Philadelphia’s glass skyline is killing birds. A new Fairmount Park building has a solution.

Philadelphia's glittery, and ever-expanding skyline, is a thing of beauty — at least to the human eye. If you're a bird, though, it's a death trap.

In late August, I went for a stroll along the Schuylkill waterfront, which has filled in over the last decade with an impressive lineup of sleek glass towers. The river is a major flyway for birds migrating between Canada and South America, and as I looped around the Roberts Center for Pediatric Research, next to the South Street Bridge, I spotted a clear casualty of all that development: a dead, female American redstart warbler. It had slammed into the glass facade and died instantly.

A few weeks later, I took the same walk. Another dead warbler lay in the same spot.

No one knows precisely how many birds are killing themselves in Center City, but ornithologists believe that between 350 million and a billion birds in the United States die every year from flying into buildings. They mistake the reflections in the windows for real trees and shrubs, and then dart into the glass at top speed. Yet, despite the disturbing avian death toll, the same kind of shimmery skyline that has emerged along the Schuylkill is rising in cities all over America. Some species of songbirds, already vulnerable to disease and habitat loss, may not survive the current building boom.

Somehow, builders and architects remain largely in denial about their contribution to the crisis. Both know that people love being inside glass towers because they offer astounding views. From a distance, their reflective skins seem to melt into the sky. But it's developers who are the ones really committed to building with glass. Cheaper and easier to install than many of the alternatives, glass cladding is unlikely to go away anytime soon.

The thing is, it wouldn't take much to significantly reduce the carnage. Just a short distance upstream from Center City's soaring glass towers is a modest new structure that bills itself as Philadelphia's first totally bird-safe building. Called the Discovery Center, it demonstrates that we can enjoy both birds and buildings.

The little pavilion is the new home of Audubon Pennsylvania and Outward Bound, two nonprofits that joined forces to rescue a forgotten reservoir deep inside Fairmount Park. Once the city's main source of drinking water, the reservoir was shut down in the 1970s and barricaded behind a high fence. Over time, the 37-acre basin evolved into Philadelphia's largest bird sanctuary, a way station for 170 species. The man-made lake was the perfect base for the two groups, so they made a deal with the city to manage the property and reopen it to the public.

Since the work of Audubon and Outward Bound revolves around nature, they wanted their new headquarters to have expansive views of the birds and the water. But because they also see themselves as environmental champions, they knew it wouldn't do to have birds crashing into the picture windows.

Birds generally migrate at night, when the winds are lighter. Every few days, they stop to rest and feed. Because of the way their vision works, they are drawn to points of light in the midst of darkness, says Christine Sheppard, a bird collisions expert at the American Bird Conservancy.

Nearly half the crashes actually occur in the suburbs, where large picture windows reflect nearby trees. But urban buildings account for the other half. Things are so bad at the Minnesota Vikings' new glass-enclosed U.S. Bank Arena that crews must come out every morning to sweep up the dead birds. Ironically, recent improvements in glassmaking technology that make such buildings possible, also have made it more difficult for birds to recognize the hard surface. Unlike the wavy glass of the 19th century, today's panels are flawless.

Enter Digsau, the Philadelphia architects who gave us the jaunty pavilion at Logan Square's Sister Cities Park and are known for creating buildings out of recycled materials. While they had never designed a bird-safe building before, others had.

Many of the techniques they used at the Discovery Center were developed by Daniel Klem, a professor of ornithology at Muhlenberg College in Allentown. He found that glass etched with translucent lines or dots could help birds recognize the presence of a solid wall. In 2014, his ideas were put to the test when the Javits Convention Center — once known as New York's deadliest bird-killer — was reclad with dotted glass by FXCollaborative. Now it's the most bird-friendly building in town.

That kind of glass is expensive, so Digsau's Jules Dingle limited its use to the Discovery's Center's signature feature, a 30-foot, rock-climbing tower, which looks out over the reservoir. The rest of the building, which includes offices and conference rooms, hugs the ground along the park's Reservoir Drive, in the Strawberry Mansion neighborhood across the road from Smith Playground.

Like many Digsau buildings, the design is deeply textured and hinges in interesting ways. You enter the site through an angled portal that has been shaped to reveal the lush expanse of the old reservoir in one powerful frame.

Although the building is clad in cedar wood, it boasts a wall of windows overlooking the water. Dingle screened some with wood slats. For the rest, he came up with an ingenious solution that cost all of $275: He strung a curtain of plastic cord over the windows. In another location, he pasted plastic decals on the glass.

By using a variety of strategies, Dingle believes the Discovery Center can serve as a showroom of bird-friendly hacks. The building is considered so safe that Dingle even embedded nesting boxes into the cedar facade, which was given a charred black, waterproof coating using the Japanese shou sugi ban method.

Obviously, not all these tricks will work on a glass skyscraper. But etched and dotted glass are frequently employed by architects to reduce sun glare and heat. You can see the material on the Erdy McHenry's Evo, which may be the most bird-friendly tower on the Schuylkill.

The reason the etched, or fritted, glass isn't used more often is that it interferes with the fantasy that there is nothing between the viewer and the great outdoors. But once the eye adapts, the views are still magnificent. The momentary adjustment is a small price to pay for saving millions of birds.

Several states, including California and Minnesota, have adopted laws requiring bird-friendly designs. Why not Philadelphia? It's a lot better option than sweeping up the dead birds in the morning.