Fatal reflections

As 'green' architecture advances, glass buildings pose hazard to birds

By Bina Venkataraman
Globe Correspondent / December 15, 2008
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Boston is striving to become a leader in green building. But glass siding and atriums, common features of green architecture, carry an unintended side-effect: a mortal danger to birds.

An estimated 5 percent of the country's bird population - or about a billion birds - die each year by crashing into buildings they cannot see, according to Daniel Klem, an ornithologist at Muhlenberg College in Pennsylvania who has studied bird collisions for more than 30 years. Migratory birds, including songbirds whose populations are already on the decline, crash into glass in especially large numbers.

While environmentalists often express concern about the effects of wind turbines and oil spills on birds, few realize that building collision is the second biggest cause of death to birds after habitat destruction, said Karen Imparato Cotton of the American Bird Conservancy.

And that danger is increasing as cities, Boston among them, erect buildings that emphasize natural light, and as improvements in the energy efficiency of glass increase its use.

Two properties of glass that make it so appealing - the way it reflects light and allows us to see through it - are the very reason that birds crash into it. In the windows and glass facades of buildings, birds see mirror-images of trees, sky, and shrubs they want to fly toward, or they may see food, water, or habitat inside or beyond atriums.

The effect of such architecture "flies in the face of conscientious green design," said Hillary Brown, principal for New Civic Works in New York.

Unlike Chicago and New York, Boston does not have a cadre of volunteers that count bird collisions into buildings. In those cities, dozens, sometimes hundreds, of birders go out in the early hours during bird migration in the spring and fall to collect and identify species of birds that crash into buildings.

They use the information to persuade building owners to put up bird-friendly safeguards, such as nets to create a buffer for flying birds, decals, or thin vinyl films that dull the mirror effect of glass facades. Last year, the US Postal Service spent more than $200,000 on such a film to reduce bird kills on a Manhattan building after a local Audubon volunteer corps counted more than 330 dead birds near it during a 2 1/2-month period.

"It is an issue that we have to address if we are going to have healthy bird populations," said Klem.

A few months ago, Boston did start a campaign to dim or turn out lights seasonally to deal with another cause of bird collisions - skyscraper lights that disorient migrating birds that navigate by stars. The owners of high-profile properties such as the John Hancock Tower turned down their lights after midnight for several weeks this fall, during migration season.

There is no recent bird death data for specific Boston buildings, although a 1970s study documented large kills from birds striking the glass of the Prudential Center in Back Bay. Reports from other urban areas paint a grim picture. A count at an office building on Long Island found that over eight days, 72 birds died after flying into the glass sides of the structure, according to New York City Audubon.

"Hundreds of thousands of birds move through the Northeast and the Boston area," said Jack Clarke, public policy director for Mass Audubon. Any tall buildings, Clarke said, are likely to have birds crashing into them.

Roof gardens, aimed at decreasing runoff and improving energy efficiency in buildings, also contribute to bird kills by attracting birds too close to plated glass, said Kate Orff, a landscape architect and professor at Columbia University's Graduate School of Architecture. "Green roofs are all the rage now," said Orff, speaking at the recent GreenBuild International Conference in Boston. "This has become a crucial problem in contemporary architecture," she said.

Several architects and ornithologists are working to combat the problem. But "it's very difficult to convince a developer these days that they shouldn't have floor-to-ceiling glass," said Bruce Fowle, senior partner at FxFowle Architects, the firm that designed the prism-like Conde Nast building in Times Square.

Toronto and Chicago have adopted bird-safe design recommendations, penned by avianophile architects, that encourage features such as "fritted" or patterned glass and "visual noise" - such as ceramic rods placed over the glass - to separate windows from bird life.

Other examples include the Minneapolis Central Library, where rows of birch trees were planted within 3 feet of glass facades to keep birds from crashing into them. The Illinois Institute of Technology's student center in Chicago has a "dot matrix" pattern in its glass that makes it less transparent and reflective to birds, according to design guides.

But even for many ecoconscious building owners and developers, the price of preventing bird kills is too high. "There's no easy answer to this," said Brown, of New Civic Works in New York, who wrote the city's bird-safe design guidelines. "But we can at least get people to think about compromises."

Fowle, the architect, is campaigning to have bird-friendly design incorporated into the US Green Building Council's certification system. Known as LEED, this is the seal of approval that Mayor Thomas M. Menino pledged to seek for all city buildings of a certain size.

The best fix, said Fowle, would be to make glass differently. A German company makes a UV-striped glass that is translucent to humans but detectable by birds. But the problem, Fowle said, is that it costs about 30 percent more than other high-performing glass.

Fowle's wife, Marcia, a board member of New York City Audubon, said that years ago, she told her husband that a building that uses recycled material and runs on solar power is not green enough.

"You can't be green and kill something," she said. "It's a contradiction."

Bina Venkataraman can be reached at

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