With our cities, humans have inadvertently created a landscape that is intrinsically peril­ous for migratory birds. Nocturnally migrating birds can be disoriented by light and become “trapped” by illuminated structures. Throughout modern history, “clouds of birds” have been observed fluttering around lit-up structures, such as lighthouses, bridges and skyscrapers, including these well-known landmarks:

• Statue of Liberty
• Washington Monument
•  Empire State Building

Trapped like moths at a porch light, the birds are vulnerable to colliding with the structures or even each other. Birds that don’t strike the building eventually become exhausted and take refuge in nearby trees or shrubs.

Once in the urban environment, birds often collide with windows, either because the glass is:

1.  transparent, and shows a potted plant inside, or
2. reflective, and mirrors the surrounding area.

Both types effectively mask the solid nature of glass, which the birds are unable to perceive as a barrier. As a result, window strikes are believed to be a major source of bird mortality. Some experts maintain that after habitat destruction, glass poses a greater threat to birds than any other human product or activity. A conservative estimate puts the number of birds killed annually in the U.S. by striking window at 100 million—one bird for every building.

Individual office buildings kill many more. Between April 1997 and May 2001, NYCAS volunteers found at the World Financial Center 720 dead or injured birds of 63 differ­ent species. Seventeen of those species are experiencing significant long-term population declines. These totals reflect only the birds actually found; the vast majority of casualties went undocumented. With just a handful of volunteers providing limited coverage, many more birds were swept up by cleaning staff or scavenged by predators (cats, rats, gulls, etc).

Two hundred twenty-five species—25% of all bird species in North America—have been documented as colliding with windows. This is not natural selection, which removes individuals that are least likely to survive and reproduce. Collisions affect both adult and juvenile birds, whether fit or unfit.

In Toronto, volunteers with the Fatal Light Awareness Program (FLAP) found 15,036 window-strike casualties between 1993 and 2000. FLAP calculates that some 10,000 birds are killed or injured each year in downtown Toronto alone.

Multiply these numbers by all the cities that lie between birds’ breeding grounds in north­ern Canada and their wintering grounds in Central or South America, and you have a sig­nificant source of mortality. What makes these deaths all the more regrettable is the fact that they could be prevented. Any measures to avert further mortality could save millions of birds and make a difference in species’ long-term survival.