Research Shows Turning Off Building Lights at Night Reduces Bird Collision Cases

A study based on decades of research found that turning off building lights at night can prevent migrating birds from colliding with structures.

Scientists discovered that when half the windows of a massive building in Chicago were darkened on nights when all the windows were illuminated, there were 11 times fewer bird collisions during spring migration and six times fewer collisions during fall migration.

Concerned Conservationist

David Willard, the Field Museum's retired collections manager, overheard an offhand remark about birds striking McCormick Place, North America's biggest convention center, approximately a mile south of the museum, in 1978.

"One morning, I went down to the building and saw three or four dead birds, some of which were already insect-infested. That sparked my curiosity. We began going more regularly and then every day to pinpoint the nights when the birds flew into the buildings.

"If I hadn't discovered anything the first day, I would not have gone back, and now here we are, 40 years later and 40,000 birds later."

Finding Dead Birds

Willard claimed he and his coworkers might come across no dead birds on some days but up to 200 on others. "Over the 40 years, that has happened maybe four times. So the number zero is far more prevalent than the number 200."

Willard gathered the dead birds and returned them to the museum, where he entered each one into a ledger and added them to the collection.

Willard didn't see a trend until he was 20 years old. The following day, fewer birds were on the ground on evenings when the lights were turned off at McCormick Place. So, in addition to gathering the birds, he collected data on which windows were lighted each night when the building's lighting patterns began to shift.

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Lighting Observations

Willard's specimens and lighting observations were combined with other data on variables that can have a role in bird death, such as weather records and radar data, by Benjamin Van Doren, a postdoctoral associate at the Cornell Lab of Ornithology and the paper's primary author.

"Our research gives the greatest evidence yet those building lights attract migrating birds, leading them to hit with windows and die," he added.

Creating Statistical Models

He and other researchers devised a statistical model that predicted that decreasing the number of illuminated windows might reduce collision counts by up to 11 times in the spring and six times in the autumn. Moreover, turning off half the lights at McCormick Place might cut bird death by 59% during migratory seasons.

"The sheer scale of the effects that building lights may have on birds that we found astounded me. It points to the tremendous prospect of lowering light pollution to preserve birds."

Birds and Building Lights

Birds have special abilities when it comes to exploration. Building lights can be perplexing to them, especially on gloomy evenings, causing them to circle in circles. Some people may collide with buildings if they see plants or trees reflected in the windows.

Over the last half-century, the United States has lost more than a quarter of its bird population, or around 3 billion birds.

"Buildings are killing birds all around North America and the world, and it adds up," said Doug Stotz, a senior conservation biologist at the Field Museum. I believe that this research will demonstrate why it is critical to turn off indoor illumination as well, particularly in Chicago, the country's worst city for migrating birds."

Van Doren thinks that the research will complement initiatives currently underway in Chicago, such as the Lights Out program, which urges owners and managers of tall buildings to turn off lights to prevent migratory disturbance and urges people to do the same.

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