When Birds Crash Into Buildings

ALTHOUGH it was daytime, the woodpecker flew straight into a skyscraper and plummeted to the ground. The bird did not see the glass. A kind pedestrian found the dazed bird and watched over it, hoping that it would revive. His hopes were soon realized when the bird chirped, stood up, ruffled its feathers, and flew away. *

Sadly, not all birds survive such collisions unharmed. In fact, of those that fly into houses, about half die. Studies indicate that in the United States alone, more than 100 million birds die annually after crashing into buildings of various kinds, says the Audubon Society. And some researchers believe that the figure may be closer to a billion! Why, though, do birds fly into buildings? And can anything be done to make their life on the wing safer?

The Killers​—Glass and Light

Glass spells danger for birds. When windows are clean and clear, birds often see only what is on the other side, which may include greenery and sky. As a result, unsuspecting birds sometimes fly straight into the glass at full speed. Also, they may see decorative plants inside glass lobbies or homes and try to land on them.

Coated reflective glass can also be a problem. Under certain conditions, birds may see, not the glass, but a reflection of the surrounding area or sky and, here again, come  to grief. Birds have even been killed by glass at visitors’ centers and on observation towers at bird sanctuaries and wildlife refuges! Ornithologist and biology professor Dr. Daniel Klem, Jr., believes that more birds are killed by flying into windows than by any other cause related to human activity, except perhaps habitat destruction.

Some birds are especially vulnerable to crashes. Most migratory songbirds, for example, fly toward their destination at night and navigate, at least in part, by the stars. As a result, they may become confused by bright lights on tall buildings. Indeed, some birds have become so disoriented that they have flown around aimlessly until they dropped from exhaustion. Another danger occurs during nights of rain or high cloud cover. On such occasions, birds tend to fly at lower altitudes, which increases their risk of crashing into tall buildings.

The Impact on Bird Populations

Just one tall building in Chicago, Illinois, U.S.A., caused an average of about 1,480 known deaths during migration season, according to one report. Thus, over a period of 14 consecutive years, that one building caused the death of some 20,700 birds. Of course, the total number of bird strikes was no doubt much higher. Moreover, these birds “are not the pigeons, gulls, or geese,” says Michael Mesure, director of the Fatal Light Awareness Program of Toronto, Canada, but “birds with endangered populations.”

For example, in Australia in one recent year, glass killed about 30 swift parrots, of which only 2,000 remain. In the United States, many museum specimens of Bachman’s warbler, now possibly extinct, were gathered from collisions with one particular lighthouse in Florida.

Of the birds that survive building strikes, many are injured or weakened. This can be especially hazardous for migratory birds. If they are hurt and come down within a concentration of buildings, they may die of hunger or predation by other animals, some of which have learned to exploit this occasional food source.

Can Buildings Be Made Bird Friendly?

For birds to avoid flying into glass, they need to see it and recognize it as a solid object. To that end, some homeowners have sacrificed their view somewhat by attaching decals, stickers, or other readily visible matter to the outside of windows subject to bird strikes. According to Klem, the important thing is, not the drawings or the stickers themselves, but the spacing. His research suggests that visual cues should be no more than two inches [5 cm] apart horizontally and four inches [10 cm] vertically.

What can be done to help night-flying migratory birds? “Nocturnal collision with buildings . . . is largely preventable with the flick of a switch,” says ecological research consultant Lesley J. Evans Ogden. In some cities, decorative lights on skyscrapers are now being dimmed or turned off at a set hour of the night, especially during bird-migration season. In other instances, netting has been placed on windows of tall buildings so that birds do not mistake reflections for sky.

Such measures may reduce the death toll by as much as 80 percent, saving millions of birds annually. But the basic problem likely will not go away, for people love lights and glass. Hence, organizations devoted to the welfare of birds, such as the Audubon Society, are attempting to persuade architects and developers to be more sensitive to the needs of the natural world.

[Footnote]

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WHERE HAVE ALL THE BIRDS GONE?

Estimates of annual human-associated bird deaths in the United States

▪ Communication towers​—40 million

▪ Pesticides​—74 million

▪ House cats and feral cats​—365 million

▪ Glass windows​—100 million to 1 billion

▪ Loss of habitat​—unknown, but possibly the most harmful factor

[Picture on page 10]

Each year in the United States, at least 100 million birds die after crashing into windows

[Credit Line]

© Reimar Gaertner/​age fotostock