One October night, a massive flock of birds swept across the Chicago skyline, stunning binoculars as they shone with yellow, white, and brown lights across the sky. It was an incredible moment for birdwatchers, but the next day, nearly 1,000 dead birds were found strewn outside a building along Lake Michigan, and many more were found scattered across Chicago's streets.
Migratory bird experts said the unusually large die-off was the result of several common events happening at once. One factor, they said, was easily preventable: the large number of buildings that had their lights on on the night of October 4, disorienting the migratory birds.
While there have been major changes at McCormick Place Lakeside Center, the building with the highest concentration of dead birds since October, bird-safety advocates are exploring measures to protect birds throughout the city, such as installing bird-friendly film on windows, blocking windows with shutters or curtains, and turning off decorative lights at night during bird migration season.
Judy Pollock, president of the Chicago Birding Society, said the changes at McCormick Place are great, “but there are a lot of other buildings out there that need to do something about their windows,” she said.
Chicago Bird Collision Monitors, a volunteer group that retrieves dead birds and rescues injured ones, found 1,600 dead and injured birds in an area of ​​less than two square miles of downtown on October 5, said Annette Prince, the group's president. Because the group doesn't cover every neighborhood, Prince said there could be thousands more dead or injured birds in the city because birds may have collided with buildings after volunteers left.
Chicago's central location means it's one of the busiest cities for migratory birds in the U.S. A study published in April 2019 in the journal Frontiers in Ecology and the Environment named Chicago, along with Houston and Dallas, among the most dangerous cities for migratory birds.
Bird-safety advocates have long been trying to get Chicago to pass an ordinance similar to New York City's that would require new buildings to be bird-safe, with the ultimate goal being to require bird-safety for all buildings, new and old.
In April, the Chicago Department of Planning and Development released a draft sustainable development policy that includes updated bird protection standards, but it is voluntary, not mandatory (the policy is expected to be implemented in the coming months).
“We feel like Chicago is a huge threat to birds,” Prince said, “but they're not going to do anything about it yet.”
The voluntary standard includes protecting parts of buildings that are especially vulnerable to bird strikes, such as glass railings, decorative panels and awnings, with materials such as decals and wood that allow birds to see better than highly reflective or transparent materials.
The standards also recommend that there should be a minimum distance of 20 feet between glass walls of buildings and outdoor pools or fountains, and that decorative lighting during migratory bird season be controlled so that it can be turned off between 11 p.m. and midday. Occupants of high-rise buildings should also be encouraged to turn off lights or close blinds after 11 p.m., the guidelines said.
Peter Strazzabosco, deputy director of the Chicago Department of Planning and Development, said in an email that mandatory standards would require City Council legislation.
The Sustainable Development Policy awards points to new developments based on what sustainability criteria they adopt to meet the required standards. The 2024 update places a higher value on bird protection than ever before. “The Department of City Planning recognizes that Chicago's location along major flight paths poses dangers to migratory birds,” Strazzabosco said. The department hopes that by increasing the point value of bird protection, more new developments will adopt bird protection, he said. In the past, about 10 percent of projects chose bird protection, he said.
More than 54.7 million birds flew over Chicago during this year's spring migration, without the mass die-offs that occurred last fall.
Winds were bad for migratory birds in the days before what some birdwatchers call the “Chicago Megaflight,” so many of them waited outside the city for conditions to improve, said Benjamin Van Doren, an assistant professor who studies migratory birds at the University of Illinois at Urbana-Champaign and worked on a 2019 study of cities dangerous to migratory birds.
When the weather became safe for flights outside the city, large numbers of the birds headed south and encountered severe thunderstorms. As the birds flew lower to avoid the storm and find land, they encountered hazards such as Lake Michigan and the city's well-lit buildings.
Another danger was the McCormick Place Lakeside Center, an events center along the shore of Lake Michigan that is covered in glass the size of about two football fields. The building was lit up for an event when the crash occurred, and about 1,000 birds were found dead outside.
David Willard, former collections manager for the bird collection at Chicago's Field Museum, has monitored bird strikes at McCormick Place since 1978, making the building an extremely rich resource for studying dangers to birds.
During migratory bird season, Dr. Willard or another museum representative walks the perimeter of the building around dawn, looking for birds that have crashed into the building. Over the years, the Field Museum has collected more than 40,000 dead birds (and rescued another 4,000-4,500 that had been stunned).
Dr Willard said that in more than 40 years his team had never found as many birds as they did that October day. The birds were still running into buildings well past dawn, he said. “It's like, if you put a brick wall in front of them, they would still run into it,” he said.
According to Dr Willard, most of the 977 birds killed were warblers. The most numerous were palm warblers, of which there were over 300, followed by yellow-banded warblers. Other bird species included soaring warblers, blue buntings and warblers. A further 100 birds were found stunned and were later released from the building.
After the bird's death, representatives from McCormick Place accompanied Dr. Willard on a walk around the property, and the building owners also consulted with bird experts, including the U.S. Fish and Wildlife Service.
Lalita Clark, CEO of the Metropolitan Pier and Exposition Authority, the city corporation that owns McCormick Place, said the authority plans to install window film that paints patterns birds can see. Clark said the film will cost about $1.2 million and the authority aims to have it installed in time for the fall migratory bird season. The group also considered buying motorized curtains or blinds but decided that would be too expensive.
Clark said the building also participates in the “Lights Out” program, which encourages buildings across the country to turn off or dim their lights at night during migratory bird season. At McCormick Place, curtained windows are kept closed all day, and once events are over and people are gone, the lights are dimmed to 25 percent.
Dr Van Doren said policies to reduce or eliminate lighting from buildings were a simple way to reduce bird deaths.
“This is a really big problem, but it's also one that can be easily addressed and has an immediate impact if we come together and work on it,” he said.