Who turned off the skyline, and why? Philadelphia has joined a multi-city effort to help the millions of northeastern land birds that migrate in the spring and fall. Because 80 percent of these birds migrate at night orienting themselves by the stars, brightly lit tall buildings can be deadly. Confused birds frequently fly toward the lights and crash into reflective windows. Lights Out Philly was inspired by the city’s largest mass-collision event in 70 years reported last October. A heavy migratory flight combined with a low ceiling of clouds resulted in the death of many hundreds of birds.

The Guardian recently reported that “[s]cientists estimate between 365 million and 1 billion birds are killed by collisions with buildings or other outdoor structures in the U.S. every year and those crashes are taking a toll on some species.” Among those species are birds regularly found in Philadelphia, including “common yellowthroats, white-throated sparrows, gray catbirds and ovenbirds.”

Lights Out Philly runs from April 1 through May 31, and from August 15 to November 15. Property managers and tenants are asked to voluntarily switch off lights between midnight and 6 a.m., especially in a building’s upper levels, lobbies and atriums. Nearly 20 buildings have joined the effort so far. The National Audubon Society, along with partners, established the first Lights Out program in 1999 in Chicago. Philadelphia joins 33 other cities, including New York, Boston, Atlanta, and Washington D.C.