Killer Windows

Killer Windows Photo Credit: Clipart.com

In autumn, a lot of birds begin migrating to their winter homes. In this Science Update, you'll hear why turning off the lights in city skyscrapers can help birds make the journey safely.


Why bright lights are bad for birds. I'm Bob Hirshon and this is Science Update.

In Chicago, the McCormick Place Convention Center hosts trade shows and exhibitions. But for the past two years, it's also been the site of a scientific study. Doug Stotz is a conservation ecologist at Chicago's Field Museum. He and his colleagues have been counting the birds that kill themselves by flying into the building's huge glass windows.

Every day during migration season, they count the birds on the ground outside the center and note which windows they crashed into. Stotz says bright windows seem to be much more dangerous than dark ones.


When the windows are not lit up, we found many, many fewer birds hitting the building than when the windows are lit up. And the reduction in numbers was at least 80 percent.

Stotz says that in a year, more than a thousand birds hit just this one building—suggesting that hundreds of millions of birds in the U.S. die this way.


Anyplace where there are large buildings, there are almost certainly birds hitting them and dying during migration.

He says the study lends support to what many cities, including Chicago, are thinking of doing: shutting off the lights at night so birds can migrate safely. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Although this scientific study is relatively new, Field Museum scientists have been scooping up birds in front of McCormick Place since 1978. Over 30,000 birds have crashed into that building in that time period, including several species of sparrows, thrushes, and warblers. And McCormick Place isn't even very tall, as city buildings go.

For a long time, the researchers assumed that all those crashes were inevitable. But several years ago, while the building was being renovated, Stotz's colleague, Dave Willard, noticed that he found fewer birds when the building's lights had been shut off the night before. That's what led to this study.

Scientists don't know for sure why the birds fly into the buildings, but Stotz says it's probably because the bright lights interfere with their navigation system. Most birds that migrate by night use the stars as a compass. When they fly over a city, the lights from the buildings can overwhelm the starlight and send them off course—in some cases, a collision course with the building itself.

As a result of studies like these, some building managers have volunteered to shut off their ornamental lights at night during migration season. Examples in Chicago include the Sears Tower, the 100-story John Hancock Center, and the Wrigley Building. Other buildings in other cities have followed suit.

Unfortunately, some buildings, including the McCormick Center, leave their lights on for security reasons, not decorative purposes. And of course, some high-rise buildings are residential, not commercial, which means the lights stay on until the tenants go to bed. Because of situations like these, it's unlikely that the conflicting needs of migrating birds and human city-dwellers will ever be completely resolved.

Now try and answer these questions:

  1. Why do some birds fly into buildings at night?
  2. What kind of birds are most at risk?
  3. Do you think building managers should be asked to turn off their lights at night? Under what circumstances? Do you think this should be voluntary, or regulated by law? Give reasons for your argument.
  4. What other human activities or structures have affected birds? Can their impact be reduced? How? What are some obstacles that might block potential changes?

For Educators

Chicago's Bird's Eye View of the Migratory Bird Route has information on the Lights Out program inspired by this study, area migratory birds, and more.

The Fatal Light Awareness Program, or FLAP, is a Toronto-based organization dedicated to this issue.

The Migration Website, from BirdWatch Ireland, has detailed notes on the hows and whys of bird migration.

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