As part of the "Lights Out Chicago" campaign, residents of tall buildings are asked to turn out their lights or draw their blinds after 11 p.m. during the migration season, which runs from late August through November.
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The recommendations apply to all buildings of 40 or more stories and to buildings of 20 or more stories that are isolated from other buildings.
Lights from tall buildings can disrupt birds' migratory paths, causing birds to circle buildings repeatedly, according to the Chicago Audubon Society. As a result, many of them die from exhaustion or after colliding with a building.
More than 250 bird species migrate through Chicago, with about 5 million individual birds making the trip each year. According to the Chicago Audubon Society, many of the birds killed at Loop buildings are small migrants from the tropics, like warblers, thrushes, tanagers and others.
For more information on the "Chicago Lights Out" program, visit ChicagoAudubon.org.