On Oct. 2, 2020, thousands of migratory birds died after colliding with buildings in Center City Philadelphia. The event inspired the creation of Bird Safe Philly, a coalition of groups that monitor bird strikes in the region, educate the public, and promote a “lights out” campaign and exterior glass treatments.

Building collisions cause about one billion bird deaths in the U.S. each year, says Jason Weckstein, associate curator of Ornithology at the Academy and associate professor of the Department for Biodiversity, Earth and Environmental Science in the College of Arts and Sciences. Buildings are the second-biggest killer of wild birds, after feral and free-range domestic cats, he adds.

An estimated 1,000 collisions with buildings and windows can occur in just one four-square-block area in downtown Philly each year.

Bird Safe Philly is a partnership between Delaware Valley Ornithological Club, Audubon Mid-Atlantic, Valley Forge Audubon Society, Wyncote Audubon Society and the Academy.

They’re promoting a Lights Out Philly campaign to urge building owners and managers to extinguish unnecessary artificial lights during spring and fall migratory seasons. Pockets of data gathered in several cities that maintain Lights Out programs demonstrate that the intervention can reduce bird deaths from building collisions by as much as 80%.

“We don’t know why, but some birds are attracted to light,” Weckstein says. “It could be because birds that migrate at night actually use the stars for navigation.”

Constellations serve as a compass for migrating birds, Weckstein says, and glass surfaces in illuminated skylines might scramble their calibrations.

Now in its third year, Lights Out Philly has gained support from a growing number of building owners and managers, including Comcast Spectacor, the Pennsylvania Convention Center Authority and Brandywine Realty Trust.

Bird Safe Philly also promotes the installation of treated or patterned glass, motion-sensitive lighting, shades and other measures that individual residents as well as commercial builders and property managers can take to make buildings more bird-friendly year-round.

Nature lovers can also contribute to a monitoring program the partnership has established to document and tally bird deaths and injuries through the iNaturalist app.