Memorials sprang up in New York City over the weekend in honor of Flaco, a Eurasian eagle-owl who died on Friday after apparently striking a building on the Upper West Side.
His ability to thrive for a year in Manhattan after escaping from the Central Park Zoo last February captivated much of the city, offering an enchanting object lesson about the power of instinct and the beauty of urban wildlife.
His death may prove equally instructive.
Flaco is among the estimated one billion birds that will die this year in the United States after striking buildings.
Building strikes are one of the main causes of death for birds — and one of the easiest threats to solve, according to Christine Sheppard, director of the glass collisions program at the American Bird Conservancy.
“This is one conservation issue where we know exactly how to fix it,” Ms. Sheppard said. “We just need to get people to do it.”
Here’s what to know about why birds strike glass windows and some of the ways humans can help:
Why do birds crash into windows?
Most species of migrating birds travel at night. Cities’ artificial light draws them in, disorienting the birds and making them more prone to collisions with windows that, in the daytime, reflect vegetation and open sky.
A study published in The Wilson Journal of Ornithology concluded that between 621 million and 1.7 billion birds die in the United States each year because of building strikes. New York City Audubon’s scientists estimate that about 250,000 birds die in the city each year after such collisions.
The problem is most acute during the spring and fall migrations and mainly affects small migratory songbirds.
What kinds of buildings are most dangerous?
Buildings with lots of windows are most problematic.
And shorter buildings — not skyscrapers — account for the most bird deaths. About 56 percent of deaths from building collisions were linked to low-rise structures, and 44 percent occurred at private residences, according to an evaluation of 23 studies.
Windows that are less than 100 feet from the ground are most likely to reflect vegetation and to give birds the impression of flying toward a tree or the open sky.
“Birds don’t see glass,” Jessica Wilson, executive director of NYC Audubon, said. “What they see is what’s on the other side or what’s reflected.”
In this regard, Flaco’s death may be atypical. He was found in the rear courtyard of an eight-story building on West 89th Street surrounded by buildings. Neighbors had recently spotted Flaco roosting on fire escapes during the day and hooting at night.
Flaco was nearly 14 years old and had lived most of his life at the Central Park Zoo. He had roamed free since last February after someone cut open the mesh on his enclosure in an act of vandalism that remains unsolved.
The Central Park Zoo, in its initial report, said that Flaco had died of acute traumatic injury, but further tests would determine whether he had been exposed to toxins or infectious diseases. “Flaco’s tragic and untimely death highlights the issue of bird strikes and their devastating effects on wild bird populations,” the zoo said in a statement.
Alan Drogin, a longtime birder who is on the board of the Linnaean Society of New York and lives in the building near where Flaco was found, was one of the first people to tend to the owl after he was discovered near a basement door Friday evening.
Mr. Drogin said ill health or poisoning from rodenticides might have contributed to Flaco’s death, and he warned against concluding that the owl’s death was typical of bird deaths related to building collisions. “We should wait until the full autopsy,” he said.
What have cities done to make buildings safer?
San Francisco, in 2011, was the first U.S. city to use legislation to curb building collisions, and many other cities, including Chicago and Philadelphia, have since adopted laws to address the problem.
In 2019, New York City passed the country’s most comprehensive collision-proofing legislation, requiring builders to use bird-friendly material in all new construction and large renovations.
New York City also requires nonessential outdoor lights at city-owned and city-managed buildings to be shut off at night during peak migration months.
Even before New York City ’s 2019 legislation was adopted, the Javits Center, once considered one of the deadliest buildings for birds in New York, took steps that are now considered a national model. New glass panels imprinted with patterns visible to birds have cut deaths there by 90 percent.
What else do experts recommend?
People who find dead birds are encouraged to report them to dbird.org. The crowdsourced data is used to identify problematic buildings across the country — and to offer solutions.
In New York, Circa Central Park, a residential building with dazzling views, was one of the top three deadliest structures among those monitored by NYC Audubon in 2022.
Last year, the condo board decided to spend $60,000 to add translucent dots to windows to make them more visible to birds.
How can New Yorkers make their homes more bird-friendly?
There are many low-cost ways to make homes less dangerous for flying birds.
Large windows and glass doors nearest bird feeders and fruit plants are often the deadliest. Stickers or tape visible from at least 10 feet away can be placed on the exterior of the glass to offer visual cues to low-flying birds. (A study published last year showed that decals affixed to the inside of windows were not effective.)
“If you like birds enough to want to put food out for them,” Ms. Sheppard said, “you should make the glass you’re looking through safe for them.”
