By Leslie Kaufman, The New York Times, January 18, 2011
|A red winged blackbird|
At the beginning of this month when about 5,000 red-winged blackbirds fell from the sky in one night in Arkansas, biologists were called on to put a damper on public speculation about pesticides and secret military tests by reminding everyone how many birds there are and how many die. They often do so as a result of human activity, but in far more mundane and dispiriting ways than conspiracy buffs might imagine.
“Five billion birds die in the U.S. every year,” said Melanie Driscoll, a biologist and director of bird conservation for the Gulf of Mexico and Mississippi Flyway for the National Audubon Society.
That means that on average, 13.7 million birds die in this country every day. This number, while large, needs to be put into context. The federal Fish and Wildlife Service estimates that a minimum of 10 billion birds breed in the United States every year and that as many as 20 billion may be in the country during the fall migratory season.
Even without humans, tens of millions of birds would be lost each year to natural predators and natural accidents — millions of fledglings die during their first attempts at flight. But according to the Fish and Wildlife Service, people have severely complicated the task of survival. Although mortality rates are difficult to calculate for certain, using modeling and other methods like extrapolation from local research findings, the government has come up with estimates of how many birds die from various causes in the United States.
Some of the biggest death traps are surprising. Almost everyone has an experience with a pet proudly bringing home a songbird in its jaws. Nationally, domestic and feral cats kill hundreds of millions of birds each year, according to the government. One study done in Wisconsin found that domestic rural cats alone (thus excluding a large number of suburban and urban cats) killed roughly 39 million birds a year.
Pesticides kill 72 million birds directly, but an unknown and probably larger number ingest the poisons and die later unseen. Orphaned chicks also go uncounted.
And then there is flying into objects, which is most likely what killed the birds in Arkansas. The government estimates that strikes against building windows alone account for anywhere from 97 million to nearly 976 million bird deaths a year. Cars kill another 60 million or so. High-tension transmission and power distribution lines are also deadly obstacles. Extrapolating from European studies, the Fish and Wildlife Service estimates 174 million birds die each year by flying into these wires. None of these numbers take into account the largest killer of birds in America: loss of habitat to development.
All of this explains why about a quarter of the 836 species of birds protected under the Migratory Bird Treaty Act are in serious decline. For a third of the other birds there is not enough information to be sure about the health of their populations.
Of course, poisons and electric wires are not as exciting to think about as secret government plots, but Ms. Driscoll says it is time we pay attention to them anyway.
“It is the story that the press and the public have largely missed, and it is important, and timely, given the current concern,” she said. “And it is what gets those of us who work in bird conservation motivated every day to try to deal with human-induced changes to our habitats, our landscape and our very climate.”