Zoo releases final necropsy results on Flaco the owl's death

Flaco, the Eurasian eagle owl who escaped from his vandalized Central Park Zoo enclosure in February 2023, had high levels of rat poison in his system and was suffering from "severe herpesvirus" that he contracted from eating pigeons when he died last month in Manhattan.

The post-mortem necropsy report was released Monday afternoon by the Wildlife Conservation Society (WCS), which runs New York City's Central Park Zoo, revealing its findings regarding what caused Flaco's demise on Feb. 23 of this year, when he was found critically injured in the courtyard of a residential building on the Upper West Side of Manhattan.

"Bronx Zoo veterinary pathologists determined that in addition to the traumatic injuries, Flaco had two significant underlying conditions. He had a severe pigeon herpesvirus from eating feral pigeons that had become part of his diet, and exposure to four different anticoagulant rodenticides that are commonly used for rat control in New York City," according to the statement issued by the Wildlife Conservation Society. "These factors would have been debilitating and ultimately fatal, even without a traumatic injury, and may have predisposed him to flying into or falling from the building."

Zoo officials said the identified herpesvirus can be carried by healthy pigeons but may cause fatal diseases in birds of prey, including owls, who can be infected by eating pigeons.

"This virus has been previously found in New York City pigeons and owls," the WCS statement said. "In Flaco’s case, the viral infection caused severe tissue damage and inflammation in many organs, including the spleen, liver, gastrointestinal tract, bone marrow, and brain."

No other contributing factors to Flaco's death were identified by "the extensive testing that was performed," the WCS said.

"Flaco’s severe illness and death are ultimately attributed to a combination of factors – infectious disease, toxin exposures, and traumatic injuries – that underscore the hazards faced by wild birds, especially in an urban setting," the zoo official said.

Toxicology testing also revealed trace amounts of DDE, a breakdown product of the pesticide DDT, the WCS said.

"But the levels detected in Flaco were not clinically significant and did not contribute to his death," the WCS said. "Although DDT has been banned in the United States since the early 1970s, it and its breakdown products are remarkably persistent in the environment, and this finding is a reminder of the long legacy of DDT and its dire effects on wild bird populations."

The WCS initially said preliminary results of the necropsy found that Flaco died after crashing into a building, leaving him with a "substantial hemorrhage" under the sternum and around the liver. No bone fractures were found in the initial report.

David Barrett, the creator and manager of Manhattan Bird Alert, the go-to social media site for New York City birders, told ABC News on Monday that the necropsy results "will provide some closure to many people who have been waiting a long time for these results."

Barrett, who followed nearly every move by Flaco during his year of freedom and took thousands of videos and photos of the owl, said the necropsy findings confirmed what he suspected in the final days of Flaco's life. He said that in the four days before Flaco perished, he and other birders noticed that the raptor had stopped hooting.

"Flaco seemed ill or injured in the days leading up to his death. That's another reason why I didn't think that a collision was truly the cause of death, that there had been some underlying condition," Barrett said. "So, now we know that there truly were two serious underlying conditions that Flaco had and would have been fatal to him regardless of what happened on that Friday night."

He said that while rodenticide poisoning is common among raptors, the pigeon virus was surprising because he's seen many red-tail hawks consuming pigeons, but not dying as a result.

"It seems to be the main cause of death because it was causing inflammation throughout his organs," Barrett said of the necropsy findings on Flaco.

Flaco, dubbed "the most famous owl in the world," became a cause célèbre during the year he spent as a free bird after bolting from his zoo exhibit on Feb. 2, 2023, when a vandal cut a hole in the stainless steel mesh covering his exhibit, police and zoo officials said at the time. No arrests have been announced in the vandalism, but the New York Police Department said the investigation is ongoing.

While in the wilds of the concrete jungle, Flaco continued to draw crowds while his survival and flying skills rapidly improved, and the territory he explored expanded all the way downtown to Manhattan's Lower East Side.

After committing resources to recapture the bird, zoo officials released a statement on Feb. 12, 2023, saying they were scaling back on their recovery efforts after noticing that Flaco was successfully hunting for prey.

"Several days ago, we observed him successfully hunting, catching, and consuming prey. We have seen a rapid improvement in his flight skills and ability to confidently maneuver around the park," zoo officials said at the time.