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Frequently Asked Questions

Bird in hand

When do birds migrate through the Chicago area?

For the majority of bird species, spring migration begins in mid March and can continue into early June. (As they leave their winter homes, birds need to time their migration according to food sources becoming available along their path northward.) For the majority of bird species, fall migration begins in mid August and can continue into early November. (There are some birds that begin their journey south as early as the month of July!)

What types of birds collide with windows in Chicago?

Collision victims range from birds as big as geese and hawks to as small as hummingbirds and warblers. Chicago Bird Collision Monitors have recovered birds from over 150 different species.

What birds are most frequently found?

Why are lights hazardous to migrating birds?

Birds migrating at night are fatally attracted to the bright lights on top of multi-story buildings. It is thought that lights confuse the navigation systems of birds causing them to circle buildings repeatedly until in their disoriented state, they strike the building or die of exhaustion. Brightly lit lobbies tempt birds to fly towards attractive indoor plantings and fountains. Birds will think they can fly through or into any buildings areas with large areas of transparent glass. Birds will fly towards false images of trees, plants, or sky that they see in the reflective glass surfaces of buildings. Learn more about light reduction efforts. (See: Lights Out for more information.)

Why do birds strike windows?

Birds collide with every size and kind of glass window, door, or lobby. Reflective glass windows present deceptive images of trees, water, or sky that a bird may fly towards. Transparent glass windows present an invisible barrier that birds will try to pass through to reach another area or to get to attractive lighting, plantings, fountains, or shelter in a building's interior. Learn about how to prevent window strikes. (See: Prevent Window Strikes for more information.)

Why do we care if migratory birds are killed by collisions?

Migratory birds are a critical part of the balance of nature that affects us all. Plants and animals above and below them on the food chain depend on birds for their survival. Birds pollinate plants, disperse seeds, and control insects and other pests as well as being part of the natural world we all need and enjoy. Many of the world's bird populations are in serious decline, facing ever-increasing threats on all fronts from loss of habitat, to the hazards of man-made structures, to air, soil and water pollution. It is critical that we do what we can to minimize or eliminate these dangers whenever possible. No doubt we will continue to erect tall buildings, communications towers, and wind farms, but we can do so responsibly, using bird-safe materials and lighting, and appropriate siting, so as to minimize harm to birds.

Are birds that hit windows just the dumb ones?

Avoiding windows is not a matter of intelligence but experience and learning. Even humans walk into glass surfaces until they learn to reference these invisible barriers. The migratory birds that strike windows normally live in rain forests, open prairies, woodlands, wetlands and other natural areas where they have not experienced man-made structures and the dangers they present. Birds have been migrating along Lake Michigan for thousands and thousands of years. Giant skyscrapers with lighting and massive amounts of glass appeared in just the last hundred years. Not nearly long enough for birds to have evolved the natural instincts to avoid these hazards.

How many birds are recovered each year?

The number of dead and injured birds found in Chicago varies from year to year and season to season. Weather patterns and conditions can affect/influence/determine the number of birds that are found on certain days. In recent years, thousands of birds have been recovered during migration seasons. We know that this is only a portion of the birds that are injured since many fall onto inaccessible locations (roofs, awnings, ledges, gratings, etc.) where rescue is impossible. Others are eaten by predators and swept up before volunteers reach them. Help us recover more birds by joining our efforts (See: Volunteer for more information.) or contacting us (See: Contact Us for more information.) when you find a bird in harm's way!

Which building kills the most birds?

Any structure with hazardous lighting, transparent or reflective glass and attractive interior or exterior landscaping near windows or lobbies, be it a skyscraper or single story, can pose a danger to birds that find themselves in that location. Areas for bird strikes vary from day to day and season to season. The odds of birds colliding increases when there is attractive landscaping or habitat that invites birds into proximity with buildings that have high amounts or reflective or transparent glass.

What can be done to prevent bird strikes?

If you are an architect, commercial building owner, manager or tenant, look at our Examples of Bird-safe Buildings page to see examples of good lighting and building designs. Find ways to mitigate dangers at trouble areas. If you want to make your private residence safer for birds, look at our Prevent Window Strikes information for permanent and temporary ways to reduce hazards for birds. Contact CBCM to discuss options for making your building bird-safe.

If a bird flies away when I attempt to rescue it, does that mean the bird will be OK?

Not necessarily. Nature provides animals with a powerful instinct to flee predators. Even a seriously injured bird will do all it can to escape capture. In most cases, if you suspect a bird has sustained an injury, it's best to continue efforts to capture and contain it, without unduly stressing the bird. The bird then can be assessed and treated as needed by a wildlife specialist.

Can a bird breathe in a closed paper box or bag?

Yes, sufficient air is available in a cardboard box with a lid or a paper bag (unwaxed/uncoated) that is clipped shut at the top. These are not air-tight containers. However, sealed plastic bags or other plastic containers are not appropriate and could suffocate a bird. Birds are quieter and less stressed inside a closed paper box or bag where it is dark and away from human contact and noise.

What happens to the birds found downtown?

The majority of the collision-injured birds recover if they are retrieved before being attacked by gulls and crows, stepped on by pedestrians, run over by cars or swept up by cleaners as they lay vulnerable on the city sidewalks and streets. Depending on the severity of their injury, birds may need hours or days to recover. Optimally, birds should have minimal invasive treatment and time in captivity before they are released into safe habitat to continue their migration. Unfortunately, some birds sustain injuries too serious to survive.

Do the injured birds survive?

Injured birds are taken to either Willowbrook Wildlife Center or Fox Valley Wildlife Center (See: Wildlife Centers for more information.) to be evaluated by wildlife specialists and provided appropriate treatment.

Dead birds, and any that don't survive treatment, are taken to Chicago's Field Museum of Natural History, where they become part of the museum's Bird Division display, research, and educational collections. Find out more.





Chicago Bird Collision Monitors (CBCM) is an all volunteer bird conservation project that operates under the auspices of
the Chicago Audubon Society.


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