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Spring 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

May 10, 2011

Bright buildings are hazardous to migrating birds

At 5:30 a.m., Anne Lewis and Elizabeth Shope begin searching the plazas that front about a dozen buildings at the eastern end of downtown Washington.

They are are looking for dead or injured migratory birds, casualties of modern architecture.

Lewis, an architect, is conducting a survey of fallen birds for Lights Out D.C., a project of City Wildlife, a nonprofit organization that she heads. Like similar groups in other urban areas, City Wildlife wants building operators to turn off their lights at night.

Lewis first stops at the Thurgood Marshall Federal Judiciary Building, which has several attributes that can put a bird on a collision course: The front of the building has converging planes that "funnel birds into the glass at the entrance," Lewis says. Massive foliage inside the building can attract a bird looking for a safe place to perch. "The three major problems here are transparency, reflectiveness and light," she says.

Since night-migrating birds use light signals (stars) to help them navigate, migrants become confused by, and even drawn toward, brightly lit buildings. "Look," Lewis says, pointing at the building, "every single light is on."

Of course, it's not the light that kills them. It's the glass.

Birds have problems detecting glass, which can be either too transparent, inviting them to fly through it, or too reflective, presenting birds with a deadly illusion of trees and sky.

Many birds are killed instantly by the impact, but some survive. Lewis recently rescued a stunned ovenbird, which she held in a protective cage until it regained its senses. She released it into woodland habitat near a water source. Less fortunate was a whippoorwill that perished after attempting to fly through the Hart Senate Office Building.

On L Street, beneath the mirrored skywalk of the D.C. Convention Center, traffic has squashed a gray catbird into a pancake of charcoal feathers. A flattened sparrow lies nearby. If the birds had fallen onto the sidewalk instead of the street, early-morning maintenance workers would probably have disposed of them.

That's one reason why Lewis, Shope and eight other volunteers get an early start. But, Lewis adds, "we also have to get there before the crows do." At dawn, crows run their own surveys, snatching up collision victims for breakfast.

SOURCES: USDA Forest Service; Jim Monsma, www.citywildlife.org

Common Yellowthroat; Bird mortality from anthropogenic causes; Thurgood Marshall Federal Judiciary Building

The clear glass facade of the Thurgood Marshall Federal Judiciary Building is the site
of numerous bird impacts.

To reduce collisions, architects can choose to use glass covered with patterned or ultraviolet reflective coatings. (Birds can see UV light but humans can't, so the pattern
is almost invisible to humans.)

Turning lights off at night would greatly reduce bird deaths.