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Windows Pose Life Threatening Threat to Birds
From Animals In Print
The On-Line Newsletter

From 8 November 2004 Issue

Windows Pose Life Threatening Threat to Birds
Mary Beth Breckenridge

It's a stomach-turning sound to anyone who's seen or heard a bird fly into a window at full tilt. Birds can't distinguish glass from open air, and that lack of judgment can injure or kill them.

No one knows how many birds whack into windows each year, but researcher Daniel Klem Jr. estimates the U.S. death toll at 100 million to 1 billion. That's as much as 5 percent of the bird population after the breeding season, and he suspects the actual number is even higher.

``Almost every structure on this planet has a piece of glass in it,'' he said, and every one of those windows represents a potential hazard to birds.

Klem, an ornithologist at Muhlenberg College in Allentown, Pa., based his estimate on research indicating one to 10 birds are killed each year for each building in this country, on average. And that doesn't count all the birds that end up with sore noggins or battered beaks from their nonfatal run-ins.

The problem, Klem said, is that birds don't perceive glass as an object. They see the sky reflected in a window, or they spot habitat through another window beyond, and into the glass they go.

Bird watcher Bill Thompson III has seen as many as five birds a day killed against the windows of his house, which sits on a ridge in a rural area near Whipple in southeastern Ohio. His wife has a windowed studio that overlooks a brushy area, and especially during spring when the young birds are starting to fly, ``we get thunk, thunk, thunk, thunk,'' said Thompson, editor of the magazine Bird Watchers Digest and a director of the Ohio Ornithological Society.

About a quarter of North American bird species have been known to fly into windows under a variety of circumstances, Klem has written. Some are trying to outrun a predator. Some are migrating. Others are looking for food, water or shelter.

Most strikes happen in winter, he said, when birds visit feeders in large numbers and often run into windows on their way to or from feeding stations. The problem gets the most attention during spring and fall migrations, however, because window accidents and their victims are most noticeable then.

Mating season is a time for a less dangerous kind of bird strike, when a male bird -- often a cardinal or robin -- sees a reflection of itself and think it's competition, said Damon Greer, a wildlife biologist with the Ohio Department of Natural Resources' Division of Wildlife. The bird will peck at the glass persistently to try to get at the intruder, sometimes for weeks on end. The bird rarely suffers anything worse than the occasional bloodied bill, Greer said, but the humans on the other side of the window can be driven to distraction.

Klem has argued for changes in building design to reduce bird strikes, including angling first-floor windows downward so they reflect the ground instead of the sky. So far, he said, he's gotten little heed from the building industry.

That could be changing, though. Audubon magazine wrote in its March issue that Klem's work has influenced construction projects including a science building at Swarthmore College, which will have windows with dots of opaque glass to discourage bird strikes. And the New York City Audubon Society is campaigning for bird-friendly design in any buildings that rise on the World Trade Center site.

In the short term, however, challenges remain. Thompson, for example, tried to have windows installed at a downward angle on a construction project at his farm and discovered that doing so would void the manufacturer's warranty.

Avoid bird strikes

Bird experts offer other suggestions for preventing bird strikes, such as stretching netting over windows to cushion the blow or hanging objects just outside to break up the birds' view. None is foolproof, however, and homeowners often object if they obscure the view, block the sunlight or look unattractive.

Still, Thompson believes they're useful at least as short-term measures for times when bird strikes are prevalent, such as migration.

``There are some drawbacks to every single one of them,'' he said. ``... You have to balance utility with making them (windows) as safe as possible for birds.''

Return to Animals in Print 8 November 2004 Issue

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