Lights Out Frequently Asked Questions

Why are tall buildings a trap for migrant birds?
Lighted structures are dangerous to migrants. Some buildings intrude into their flying space, such as skyscrapers or communication towers. For reasons that are not well understood, birds are attracted to lights on these structures, circling them until exhausted and unfit for the remainder of their migratory journey. These birds may crash into buildings or windows, or become easy prey for crows, hawks and gulls at sunrise.

Why are bird kills so much bigger on certain nights?
The weather plays a big role in how many birds are killed on any one night. On overcast nights, birds fly lower and are more likely to be trapped by lights. Favorable winds (in Chicago, south in the spring and north in the fall) produce greater numbers of migrants, hence more deaths.

Do other lights cause problems for birds?
Another danger comes from shorter lighted buildings along the lakefront. Migrants are often caught over Lake Michigan as night ends, and head for shore and the nearest shelter. Research proves that extinguishing lighted windows in these buildings decreases mortality by 80 percent.

Also, some buildings have lighted atria with extensive glass windows, sometimes with vegetation indoors. Birds do not perceive the glass and will crash into these windows.

How big is the problem?
At Chicago's Field Museum, studies have been done using birds collected at a lakeside building and a downtown skyscraper. One building was found to have killed over 1,000 birds a year when lights were not extinguished. Museum biologists estimate that over ten thousand birds would be killed in Chicago each year, if lights were not extinguished.

Why are they in Chicago?
Radar studies show that birds migrate in a broad front across the Midwest, in what is called the Mississippi flyway. Many birds use the skies over Chicago.