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How researchers test bird-friendly glass designs

Researchers at Foreman’s Branch Bird Observatory in Chestertown, Maryland, use this tunnel to assess the designs of glass windows without injuring their feathered test subjects. Photo by Washington College

Window collisions are one of the single-biggest causes of death for birds, accounting for up to 1 billion fatalities a year in the United States alone. Luckily, demand for bird-friendly glass is on the rise thanks to growing awareness of the issue and new bird-safe building policies in places like New York City. To meet this demand, American Bird Conservancy (ABC) is expanding its capacity to test bird-friendly glass designs.

Last fall, North America’s second-ever bird-friendly glass testing tunnel debuted at Foreman’s Branch Bird Observatory in Chestertown, Maryland. The new tunnel, which is jointly run by Washington College and ABC, more than doubles the number of glass designs that can be tested by ABC for bird-friendliness each year. As the first testing tunnel located on a campus, the new tunnel also gives college students a hands-on look at how conservation research can be put into action to save birds’ lives.  

Tunnel technician Meghan McHenry of Washington College holds a pane of glass to be tested in the tunnel. Photo courtesy Washington College

ABC and the Powdermill Avian Research Center first began testing glass with a tunnel at a bird-banding station in Rector, Pennsylvania, in 2010, where researchers developed a rigorous process. In each trial, a bird is caught locally by licensed bird banders, then released into one end of the 24-foot-long tunnel. The bird flies toward the light at the other end, where a test pane and a clear glass pane placed side by side present a choice. ABC assigns the glass a “Material Threat Factor” score based on the number of trials in which a bird flies toward the test pane (each sample is tested 80 to 100 times). The more often birds avoid the test pane, the more likely they can see the bird-safe alteration and avoid the glass in the wild. Tested birds safely bounce off a mist net before reaching the glass, and each bird is released back into the wild after a single test flight.

During the fall migration season last year, Washington College employed a recent graduate as a tunnel technician to lead testing efforts. Under her guidance, the college ran more than 2,500 test flights and approved 10 new glass designs after testing samples from manufacturers in the U.S., U.K., Brazil, Germany, Turkey, and South Korea. This spring and summer, a combined total of more than 20 glass samples will be tested at the Pennsylvania and Maryland tunnel locations.

This story is by Rachel Fritts, writer/editor at American Bird Conservancy. The article was published in the July/August 2022 issue of BirdWatching.


Read about products that prevent birds from hitting windows

Watch a video showing a worker using the test tunnel

Downloadable resources for preventing glass collisions

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