Nov. 13, 2006 — -- Bird-watching is a classic American pastime; over $30 billion a year is spent on the hobby. We love to watch birds when they are in our backyards -- their native habitats -- but few of us realize the dangers the birds face during their seasonal migrations.
Between 100 million and one billion birds are killed every year in the United States when they crash into glass windows. And even one billion deaths might be a conservative estimate, says ornithologist Daniel Klem Jr. of Muhlenberg College in Allentown, Pa.
At that upper estimate, it would take approximately 3,000 Exxon Valdez oil spills to match one year's death toll due to glass collisions, says Klem, who has studied the causes of bird fatalities for more than 30 years.
And until recently, he says, the conservation community has not paid attention to the problem "because there's no easy solution."
"There are billions of dollars spent on bird watching," Klem told ABC News. "Acquaintances that I know that are so avid and so knowledgeable about birding -- they're totally clueless about this. It's like our populations are bleeding away, and they're not able to be replenished."
Most of the fatalities come during the spring and fall migrations, when billions of birds cross the country as they travel great distances -- sometimes as far as from Central America to Canada.
The problem is that the glass in buildings is as invisible to birds as it is to people. "By day, birds see sky, clouds and trees reflected in glass facades and they 'think' that they can fly into it," explains industrial ornithologist Richard Podolsky.
"And by night, especially foggy nights when the top of the Empire State Building is draped in fog, birds fixate on lights and fly towards them or around them and crash into buildings."
"We now are building these all-glass buildings everywhere," said New York architect Bruce Fowle. By adding more trees to our cities, says Fowle, "We're enhancing the bird habitat ... At the same time we're creating these killers."
Dr. Podolsky has been advising the developers of New York's 1,776-foot Freedom Tower, which will be built on the site of the World Trade Center and will incorporate innovative designs to reduce bird deaths.
His recommendations: use as little reflective glass as possible at lower levels; position trees and vegetation to minimize their reflections in the glass; and avoid planting trees in atriums with a clear facade.
Podolsky has also proposed a "collision mitigation system" to deter birds from striking the tower at night.
"We hope to have a system in place that will use radar to detect birds approaching the upper floors of the Freedom Tower, and indeed other tall buildings in Lower Manhattan, and dim down the lights that will be used to illuminate the antenna and sculpture at the top of the building," Podolsky told ABC News.
"In this way, birds migrating down the Hudson or East Rivers or along the Atlantic Flyway will not be attracted to the lights of the Freedom Tower … This is especially important during the fall and spring migrations when many birds are flying north or south over Manhattan."
The Tower's developers have already integrated Podolsky's advice into its plans. The first 186 feet will have wavy textured window glass that will use prisms to "look as solid as stone to a bird," says Jeffrey Holmes of the architecture firm Skidmore, Owings, and Merrill.
It's fitting that the Freedom Tower is taking these steps, because the twin towers of the World Trade Center caused so many bird collisions that in 1997 the New York City Audubon Society created Project Safe Flight to monitor bird collisions at the site.
ABC News recently joined Nicole Delacretaz, manager of Project Safe Flight, as she looked for downed birds at the U.S. Postal Service's Morgan Mail Processing building on Manhattan's West Side, considered by NYCAS to be the deadliest site for birds in the city. NYCAS has documented more than 300 bird fatalities outside the building during this fall's migration season.
The building attracts so many birds because of the trees on the sidewalk around the building and in a park across the street. The building is only six stories high, but its windows are opaque and highly reflective of the vegetation and sky.
The U.S. Postal Service is eager to resolve the problem, according to Yigal Gelb, Project Director of NYCAS. The USPS plans to hire a contractor to etch or sandblast the windows to make them less reflective.
ABC News got an advance look at a study prepared by NYCAS that examines the role of windows and vegetation in bird collisions. The study found that the further the vegetation is from the window, the more lethal the site becomes because the increased distance allows the bird to gain momentum and hit the window with greater force.
While many people think that most bird collisions occur at night, "It's exactly the reverse," said Gelb. "Light might be playing a role in attracting the birds to the city but the collisions really happen the day after, when they wake up and start feeding and collide into these death traps."
Interestingly, home grown "urban birds" like pigeons, sparrows and starlings seem to have figured out how to safely navigate the glass canyons of New York; the top 20 bird species involved in collisions were all migrants. The top five species involved in collisions are White-throated Sparrow, Common Yellowthroat, Ovenbird, Dark-eyed Junco, and Ruby-crowned Kinglet.
Although the city birds were abundant in the areas surveyed, Audubon found only eight pigeons and 17 sparrows were involved in collisions.
While it's possible that natural bird behavior may keep these "urban birds" out of trouble, some ornithologists believe that these street-savvy birds may have developed a way to avoid colliding with windows. But no one knows for sure.
Audubon International lists additional ways to make buildings and homes more bird-friendly:
To find out how to help a bird that has flown into a building, click here