deadly, reports Molly Taft for Gizmodo. Second-generation anticoagulant rodenticides also tend to persist longer in the body of any creature unlucky enough to eat them.

Since 2011, the Environmental Protection Agency has restricted the sale of second-generation rodenticides to commercial users such as professional pest control workers, but it’s somehow still getting into the eagles’ food.

“It’s the ability to persist in those tissues for a long time that creates the problem,” Ruder tells Gizmodo. “Being efficient predators and scavengers, eagles are more at risk for accumulating this toxin through their system, basically just by being eagles—eating dead stuff or killing things and eating them.”

The precise health impacts of non-lethal exposure to rat poison are currently unclear, Ruder tells New Scientist, but the finding that the issue is so widespread remains “alarming.”

Scott Edwards, an evolutionary biologist at Harvard University who was not involved in the study, tells Megan Marples of CNN that the paper suggests “we are unnecessarily killing some of our most majestic bird species," and adds that "humans need to understand that when those compounds get into the environment, they cause horrible damage to many species, including our national symbol, the bald eagle.”

Speaking with Gizmodo, Ruder says his study’s findings show that deadly rat poison is still finding its way into the broader environment despite regulation. From here, Rudy tells Gizmodo “we need to keep examining what pathways for exposure are for wildlife and figure out how to lower that risk.”