Birds & Conservation >

How many birds are killed each year in collisions with windows?

The question seems easy but the answer is we just don’t know. Even scientists who have studied this issue in depth vary widely in their own estimates of bird mortality due to window collisions. But while they may continue to debate the numbers, most agree that bird collisions are a source of potentially significant and indiscriminate mortality for birds, many of which are already in serious decline due to other pressures. Unlike some of the other major threats to birds, such as habitat loss and pesticide use, this is something that citizens can do something about.

Birds have been migrating for millennia—why don’t they learn to avoid buildings?

Birds collide with windows in the daytime when they see the outdoors reflected in the glass and think they have a clear flight path. Most migrants fly at night, and the artificial lights in tall buildings confuse them and cause them either to crash into the structure or circle it repeatedly until falling to the ground in exhaustion. Tall lighted buildings are especially lethal in fog, low clouds and rain.

As the human population grows, we build more and more structures, and the areas that are attractive to humans—riverbanks, coasts, shorelines—are birds’ traditional migratory pathways. Our built environment is proving to be more and more of a challenge to migrating birds.

If buildings are so dangerous, why don’t we see piles of dead birds on the sidewalk each day?

Many of the birds that strike windows are killed outright and fall to the ground where predators, such as gulls, crows, cats and other scavengers quickly carry them off. Those that survive an impact may be too injured to fly and find some place to hide as the city wakes up. Those that retain flight ability may be so frightened by the noise and activity of a city in daytime that they fly up and collide with a building again.

© Linda Krueger

What kinds of birds collide with buildings?

Bird mortality from window strikes has been recorded in more than half the bird species in the United States. Many of our favorite birds are included on this list, including ruby-throated hummingbirds, song sparrows, hermit thrushes, many kinds of warblers, indigo buntings, black-capped chickadees and gray catbirds.

Won’t a darkened city be unsafe?

Not at all. Lights Out cities don’t go completely dark, by any means. Lights Out focuses on dimming or extinguishing extraneous lights coming from buildings, particularly in the upper stories. This includes the bright, decorative lighting that defines the building top, as well as interior office lights that aren’t being used. Street-level lights, though preferably down-shielded, and airplane warning lights are not affected.

While many buildings may choose to alter their lighting practices year round, Lights Out for birds is technically in effect during key migration periods late at night. This usually means about 10 weeks in spring and10 more in the fall, between the hours of midnight and daylight.

How do we know that dimming or turning off lights can help?

Turning off unnecessary lights in buildings has been shown to reduce the number of birds attracted to or confused by illumination. Since Chicago buildings began dimming or turning off lights, many more birds are navigating through the city successfully. In fact, at one building where records have been kept for many years, mortality decreased by 80 percent when lights were turned off. Toronto, New York and Detroit are also Lights Out cities and are compiling data on bird mortality.

What do building owners get out of participating?

A Lights Out program leads to real energy savings, which translate to cost savings. Participating buildings save birds, save money and save energy while reducing carbon emissions. Many buildings are also interested in certification through the LEED system—a “green” rating system for buildings, indicating Leadership in Energy and Environmental Design. Building owners, managers, employees and tenants also take pride in their participation in Lights Out.

How many birds are killed each year in St. Paul and Minneapolis?

We don’t yet have data to use to estimate the size of the problem in the Twin Cities, but trained volunteers will survey around downtown buildings for the first time this spring and fall during peak migration to collect fallen birds. Live birds can be released if they are found stunned, while injured birds will be taken to the Wildlife Rehabilitation Center in Roseville. Dead birds will be collected at the Bell Museum and a data base will be developed. Based on observations here and in other cities, there is no doubt that lighted buildings in the Twin Cities do kill birds.

Why should we care if some birds are lost on migration in this way?

As stewards of the environment everyone should be concerned about conserving birds. Birds perform many useful functions, from pollination to seed dispersal to insect control.

In spring their return signals the renewal of the seasons just as their fall departure precedes the changeover to winter. Their songs and daily activity bring joy to nearly everyone. We can save millions of birds by turning off the lights in tall buildings at night. Migration is such an arduous business for birds, we should do everything we can to make it easier for them.

How can I help save birds?

You can help in two important ways. One is to make your windows at home safe for birds. Another way is to volunteer to help survey downtown buildings during migration for fallen birds— contact Audubon Minnesota.