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1,000 birds crashed into Philadelphia buildings overnight. No one knows why

Birds commonly fly into the sides of buildings, but design changes can help.

1,000 birds crashed into Philadelphia buildings overnight. No one knows why
[Photos: dibrova/iStock, Nice_Kim/iStock, neil bowman/iStock]

On a single day, for reasons that can’t be fully explained, more than 1,000 birds crashed into buildings in Philadelphia and fell to their deaths. The blame falls at least partly on the buildings themselves, and the mass death event highlights a widespread problem with the way buildings are designed and built.

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Overnight on October 2, between 1,000 and 1,500 birds hit buildings in just a three-and-a-half-block radius. According to an article in the Philadelphia Inquirer, the number was far higher than on a typical night, and no one can explain exactly why.

According to a local Audubon Society volunteer quoted by the Inquirer, about 30 birds will have fatal collisions in this area on a typical day. Why this number suddenly jumped to more than 1,000 is a mystery.

Though the abnormally high number of deaths is shocking, it’s only a spike in what is an epidemic of deadly avian-architecture collisions. Birds commonly fly into the sides of buildings, as reflective surfaces and clear windows can appear as distant trees or clear paths of sky. Researchers estimate that collisions with buildings cause between 100 million and 1 billion bird deaths in the U.S. every year, and they add that most deaths are associated with buildings in the 4- to 11-story range. Most deaths at taller buildings, where reflective surfaces are the primary cause, tend to occur during migration periods. Glass facades, which started being developed in the mid-20th century, remain common in mid- and high-rise buildings.

Some birds are now on their fall migration from the cooling northern hemisphere to more tropical locations in Central and South America. John Rowden, senior director of bird-friendly communities at the National Audubon Society, says some birds migrate at night, using the moon and stars to guide their flights, which likely explains the high number of casualties. The high number of deaths seen in Philadelphia is rare, but not unprecedented, according to Rowden.

“We’re in the thick of migration right now,” Rowden says. “There’s adult birds that are coming back from their breeding grounds, but there’s also a whole ton of baby birds, brand new birds that have never navigated the built environment before and are naive to what that presents to them.”

Cloud cover may have caused the birds to fly lower than they usually would, and city lights can distort their sense of direction. The night-lit and reflective urban core of Philadelphia may have put them on a direct and deadly path into the sides of the city’s buildings. Like New York, Philadelphia is on the fall migration path of many birds.

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It’s a problem even Congress is trying to address. Included as an amendment in a recently passed $1.5 trillion House bill, the Bird-Safe Buildings Act of 2019 requires new and renovated public buildings to use materials and facade designs aimed at reducing bird collisions. This includes setting limits on how much glass a facade can have, and when glass is used, requirements that it be opaque, etched, stained, patterned, or coated with reflective material that is visible to birds. That bill is now awaiting attention in the Senate, where its prospects are unclear. Some cities, such as New York and Madison, Wisconsin, have passed ordinances requiring the use of bird-safe materials. “There’s progress, but there needs to be so much more,” Rowden says.

Architects are increasingly sensitive to the threats their buildings can pose, and many have begun to implement bird-safe features in their designs, including projects such as the Aqua Tower in Chicago, designed by Studio Gang, and the New York Times building, designed by Renzo Piano and FXFowle. But more work is needed to make buildings both old and new less deadly for birds. One challenge is the availability and cost of bird-friendly materials, Rowden says.

Though there may be no real way to fully understand why so many birds so suddenly collided with Philadelphia’s buildings, their deaths make an emphatic argument for these kinds of design and policy changes to be put in place as soon as possible.

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