Most early mornings in the spring and fall, as he has done for more than four decades, David Willard goes out to gather the dead. A retired curator of birds at Chicago’s Field Museum of Natural History, Willard walks the mile from his office, in the dark, to pick up the thrushes, warblers, sparrows, and other migrating birds that have met their end against the glass walls of McCormick Place, a giant modernist rectangle on the Lake Michigan shore. The dead birds go into a plastic grocery bag. Those that are stunned but still alive he slips into a paper sandwich bag, to be released later in the brush on a nearby hill.
Originally built in 1960 in a city park, McCormick Place is the largest convention center in North America. Thanks to the diligence of Willard and his colleagues, it has also earned a wide reputation as a killer of birds. On a good day during migration season, he might find half a dozen dead birds; on a bad day, maybe 100. Earlier this month, a rare combination of weather and migratory patterns brought clouds of birds flying down the Lake Michigan shore. Willard found 966 dead at McCormick Place, mostly warblers. Nearly 100 others had hit the building but were still alive. “It was scary,” Willard said.
At night, bright lights both disorient and attract birds. At dawn, window reflections of trees and sky lure them to their death.
Bird collisions are a growing problem in the United States — and the world over. Four years ago, scientists reported that the number of birds in North America had declined by nearly 3 billion, or almost 30 percent, over the previous half century. Scientists say one obvious cause is habitat loss; a less obvious cause is our modern obsession with glass walls and windows. According to estimates published in the journal The Condor in 2014, building collisions kill hundreds of millions of birds each year in the U.S. and reduce the total number of birds by 2 to 9 percent. In Chinese cities, where glass buildings have also proliferated, scientists noted in a recent letter to Science, bird collisions “are now an important global factor in bird mortality.”
At the same time, there are growing efforts across the U.S. and Canada to reduce collisions and make cities more bird friendly. Businesses in more and more cities are taking part in “lights out” programs that ask building managers to dim lights during spring and fall migrations. Architects are designing buildings that reduce bird collisions, sometimes by using glass that birds can see and avoid. And more and more communities — from big cities like New York to smaller communities like Lake County, Illinois — are adopting ordinances that require bird friendly glass in new construction.
The problem of bird collisions has two aspects: glass and lights. Migrating birds fly mainly at night, and scientists say bright lights both disorient and attract them. When day dawns, window reflections of trees and sky lure birds to their death. Under some conditions, glass is invisible to birds, and they hit it while aiming for spaces beyond. It’s an issue not just for brightly lit downtowns but also for buildings away from city centers, including rural and suburban houses. While lights at any height can attract and disorient birds, most collisions happen on the lowest floors. Indeed, most birds don’t die on the upper levels of skyscrapers but in low-rise commercial districts and residential neighborhoods.
Events like the mass collisions in Chicago this month — it’s not the only one of its kind — have drawn new attention to an old problem, inspiring bird lovers, conservationists, architects, and others to try to make cities safer for birds. One of these efforts focuses on persuading businesses and building managers to dim exterior lights during migration periods, to shield upward-facing lights and, as much as possible, to turn off interior lights. Chicago was the first U.S. city to start a Lights Out program in 1999, following the example of Toronto, whose program started in 1995. The movement has now reached 48 U.S. cities.
Cities and even some smaller communities are adopting ordinances that require bird-friendly glass.
Meanwhile, groups of volunteers monitor collisions, going out in the morning to pick up the dead, rescue the wounded, and identify the most dangerous buildings. In Chicago, more than 200 volunteers take turns patrolling the city’s downtown. This is labor-intensive work that’s hard to organize. New York City has a large crew of volunteers, too, but NYC Audubon has also set up an online system, called dBird, that allows anyone to report a bird collision.
A separate effort focuses on the development and use of bird-safe glass. Architects like Chicago’s Jeanne Gang are designing buildings that use fritted glass, which is factory-treated with a pattern of ceramic dots or other designs that are visible to birds. Architects have used other tricks to break up the wide panes that are especially dangerous for birds, including decorative panels that allow in light but are visible to birds.
Meanwhile, ways of treating existing windows are becoming more popular. Feather Friendly, a Toronto company, sells a vinyl film that homeowners and building owners can use to affix tiny dots to their windows. The company says its sales have increased twentyfold over the last five years. Studies suggest that window treatments work. In one study, published in 2022, a researcher applied dots to the side of glass bus shelters in Stillwater, Oklahoma, and found that they reduced bird collisions by 64 percent.
Until now, the use of bird-friendly glass has mostly been voluntary, and it’s been used mostly on public buildings like the Jacob Javits Convention Center in New York City, or at colleges and universities, including the University of Chicago dormitory towers designed by Gang. Increasingly, however, cities and even some smaller communities are adopting ordinances that require these features.
New York City passed a local law in 2020 that requires all new construction, as well as buildings whose exterior glazing is undergoing alteration, to use bird-friendly glass on floors up to 75 feet high. Washington, D.C., passed a similar ordinance that will go into effect next year. (It raises the affected height to 100 feet.) In 2022, Nashville officials, persuaded by five women involved in local conservation efforts, joined the Lights Out program under the name Bird Safe Nashville. Bridgestone Americas, the tire company whose 30-story glass headquarters dominates the Nashville skyline, signed on first; the managers of a dozen prominent buildings, including the Nashville City Center office tower, the UBS Tower, and the Life & Casualty Tower also agreed to dim their lights.
“It’s an underappreciated problem that’s causing irreparable damage to our population of birds,” says an ornithologist.
But other building owners resisted. “This is a new concept for Nashville,” said Jackie Byrom, an organizer of Bird Safe Nashville. “I didn’t know there were birds migrating over Nashville. Most people don’t.” Elsewhere, say Lights Out advocates, building managers report that turning off lights is a burden (the increasing use of motion detectors should help in this regard), and some tenants say they simply prefer to keep their lights on for security reasons and their business logos lit.
Birds collisions are not a new problem, but scientists and conservationists did not begin to take the issue seriously until the 1970s, after glass buildings became more popular. Daniel Klem Jr., a graduate student at Southern Illinois University at Carbondale, conducted the first real study of bird window strikes in the U.S. by tracking kills around that city. He estimated that mortality from window collisions, nationwide, was between 97 and 975 million birds a year, and he began advocating for solutions, like eliminating bird attractants near windows or partially covering windows. Most of his suggestions, he said, have gone unheeded.
“I believe to this day it’s an underappreciated problem that’s causing irreparable damage to our population of birds,” said Klem, who is now a professor of ornithology and conservation science at Muhlenburg College in Allentown, Pennsylvania. But “for the last 10 years,” he said, more hopefully, “things have been happening.”
David Willard, of course, has been working on the issue almost his entire life. On a recent Thursday, he arrived at McCormick Place before dawn and began to circumnavigate the three-story building. He moved quickly, peering into the shadows, scanning the concrete for small clumps of feathers.
Workers were already busy inside the building, but no light was seen from its west and north sides — which have historically seen the most bird strikes, Willard said. After the mass killing two weeks earlier, building managers had lowered curtains to block interior light. It was something that conservationists and bird monitors had long sought and a sharp contrast to that day when no curtains hung, the lights shone brilliantly into the night, and hundreds of birds perished. “Short of changing it to no glass, it’s the best thing they can do,” Willard said.
In 2021, scientists reported that dimming the lights at McCormick Place had reduced bird collisions by 60 percent.
On this day, Willard found no dead birds. But on the west side of the building, as he passed beneath a brightly lit glass walkway that leads over Lakeshore Drive, he spotted a thrush standing on the concrete, alert but unmoving. He crept up slowly behind it, then quickly snatched it up, and slipped it into a paper bag. Not far away he picked up a dead swamp sparrow, then a pine warbler, and a golden-crowned kinglet, a tiny clump of feathers weighing barely a fifth of an ounce and small enough to fit in a soup spoon.
Since 1982, Willard and others have collected nearly 160,000 dead birds from Chicago sites, about a quarter of them from McCormick Place. Researchers enter each bird’s species, sex, age, and weight into a database that they hope will give scientists insights into bird populations and migratory patterns. Volunteers then strip the birds of their feathers, and scavenger beetles consume their flesh. The skeletons go into the Field’s ever-expanding collection.
Two years ago, the long-term monitoring of McCormick Place led to a finding whose importance rivaled Klem’s work in southern Illinois in the 1970s. Convention business had slowed around 2000, and the number of dark days at McCormick Place’s Lakeside Center had increased. This allowed Willard and his colleagues at the Field Museum to compare the number of bird collisions when the building was dark to the number of collisions when it was lit. They kept track of this for two decades. In 2021, they reported that dimming the lights had reduced bird collisions by 60 percent. It was clear proof, at least on the scale of a single building, that turning off the lights could work.
“The discouraging thing is when you see that solutions, or things that make it better, don’t get implemented,” Willard said. “It’s frustrating.“ He looked north toward downtown. The lights had been dimmed in many buildings, and the city had a subdued look. But he also noticed many new glass buildings, which, he lamented, “seemed designed to kill birds.”
Willard made a round and a half, circling back to the north side to check for birds that might have hit the glass just as day dawned, then headed back to the museum. In the distance, Lake Michagan lay gray and flat in the growing light.
“I guess I’m optimistic,” he said, the birds tucked away in a backpack slung over his shoulder. “But I hate it that it takes 900 birds in one night to get people’s attention.”