Every Sept. 11, beams of light rise more than four miles into the night sky from the National 9/11 Memorial & Museum in Lower Manhattan to honor the nearly 3,000 lives lost in America’s most devastating terrorist attacks. The glowing columns elegantly trace the outlines of the twin towers. But they also beckon thousands of migrating birds into the city’s skyscraper canyons, where they can become disoriented and crash headlong into buildings.

Since 2005 , thanks to efforts by New York City Audubon and the officials and producers of the tribute, this potential danger has largely been eliminated. This success offers lessons for other light-polluted cities across the country. Nationwide, nearly 600 million birds die every year in collisions with buildings, according to the Smithsonian Migratory Bird Center.

Early September is the peak time for the fall migration in New York C ity. Hundreds of millions of birds pour down from Canada’s boreal forests, winging their way south along the Atlantic Coast toward tropical destinations in the Caribbean, Mexico and Central and South America. These birds fly at night, availing themselves of the typically calmer nocturnal atmosphere to fly more efficiently and to minimize a chance encounter with a hawk or a falcon. They navigate in part by the stars but can become confused by the artificial light from urban areas.