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The death toll was like nothing Stephen Maciejewski had ever seen. Early on October 2, 2020, the ���Ϲ��� Mid-Atlantic volunteer began scooping up bird carcasses dotting Philadelphia streets for scientific collection. He put each one in a separate plastic bag and labeled them—date, time, location of death—until he ran out of bags. Overwhelmed, he phoned Keith Russell, the organization’s urban conservation program manager, who came to help.

It was peak migration season, and the victims, attracted by nighttime lights, had collided with buildings. In all, the official single-day death toll estimates topped 1,000 birds, with many thousands more likely unaccounted for. They are among the hundreds of millions—mostly migrants—estimated to die from such collisions in the United States annually.

Using the data and photos from that morning, Maciejewski and Russell inspired an article in the Philadelphia Inquirer. From there, the story spread to media outlets in other states and across the world. “With all of this publicity generated, we felt this would be an excellent time to try to do something to leverage this, to make better conditions for birds that are migrating,” Russell says.

The tragedy inspired ���Ϲ��� chapters, a local ornithology club, and a museum to create in 2021. Their biggest achievement: Starting a program to dim the city’s night skies during migration’s most hazardous hours.

Philadelphia conservationists tried to start a Lights Out program in 2006, but building managers wouldn’t participate without hard proof of the problem. To gather evidence, volunteers documented building collisions from 2008 to 2011 using grant funding. In the following years, collision monitoring stopped, but used the data to advocate for bird-safe practices citywide. Through monitoring, “we can have more data, and we can say to people, ‘This is not just hearsay,’” Maciejewski says. “We know what’s going on.”

Maciejewski had just restarted collision monitoring, for the first time since 2011, weeks before the 2020 event, which provided the evidence needed to spark action. Otherwise, the birds would’ve been swept up and thrown away. “No one would have known about it,” he says. Now, surveying city sidewalks and overhangs tells Bird Safe Philly where to focus its outreach, benefitting migratory and resident species.

Russell and Maciejewski bring the casualties to the Academy of Natural Sciences of Drexel University. There, they get a new life by contributing to avian research. “We are creating this long record of what’s happened,” says Jason Weckstein, the museum’s associate curator of ornithology. “Collections like ours are really critical to understanding change over time.”

The collection reveals the species most prone to collisions—including Ovenbirds, American Woodcock, and White-throated Sparrows—and the conditions that are deadliest. Beyond that, Weckstein and colleagues at other institutions use window-strike specimens to study avian parasites, migratory routes, and how climate change is affecting birds’ physiology.

Lights Out programs started in Chicago and spread to more than 40 cities. But they’re just one important step toward making windows safer for birds. Glass poses a significant risk year-round during the day, reflecting sky or lush landscaping that, to a bird, is indiscernible from the real thing. Making glass visible can be as simple as hanging cords or installing grids of dots that are no more than 2 inches apart. “You want to make sure that you're cutting down that reflectivity,” says Connie Sanchez, ���Ϲ���’s bird-friendly buildings coordinator. The treatments minimally obscure humans’ view but make a world of difference to birds. 

Bird Safe Philly is expanding its efforts beyond Lights Out with education and outreach to building owners, designers, and architects about incorporating bird-safe glass in construction plans. Long-term, they’d like to advocate for changed building codes or legislation to govern new structures.

Migrating birds, many traveling from the northern boreal forests to Central and South America, have a gargantuan task as they navigate challenges like habitat loss and inclement weather. But ours is easy, Sanchez says: Make windows safer and turn off the lights.

This story originally ran in the Spring 2022 issue as “Night Life.” To receive our print magazine, become a member by .