Philadelphia lies within a bird migration pathway called the Atlantic Flyway. Each year, tens of million birds pass through Philadelphia during the spring and fall migration. Unfortunately, many are killed when they fly into buildings, confused by artificial lights at night or by reflective or transparent glass surfaces.

On October 2, 2020, a mass collision event occurred where thousands of birds were killed in Center City as a result of striking buildings.  This event prompted the formation of Bird Safe Philly.  Bird Safe Philly, or BSP, is a partnership designed to help protect birds in the Philadelphia area from collisions with buildings and other structures.  Its aim is to develop awareness within the community and implement solutions to prevent collisions.

Bird Safe Philly Activities

Collision Monitoring

Bird Safe Philly’s monitoring efforts involve volunteers gathering collision monitoring data from certain locations within the city.  This data can be used to determine which species collide with buildings, the number of collisions, as well as the times of year and time of day that these collisions occur.  Between 2008 and 2023, 120 species were known to have collided with buildings in Center City.  The data collected by volunteers in the Independence National Historic Park and 19th Street areas reported 877 and 643 collisions in 2021 and 2022, respectively.  The preliminary 2023 data (collected in November 2023) reports 519 collisions, the top ten of which were:

SpeciesNumber of Collisions
White-throated Sparrow92
Common Yellowthroat33
Black-and-white Warbler25
Song Sparrow21
Hermit Thrush19
Northern Parula19
Gray Catbird17
Dark-eyed Junco16
Yellow-bellied Sapsucker14

It is worth noting that the data collected by the volunteers represent a fraction of the total collisions in the city that are unfound/unrecorded.

The primary causes of collisions with buildings are reflections and artificial lighting.  Birds can mistake reflections they see on windows and glass surfaces for real scenes, and can mistake transparent glass surfaces for clear passages to fly through.  Birds are particularly sensitive to light when migrating at night, and artificial lights can disorient them, causing them to collide with buildings.

In addition, recent data collected from weather radar scans has revealed that skyglow due to artificial light is a top predictor of migration stopover density.  Stopover sites are locations where birds pause to rest, refuel and seek shelter.  Urban and suburban areas pose a challenge as there are fewer suitable options for stopover sites, the presence of non-native plants at stopover sites, and stressors associated with urbanization.

Lights Out Philly

Lights Out Philly was launched in 2021, as an effort to reduce bird collisions.  It is a voluntary program where businesses and residents turn off lights at night during spring and fall migration seasons.  The collision monitoring data mentioned previously suggests this effort is saving lives of migrating birds.


Through the Collision Monitoring and Lights Out Philly programs, Bird Safe Philly has made the Philadelphia are safer for migrating birds, and through advocacy and education, continues to raise awareness on the importance of protecting birds from building collisions.

Author: Judy Cadmus