New York City may be the very definition of a man-made environment, but the place is also teeming with nature. For example, Manhattan lies directly in the flight path of hundreds of thousands of birds as they migrate south in the autumn and north in the spring, and the uninhabited islands of New York are breeding grounds for scores of wild bird species.
However, the concrete and glass canyons of New York and other cities also pose a danger to birds, especially when cloudy nights force them to fly low.
Daniel Klem, a bird specialist at Muhlenburg College in Allentown Pennsylvania, says that, short of habitat destruction, the most serious human related threat for birds is sheet glass, simply because birds act as if they don't see it. "And they act as if they are attempting to reach habitat that is seen either on the other side of clear glass or mirrored or reflected in tinted panes. So they are deceived."
Birds are usually drawn to skyscrapers in the first place because of their exterior and office lighting, says Yigal Gelb of the New York City Audubon Society, an organization dedicated to protecting birds and other wildlife. "They are programmed over millions of years to pick up certain cues from the environment, like maybe stars or the moon or different luminous bodies." That probably has to do with their navigational system, says Mr. Gelb. "There have never been lights lighting up the skies like we do today. So in a very short time period relative to their evolution all these new sources of light came up, and their navigational system gets kind of confused."
That causes the birds to start circling the lights. "And when that happens," says Mr. Gelb, "they start losing precious energy which they need for migration, and they also run the risk of colliding either into the structures or into other birds."
Professor Daniel Klem says that even when they don't collide with buildings or each other, exhaustion from circling often compels birds to seek rest for the night. They flutter to the ground to sleep, only to wake in the daytime to new dangers. "They are now seeking out what cover they can find," he says. "Usually these are small little patches, little areas of vegetation." And it's at this time, says Mr. Klem, that they once again become vulnerable to the glass. "If there happens to be a tree or a shrub that is reflected in a pane, or if they happen to see habitat in the lobby of a large building where an atrium might exist and they attempt to reach it," he says, "they collide with the glass."
Efforts are being made to deal with the problem. One is the New York City's Audubon Society's "Lights Out New York" program in which owners and managers of buildings over 40 stories high are encouraged to help by dimming the decorative lights on the outside of their buildings, and to dim their office lights or use blinds, so that the buildings become darker. "They like to say that 'the city never sleeps,'" says Mr. Gelb, "but a lot of the city does sleep. Most of the people don't really sit and look at the skyline at 2:00 am."
Variants of this program have been in place in Chicago and Toronto, Canada, for some time, and research in both cities has shown the dimming strategy to be effective.
Scientists are also trying to invent new kinds of glass that will keep birds safe. Birds can see ultraviolet lights that humans cannot. One glass product currently in development will reflect patterns in the ultraviolet spectrum that will warn birds away, but retain the transparency that humans enjoy. Experts say that if all buildings in the United States used such glass, it could save many of the estimated one billion birds that are killed every year.