On March 3, on what felt like the first lovely Sunday afternoon of the year, hundreds of humans gathered at an oak tree in New York City’s Central Park to remember an owl. They carried musical instruments, television cameras, speeches and verse. One speaker took the microphone and read the crowd a rewrite of Frank O’Hara’s piece “Poem [Lana Turner Has Collapsed!],” with adjusted lines to address the departed bird: “Oh Flaco we love you get up.” Many of the mourners had been expecting the grim news that brought them to the park for a long time.

Flaco, the Eurasian eagle-owl who escaped from his Central Park Zoo enclosure at the southern end of the park and lived free in the city for more than a year, had died just over a week earlier, after apparently striking a residential building. Ornithologists and conservationists say his remarkable life as a voluntary New Yorker—and the tragic way it ended—should change the way humans think about the birds that live among us.

Hatched in captivity in North Carolina and raised at New York City’s Central Park Zoo, Flaco chose his own location for the first time on February 2, 2023, after someone created a hole in his enclosure that allowed him to escape. The 12-year-old owl eluded the humans who tried to recapture him and quickly began to behave as his wild counterparts in Europe and Asia do, hunting, hooting and swooping through the city. Zoo officials eventually suspended their efforts to bring him back to his cage and announced that they would monitor him instead. Many human New Yorkers delighted in their non-native avian neighbor: His success as a newly wild bird was proof, perhaps, that theirs was a city where anything could happen.

Flaco's Enclosure at Central Park Zoo
Flaco’s former enclosure at the Central Park Zoo has remained empty for the past year. Lauren Oster

Even as a year passed and the owl’s admirers celebrated his “Flaco-versary” of freedom, experts were cleareyed about the dangers he continued to face in the city before he died.

“He’s not in the wild, born to natural parents, living in his natural habitat; that’s the only good situation for him, and it’s never going to happen,” said Christopher D. Soucy, executive director of the Raptor Trust, a New Jersey wildlife rehabilitation center that admitted 89 owls in 2023.

“He’s most assuredly going to live a far shorter life than if he stayed in captivity,” noted Karla Bloem, executive director of the International Owl Center in Minnesota.

One particular hazard came up in every conversation: “There’s a war on rats in New York City, and they don’t do it all with traps,” said Kevin McGowan, an associate at the Cornell Lab of Ornithology. “There’s always a chance that he’ll pick one up somewhere that’s loaded with poison, and we know that secondary poisoning does kill raptors.”

The tragedy they had foreseen struck on February 23, when a building supervisor found Flaco lying in a residential courtyard on Manhattan’s Upper West Side. His improbable year had ended with his death.

When veterinary pathologists performed an initial necropsy on Flaco, their findings were “consistent with death due to acute traumatic injury.” The Wildlife Conservation Society, the zoo’s parent nonprofit, noted that “Flaco’s tragic and untimely death highlights the issue of bird strikes and their devastating effects on wild bird populations.”

Flaco the Owl Perches Near Building
Flaco favored high perches such as scaffolding and water towers as he explored Manhattan’s Upper West Side. David Lei

That issue is especially deserving of local attention, as New York City is notorious for bird fatalities. Millions of migrating birds navigate among its disorienting skyscrapers in the spring and fall as they follow the Atlantic Flyway, and each year an estimated 90,000 to 230,000 die trying. To reduce that number, humans have to mitigate the twin hazards of reflective glass windows and artificial lighting. Glass is invisible to birds, which perceive images reflected in it as food, shelter, open air and even other birds. Humans can make it visible to them with barriers in front of it or markings on its surface. Artificial lighting, in turn, attracts and disorients birds that are accustomed to navigating after dark with natural cues such as moonlight and starlight—and can precipitate fatal crashes into buildings and other obstacles.

In the wake of the zoo’s report and an uptick in public attention to avian welfare, New York lawmakers renewed local pushes to pass legislation for birds’ sake. Senate Bill S7098A, which was renamed “the Flaco Act” after the owl’s death, would require some state-owned buildings to incorporate practices to reduce bird death. Senate Bill S7663, the Dark Skies Protection Act, would require that non-essential outdoor lighting be shielded, motion-activated or turned off between 11 p.m. and 5 a.m. That said, researchers have found that between 365 million and 988 million birds die hitting buildings across the United States each year, and fewer than 1 percent of those fatalities involve high-rises. Products and practices to reduce strikes at low-rises (roughly 56 percent of deaths) and residences (roughly 44 percent) are as just as crucial to conserving birds.

Bloem notes that common equipment and barriers can also be lethal obstacles for owls and other birds. She says hockey and soccer nets, for example, should be taken down when not in active use, as owls that fly into and become entangled in them can incur life-threatening injuries as they struggle to escape. Barbed wire is a particularly grisly hazard: “Owls fly into barbed wire fences and they get impaled,” she explains. “They thrash around, they rip the muscle off their bones, [and] it’s hideous, absolutely hideous.” Adhesive pest control like glue boards intended to catch rodents and tape for lanternflies, in turn, is woefully indiscriminate. “All kinds of things get stuck on them,” Bloem says. “Anything sticky outside: bad.”

Flaco in a Tree
Flaco spent the majority of his first months of freedom exploring Central Park. At least 11 species of owls had been spotted there prior to his escape from the zoo. David Lei

American lawmakers are taking steps to prohibit that form of pest control, as their counterparts have already done in England, Iceland, Ireland and New Zealand. This January, Representative Ted Lieu, a Democrat from California, introduced a bill to ban the possession and use of glue traps nationwide.

Bloem’s colleague Marjon Savelsberg, a Dutch researcher who studies wild eagle-owls’ vocalizations in the quarry near her home in Maastricht, likens Flaco’s experience in Manhattan to that of the local members of his species she hears and sees on a regular basis. The rats, pigeons and crows attracted to litter in and around Maastricht’s city park create an area of high prey density that she says is like McDonald’s for eagle-owls. “They hunt in town, and we know they do because they’ve been fitted with transmitters—but I also know it because people [in town] send me recorded sound files,” she says. “Because I know the individuals, I can tell, ‘Oh, that’s Female No. 1 calling for food.’”

She also likens Flaco’s fate to the owls’ deaths near her home. “The last year of his life, Flaco lived the life of his wild family over here—and, sad to say, also died the way a lot of his family members here die,” she says. “We are their biggest threat: rodenticides, pesticides, PCBs, building collisions, barbed wire entanglements, habitat loss, bird flu … you name it.”

After further study of his tissues and organs, several of those threats were found to have affected Flaco. When Wildlife Conservation Society updated its initial necropsy findings after weeks of additional analyses, the new details painted an even more devastating picture of the city’s effect on Flaco. Post-mortem testing revealed that he had a severe case of pigeon herpesvirus, a disease he contracted from eating feral pigeons, and four different anticoagulant rodenticides in his system. Both the disease and the rat poisons “would have been debilitating and ultimately fatal,” and experts say they likely weakened and disoriented him, causing him to topple from his perch high in the air and sustain traumatic injury on impact with the ground rather than with the building. Testing also revealed trace amounts of DDE, a breakdown product of DDT, an insecticide banned in the United States in 1972. Though the level in Flaco’s body was clinically insignificant, it was a grim reminder of the agricultural chemical’s long shadow.

“It is a general truth that being compromised by a toxin like rodenticide or DDE makes an animal more susceptible to an opportunistic disease, whether bacterial, viral or parasitic,” says Rita McMahon, the director of the Wild Bird Fund, the Manhattan wildlife rehabilitation center that initially retrieved Flaco’s body. The organization brought him to its hospital a few blocks away, where veterinary staff pronounced him dead. Research has demonstrated rodenticides’ deadly effect on wild animals’ immune systems in California, where scientists found that bobcats exposed to multiple types of anticoagulant rat poison were more than seven times more likely to die of mange, a skin parasite that was previously rarely fatal to them, than of any other cause.

Flaco Graffiti
Street art celebrating Flaco on Manhattan’s Lower East Side appeared after he visited the neighborhood in November 2023. Lauren Oster

Wildlife rehabilitators and other experts say bacterial and viral diseases that affect pigeons—and can spread quickly in dense urban populations—also threatened Flaco. “From our very recent readings on the subject of pigeon herpesvirus, apparently the Eurasian eagle-owl is particularly susceptible to the virus,” McMahon says. “We sure make living rough for wildlife.”

Anticoagulant rodenticides, like those detected in Flaco, interfere with the activation of vitamin K, which produces blood-clotting factors in the liver. In animals without those factors, bruising, bleeding into body cavities and hemorrhaging can culminate in shock and death. It can take up to ten days for a rat that has ingested lethal levels of anticoagulant rodenticide to die from internal bleeding, and the toxins can stay in their bodies for up to 100 days. A predator consuming that rat, then, experiences the rodenticide’s effects on its own system. No matter how sheltered a source of poison might seem, its deadly impact can travel far and wide.

New York City’s best-known birds have demonstrated rodenticide’s devastating effects on their species time and time again. Pale Male, the city’s most celebrated red-tailed hawk, lost his mate to rodenticide poisoning in 2012; when he mated again later that year, rodenticide sickened two of his chicks and is thought to have killed another. In 2022, a paper in Ecotoxicology reported that 68 percent of red-tailed hawks in New York State have anticoagulant rodenticide toxins in their systems. Barry, a barred owl who captured New Yorkers’ hearts in 2021, had two anticoagulant rodenticides (bromadiolone and difethialone) in her system when she was struck and killed by a vehicle in Central Park. She was at risk for a fatal hemorrhage long before that blunt-force trauma occurred.

“What [many pest-control companies do is use] four or five different poisons, not just one, and if you’re adding a blood thinner to a blood thinner to a blood thinner to a blood thinner, you’re going to end up with water for blood, which is exactly what happens to these animals,” says Lisa Owens Viani, director of Raptors Are the Solution, a California-based nonprofit focused on eliminating toxic rodenticides from the food web. In Flaco’s case, the rodenticides in his system could have turned a nonlethal injury into a fatal one. “This happened to an owl in San Luis Obispo a couple years ago; she had a small wound that ended up bleeding out. When they necropsy these animals, the body cavity is often just filled with blood. The photos are very hard to look at,” Viani says. Furthermore, “If you’re flying around with thinned-out blood, you’re anemic, you’re weak, you’re not going to be able to dodge the normal kinds of things you would have to dodge.”

Flaco Perches on a Building
Eagle-owl researchers in Europe speculate that Flaco used Manhattan’s massive buildings to amplify the sound of his hoots. David Lei

Citizens and conservation groups are pushing lawmakers to curb rodenticides. New Yorkers took a stand on birds’ behalf in 2014, when six nonprofits filed a petition with the state’s Department of Environmental Conservation to regulate the use of second-generation anticoagulant rodenticides (SGARs). It was denied that fall, a move that the pest-control industry celebrated by commending colleagues who had lobbied against the bill in Albany.

The U.S. Environmental Protection Agency stopped licensing SGARs for sale to general consumers nationwide in 2015. That said, retail customers in many parts of the country can still buy the first-generation poisons, which act more slowly but are just as harmful. Furthermore, pest-control professionals can still use SGARs in all U.S. states except California, where loopholes exist for industrial uses. Already-purchased products or those that weren’t removed from store shelves are also still deployed. “People are still somehow using them,” veterinarian Cynthia Hopf-Dennis, the lead researcher on the Ecotoxicology study on rodenticide in red-tailed hawks, told the Cornell Chronicle.

On the legislative level, Viani and her fellow conservationists in California were able to push for the passage of rodenticide-regulation bills such as 2020’s California Ecosystems Protection Act (AB 1788) and 2023’s AB 1322. They filed lawsuits to force the state to investigate the wide-ranging impacts and cumulative effects of those poisons and presented groundbreaking research—such as the aforementioned study on bobcats—and stated that moratoriums shouldn’t wait. Agencies for environmental regulation vary from state to state, but that grassroots effort in California demonstrated that local groups working together could have a far-reaching impact, says Viani.

On an individual level, experts say concerned citizens can take immediate action to reduce threats to birds living in their communities. Raptors Are the Solution offers downloadable outreach materials and an Activist Toolkit with step-by-step instructions for reducing rat poison use and introducing safer integrated pest-control strategies and long-term solutions to infestations.

Eurasian Eagle-Owl Chicks
These four Eurasian eagle-owl chicks have been borrowed from their nest for leg banding, which will allow Belgian ornithologists to track the health of their population over time. Didier Vangeluwe

Didier Vangeluwe, the head of the Royal Belgian Institute of Natural Sciences’ bird banding center and an ornithologist who has studied eagle-owls for 40 years, emphasizes the importance of lobbying local authorities to expand cities’ green areas and improve their plant diversity and water quality. He also stresses that managing the balance and health of nonhuman species is our responsibility, whether we acknowledge it or not. “We are in the center of the game, and our influence is going in every direction,” he says.

Raptor Trust director Soucy concurs that we should make human habitations safer for wild animals, and that we should be doing it now. “Millions and millions and millions of years of evolution didn’t really design these animals to live in urban environments,” he says. “Some of them don’t have a choice anymore, because we’ve messed up so much of their natural environments; they’ve moved in not necessarily by choice but out of necessity. We have to do our best to understand that we’re sharing the world with them.”

Get the latest Science stories in your inbox.

Lauren Oster is a writer in New York City.