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Each year, as many as one billion birds are killed in the US from collisions (相撞) with glass windows and buildings every year. Birds that crashed into Philadelphia buildings began to be collected in the 1890s. Nearly 100 species of birds are known to have died out from crashes with buildings and other structures in Philadelphia. Many other species are probably affected in the city.

Called Lights Out Philly, the voluntary program in Philadelphia encourages buildings to turn out or dim unnecessary external and internal lights between midnight and six o’clock early in the morning to protect birds as they pass through during migration seasons.

Bird migration seasons are from April l to May 31 in spring and from August 15 to November 15 in fall. Each year, millions of birds pass through Philadelphia along a migration route known as the Atlantic Flyway. Bird-glass crashes are very common for migrating birds, most of which travel at night. Glass is difficult for them to recognize as hard surfaces, and artificial light can fool them into crashing with buildings and outdoor structures. Turning off lights between midnight and sunrise helps minimize the effect of artificial light when most birds are migrating.

On Oct. 2, 2020, a stormy and foggy day, Philadelphia had its largest mass collision event in more than 70 years with an estimated 1,000 birds crashing with buildings in one 3.5-square block area in just one day. Paired with a terrible storm of weather and fog conditions, the bright city and building lights attracted and confused the migrating birds, causing them to crash with buildings and outdoor structures.

Even if you don’t play a part in managing the lights of a big building, you can help birds avoid crashes by making the glass opaque to reduce the amount and intensity of artificial light at night, changing the color of lighting to blue or green, shortening the duration lights are on, directing the lighting downward or screening lighting.