Each year tens of millions of birds pass through Philadelphia in spring and fall while migrating between their breeding and wintering grounds. Many never complete their epic journey because they are killed when they fly into buildings, confused by the artificial lights and glass. 

A mass collision of thousands of birds in Center City on Oct. 2, 2020 prompted the formation of Bird Safe Philly to advocate for measures that would reduce the number of collisions, and in April 2021 Philadelphia joined the national Lights Out initiative. Since then, more than 100 commercial, residential and municipal participants in the Philadelphia region have joined in turning off lights at night to help prevent bird collisions. 

So how are we doing? 

While still in the early stages and with limited data, Lights Out Philly has already begun to see the positive effects of turning the lights off. At one monitored building where artificial light has been reduced the most (Atrium building in the courtyard of the BNY Mellon Center, 1735 Market St.) fall collisions have declined by 70% since 2020. Additional years of monitoring will be helpful in confirming the result, taking into consideration weather patterns, the size of bird populations, and other factors. However, long-term monitoring and data analysis in Chicago has verified that Lights Out is working to reduce collisions in that city. 

What is Bird Safe Philly? 

Bird Safe Philly was formed in 2020 by the Academy of Natural Sciences of Drexel University, Delaware Valley Ornithological Club, and National Audubon Society — Audubon Mid-Atlantic, Wyncote Audubon and Valley Forge Audubon. Bird Safe Philly — in collaboration with the City of Philadelphia Office of Sustainability, BOMA Philadelphia, and Building Industry Association of Philadelphia — initiated Philadelphia’s first Lights Out program in April 2021 as a primary way of preventing bird collisions caused by artificial light at night. Bird Safe Philly volunteers monitor certain downtown areas for dead and injured birds that have collided with buildings and collect data about collisions throughout the region through the popular iNaturalist website and app. Dead birds are added to the Academy’s Ornithology Collection where they can be utilized for research, and injured birds are taken to rehab. 

Why is Philadelphia important to migratory birds? 

Over 250 species of birds occur in Philadelphia annually, and 70% of these are migratory species. Scientific studies indicate the number of migrants that occur annually could exceed 50 million individuals. 

What dangers do migratory birds face when migrating through Philadelphia? 

One of the biggest threats that birds face, especially during migration, is collisions with buildings, transit shelters, glass walls and other built structures. These collisions are caused mainly by glass and/or by artificial light at night, and they are estimated to now kill 365 million to one billion birds annually in the U.S. and 16 to 42 million annually in Canada. 

What impacts are these collisions having on birds? 

Bird collisions are now considered a major conservation issue affecting birds throughout the world and one that has contributed to the loss of 3 billion birds in North America (about 30% of North America’s birds) since 1970. Some species are more susceptible to collisions than others, and many declining species like the Golden-winged Warbler and American Woodcock are highly susceptible to collisions. 

When do these collisions occur? 

Birds collide with structures throughout the year, but in urban areas the largest number of collisions typically occur during the spring and fall when bird migration peaks. Collisions can also occur any time of the day or night, but collisions involving actively migrating birds tend to peak from late at night until just after dawn. 

Which species are affected by collisions? 

As of 2023, 284 species of birds have been documented colliding with buildings in the U.S. and 119 species have been documented colliding with buildings in Philadelphia since 2008. Warblers (30 species and 48% of all individuals) and new world sparrows (nine species and 21% of all individuals) make up the largest percentages of the birds that have been documented colliding with buildings in downtown Philadelphia since 2008.  

What types of human structures do birds collide with in Philadelphia? 

Birds collide with structures of all types, heights, configurations and locations in and around Philadelphia. But collisions occur mainly at structures with large amounts of glass and/or artificial light at night, regardless of their height. In fact, 99% of all bird collisions in the U.S. occur on residential homes one to three stories tall and low-rise buildings four to 11 stories high. Less than 1% of collisions occur at high-rise buildings. This is because residences and low rises are much more numerous than high rises. But collisions at high rises get more notoriety because they are more visible and easier to document than collisions at homes and low rises, and because high rises can experience mass collisions involving hundreds or thousands of birds more easily than shorter buildings. 

How can collisions be prevented? 

Collisions can be prevented by reducing or eliminating artificial light at night and by placing patterns or physical barriers on or in front of windows and other types of collision prone glass surfaces to discourage birds from trying to fly through them.  

What has been done to prevent collisions from occurring in Philadelphia? 

Since 2008, Audubon Mid-Atlantic has worked to bring awareness to the bird collision problem in Philadelphia through education, monitoring, research and advocacy. Audubon has also worked with Temple University, the University of Pennsylvania, the City View Condo, John Heinz National Wildlife Refuge, and others to reduce collisions caused by glass. For much of this work Audubon collaborated with the Academy of Natural Sciences and (previously) the Philadelphia Zoo. Audubon also constructed the Discovery Center (2018) and John James Audubon Center (2019) to be collision-free buildings. And the Academy continues to offer exhibitions and programs to increase awareness of the issue. With the initiation of Lights Out Philly in 2021, the effects that artificial light at night can have on migrants began to be addressed for the first time.  

While Lights Out Philly can help reduce bird collisions caused by artificial light at night, Lights Out cannot prevent collisions caused by glass and other reflective or transparent surfaces that continue to occur during the day. The proliferation of new buildings in and around Philadelphia with mostly glass facades will only increase the number of bird collision deaths that are being caused mainly by glass.