Common bird species in dramatic decline

A new Audubon study is one of the most comprehensive looks at bird-population trends in North America.

from the June 15, 2007 edition

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Crows, bluebirds, mourning doves, and robins are wintering farther north and their populations are still robust, Dr. Butcher says. But other species that rely on cold climates, like the snow bunting and greater scaup, which breed in Alaskan and Canadian tundra, are showing signs of trouble. As the tundra warms, it cedes to shrubs unsuitable for the birds to breed, Butcher says. Scaup numbers are down 75 percent and bunting 64 percent, in part because these species can't go farther north to breed.

Although populations in some cases dip as low as 500,000 globally, none of the "common" bird species cited is in danger of extinction, Butcher notes. But their struggle mirrors a larger global trend among endangered migratory songbirds and tropical species.

At the current rate, global warming and destroyed bird habitat could lead to the significant decline or extinction of at least 400 of the world's 8,750 bird species, reported another new study, this one focused on climate-change impact. Under certain scenarios, 750 to 1,800 bird species could be imperiled by the year 2100, the study released earlier this month reported.

Most of the threatened populations are in the tropics and are in danger due to slashing of their rain-forest habitat – but global warming is a clearly a looming threat, says Walter Jetz, an assistant professor of biological sciences at the University of California at San Diego and lead author of the study.

"It's true some birds are responding already to climate change by moving farther north and leaving later in fall and coming back earlier," he says. "But there's a limit to that. At some point, there's going to be real trouble because of the impact and distortions on migration routes that have evolved over millions of years."

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