The study from the University of Georgia (UGA) examined the carcasses of 116 bald eagles and 17 golden eagles. The scientists found that 96 of the 116 bald eagles and 13 of the 17 golden eagles were exposed to rat poison.
The bodies of the birds were collected by 18 different wildlife management agencies all over the country. This showed the scientists that this is a national problem. (Related: North American bird populations pivotal to pest control and seed dispersion have decreased by 29% in the last 49 years.)
The poisons discovered in the systems of the eagles was a form of anticoagulant rodenticide, which thins the blood of and eventually kills the mice rats after they eat it.
The first generation of rodenticides was not as effective at killing mice and rats, so manufacturers made them much more potent to kill mice and rats faster. However, it also caused the rodenticides to stay in their bodies for longer periods of time. Meaning, rodenticides can enter the bodies of the predators that feed upon mice and rats.
If the eagles were to indirectly ingest the anticoagulant rodenticide in significant amounts, it can result in spontaneous internal or external bleeding and bloody urine or feces. In the worst cases of poisoning, the eagles can die from cardiovascular shock.
According to the autopsies, around four percent of the eagles succumbed to the poison – the ones that showed signs of heavy internal bleeding and were unable to form clots or scabs.
Most of the other eagles were killed by electrocution, collisions with vehicles, gunshot wounds or other causes.
The researchers believe the rat poison was found in the systems of the eagles because of their consumption of rodents or of their more natural prey that have eaten rodents.
"Although the exact pathways of exposure remain unclear, eagles are likely exposed through their predatory and scavenging activities," said Mark Ruder, assistant professor at the College of Veterinary Medicine at UGA.
Scott Edwards, a zoology professor and director of graduate studies at Harvard University, called the widespread use of rat poison unnecessary, especially since its usage may be responsible for "killing some of our most majestic bird species."
"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," said Edwards.
Insecticide poisoning was one of the main reasons why the population of eagles fell drastically during the mid-20th century, along with excessive hunting. The numbers of bald and golden eagles quadrupled between 2009 and 2019 to the more than 300,000 currently in the United States.
If rodenticide and other toxic chemicals once again become widespread in the environment, the population of bird species like the bald and golden eagles will be affected. How much it will be affected is unclear, since the current science is not certain whether the poison affects reproduction or causes any other health issues.
"This study 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," said Ruder.
Learn more about the toxic chemicals in the environment that are causing the deaths of many animals by reading the latest articles at Environ.news.