Philadelphia Turns Out the Lights to Save Migrating Birds

Building collisions kill as many as 1 billion birds annually.

Peregrine falcon outside Philadelphia's city hall.
Peregrine falcon outside Philadelphia's city hall.

George L. Armistead

Each year, as many as 1 billion birds are killed in the United States from collisions with glass windows and buildings. Philadelphia is the latest city encouraging buildings to turn out the lights at night to protect birds as they pass through by the millions during migration seasons.

Called Lights Out Philly, the voluntary program encourages property managers and tenants to shut off unnecessary external and internal lights during migration seasons. They’re asked to turn off lights between midnight and 6 a.m., particularly in a building’s upper floors, lobby, and atrium, and switch off or dim any external illumination. Peak migration seasons are April 1 through May 31 in spring and August 15 through November 15 in fall.

Philadelphia joins 33 other cities in national Lights Out programs, including Atlanta, Baltimore, Boston, New York, and Washington, D.C. The National Audubon Society created the first Lights Out program in 1999 in Chicago.

Bird/glass collisions are common for several reasons, Keith Russell, program manager of urban conservation at Audubon Mid-Atlantic, tells Treehugger.

“Artificial light at night (ALAN) can attract birds that migrate at night to buildings and ultimately cause them to collide with buildings and outdoor structures,” Russell says. “Reflective and transparent glass are also hard for birds to recognize as hard surfaces, and these artificial lights at night also allow the deceptive qualities of glass that often fool birds during the day to operate also at night.”

Because most birds migrate at night by navigating with the night sky, Russell says turning off lights between midnight and dawn helps minimize the effect of artificial light at night when most birds are traveling. 

A Dangerous Migration

Each year, tens of millions of birds pass through Philadelphia along a migration route known as the Atlantic Flyway between their wintering habitats and breeding habitats.

“These transients, which occur mainly during the spring and fall, are responsible for the peak in collision numbers that occur during those seasons,” Russell says.

During an Audubon monitoring study performed from 2008-2011 in downtown Philadelphia, researchers estimated that as many as 1,000 collisions occurred annually in the 3.5-square block area they were monitoring.

“But that area contained many buildings that were probably more prone to collisions than the average building in the downtown area,” Russell points out. “We have not collected enough data overall to be able to estimate the average number of collisions occurring per block each year for the downtown Philly area as a whole.”

But one massive event was heartbreaking and easy to count.

On Oct. 2, 2020, Philadelphia had its largest mass collision event in more than 70 years with an estimated 1,000 birds colliding with buildings in one 3.5-square block area in just one day.

“Paired with a perfect storm of weather and fog conditions, the bright city and building lights attracted and confused the migrating birds causing them to collide with building and outdoor structures,” Russell says.

This event triggered the formation of the Bird Safe Philly coalition, which includes Audubon Mid-Atlantic, the Academy of Natural Sciences of Drexel University, the Delaware Valley Ornithological Club and two local Audubon chapters—Valley Forge and Wyncote.

Bird Safe Philly is behind the Lights Out Philly initiative.

Ovenbirds and Warblers

The Academy of Natural Sciences began collecting birds that crashed into Philadelphia buildings in the 1890s. At that time, The Evening Bulletin noted “window kills” after the lighting of the city hall tower in 1896.

Nearly 100 species of birds are known to have died from collisions with buildings and other structures in Philadelphia, says Russell. Many other species are observed in the city and are also probably affected, he notes.

“Today the most common species to meet their demise by Philadelphia buildings are Ovenbirds, Common Yellowthroats, White-throated Sparrows, and Gray Catbirds. But, we are particularly concerned about species that are already facing population declines and an increased risk of extinction from climate change like Ovenbird and the Black-throated Blue Warbler,” Russell says.

“We are also concerned about less common species like the Yellow-breasted Chat and Connecticut Warbler which appear to be more prone to collisions based on our monitoring.”

Early participants in Philadelphia include BNY Mellon Center, Comcast Technology Center and Comcast Center, Jefferson Center, One South Broad, One Liberty Place, Two Liberty Place, and 1515 Market Street.

Even if you don't play a part in managing the lights of a big building, you can help birds avoid collisions by making glass surfaces visible and minimizing light at night. Smithsonian researchers found that that 44% of window-crash fatalities happen as homes and other buildings just one to three stories tall.

“Reduce the reflectivity and transparency of glass by covering it with dense patterns, making it appear opaque, or place physical barriers in front of the glass/window,” Russell says.

“Reduce the amount and intensity of artificial light at night, change the color of lighting to blue or green, shorten the duration lights are on, direct the lighting downward (or shield lighting).”

For more on preventing bird strikes at home, visit the American Bird Conservancy's comprehensive and helpful section on window collisions.