A necropsy on the body of Flaco, the famous Eurasian Eagle-Owl that captivated New Yorkers, has revealed a grim and sobering reminder of the impacts of pesticides on wildlife. While traumatic injuries from a window collision — an all-too-common occurrence that kills hundreds of millions of birds each year — ultimately caused Flaco's death, the well-loved owl was also found to be carrying lethal levels of rodenticide. For over a year, Flaco had survived outside of the Central Park Zoo after his enclosure was vandalized and he got out.

When he collided with a glass window of a building in New York City's Upper West Side in late February, the extremely high levels of anticoagulant rodenticide in his system were likely debilitating. This kind of rodenticide works by thinning the blood and preventing coagulation. At low levels, a bird that has ingested rodenticide may appear sluggish, weak, and disoriented. Higher levels of exposure can cause bleeding and lead to shock and death in animals. The effects of rodenticide can linger in the body for months and compound over time as the animal ingests more poison. They can cause seizures, kidney failure, muscle weakness, and eventually, death.

“Flaco's death tells a story all too familiar for raptors: habitat loss drives adaptation to urbanized areas, and urbanized areas attract rodents, which people want to control with chemicals,” said Hardy Kern, American Bird Conservancy's (ABC) Director of Government Relations. “Flaco's death is indicative of the unintended consequences of rampant overuse of these chemicals.”

The widespread use of pesticides (the umbrella term encompassing insecticides, rodenticides, and other related products), whether used to control mice or combat weeds, has profound and cascading effects. The consequences of these poisons can ripple out far beyond their intended targets. Rats and mice that have ingested rodenticides tend to move sluggishly, making them easy targets for birds of prey. For a bird of Flaco's size — the Eurasian Eagle-Owl is one of the world's largest owl species, with a wingspan that can reach an impressive six feet — one poisoned rat may not have killed him, but the accumulation over time can be deadly. The necropsy and toxicology testing by the veterinary team at the Bronx Zoo revealed Flaco had ingested four different rodenticides with anticoagulant properties. He was also carrying high levels of pigeon herpesvirus, a virus carried by healthy feral pigeons that can be harmful to birds of prey, causing inflammation and damaging tissue. 

“When four different anticoagulants are found in the same bird, we can't ask for a clearer need for action,” said Kern. “Sadly, this illustrates the impacts these chemicals have on native birds of prey like Red-tailed Hawks and screech-owls. We need to reduce our dependence on anticoagulant rodenticides. Viable alternatives exist and numerous strategies are possible.”

Flaco's toxicology testing also showed the presence of a substance that has been banned in the U.S. since the 1970s: DDE, a breakdown of the agricultural pesticide, DDT. A massive effort, spurred on by the publication of Rachel Carson's Silent Spring, led to the banning of the pesticide. DDT weakened the eggshells of birds like the Brown Pelican and Peregrine Falcon, leading to precipitous declines for some species that are still recovering today. The presence of this DDT breakdown product in Flaco's blood decades later is a chilling reminder of the long-lasting effects of human actions on wildlife and the environment. 

Today, common pesticides pose a similarly grave threat to birds and other wildlife. ABC has championed regulations for harmful pesticides and continues to push for a safer regulatory process for these chemicals. Regulations are just one part of the solution to the pesticide problem. Join ABC in taking action on pesticides to protect birds from the painful and avoidable ends of birds like Flaco. Avoid the use of pesticides at home and let your representatives in Congress know you support closing loopholes in pesticide regulations.

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American Bird Conservancy is a nonprofit organization dedicated to conserving wild birds and their habitats throughout the Americas. With an emphasis on achieving results and working in partnership, we take on the greatest problems facing birds today, innovating and building on rapid advancements in science to halt extinctions, protect habitats, eliminate threats, and build capacity for bird conservation. Find us on abcbirds.org, Facebook, Instagram, and X/Twitter (@ABCbirds).

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