Bird-Friendly Design - Part Two: Problems with Glass
by Christine Sheppard
Glass can be perceived differently depending on a number of factors, including how it is fabricated, the angle at which it is viewed, and the difference between exterior and interior light levels.
Combinations of these factors can cause it to look like a mirror or dark passageway, or to be completely invisible. Humans do not actually "see" most glass, but are cued by context such as mullions, roofs or doors.
Birds, however, do not perceive right angles and other architectural signals as indicators of obstacles or artificial environments.
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Viewed from outside, transparent glass on buildings is often highly reflective. Almost every type of architectural glass, under the right conditions, reflects the sky, clouds, or nearby habitat familiar and attractive to birds. When birds try to fly to the reflected habitat, they hit the glass.
Reflected vegetation is the most dangerous, but birds also attempt to fly past reflected buildings or through reflected passageways.
Birds also strike transparent windows as they attempt to access potential perches, plants, food or water sources, and other lures seen through the glass.
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The glass-walled towers of the Time Warner Center, in New York, New York, can appear to birds as just another piece of the sky.
Photo: Christine Sheppard/ ABC
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Glass of this Washington, DC atrium poses a double hazard, drawing birds to plants inside, as well as reflecting sky above.
Photo: Courtesy American Bird Conservancy (ABC)
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