Energy Management

More birds stay north during winter months Audubon Society sees it as evidence of climate change
Feb 11, 2009
Chicago Tribune
Michael Hawthorne
Feb. 11, 2009 (McClatchy-Tribune Regional News delivered by Newstex) -- Once a harbinger of spring in the Chicago area, the American robin increasingly is hanging around for the winter too.
Their familiar dawn-to-dusk caroling might not be as prevalent when snow is on the ground. But robins are among scores of bird species that are steadily moving northward as average temperatures across the United States get higher, according to an Audubon Society study released Tuesday.
More than half of the 305 species in North America are spending winters at least 35 miles farther north than they did 40 years ago, the study found. During the same period, the nation's average January temperature rose about 5 degrees Fahrenheit.
While the changes appear to be less significant in Illinois than in other parts of the nation, nearly 20 bird species in the state have shifted their ranges farther north, the study found. Robins moved the farthest among species seen locally, and now are wintering about 200 miles north of where they did four decades ago.
Other transients include the turkey vulture, Eastern bluebird and hermit thrush, all of which now are seen more frequently in the Chicago area during the winter. Meanwhile, some species rarely seen in Illinois, such as the rough-legged hawk and pine siskin, have become virtual no-shows because they hang out even farther north nowadays.
Researchers say the findings are another sign that climate change is having direct effects far beyond the Arctic and Antarctic. It also backs up anecdotal evidence collected by birders, who have speculated for years that rising global temperatures are leading many species north.
"Some of these birds have almost vanished from the state during the winter," said Judy Pollock, director of bird conservation for the Audubon Chicago Region. "Others are being seen in far greater numbers, drawn perhaps by warmer temperatures and more abundant food supplies."
Indeed, bird ranges can change for various reasons, including habitat loss from urban sprawl and deforestation. Even backyard feeders can have an impact. But authors of the Audubon study said climate change is the only plausible reason so many different birds across the U.S. have shifted north during the past four decades.
Doug Stotz, a conservation ornithologist at the Field Museum, said researchers are just beginning to understand how changes in temperature, vegetation and food supplies are affecting different species. Local biologists have focused more intently on other threats, including loss of habitats and bird crashes into skyscrapers.
The Audubon study is limited to data from the society's Christmas Bird Count, and more research is needed to discover how species are affected during the spring breeding season, Stotz said.
For example, earlier springs might spawn bursts of insects before migratory birds arrive from wintering grounds farther south, meaning the birds would have less to eat when they get here. Changes in vegetation also could play a role if trees and shrubs bud before or after birds fly through the area.
Nationwide, the Audubon study found that one-fourth of the species tracked wintered farther south between 1966 and 2005. The number moving farther north, though, is twice that.
Audubon officials said the study should help support legislation pending before Congress that would cap heat-trapping carbon dioxide emissions for the first time. President Barack Obama has set a target of reducing carbon dioxide and other greenhouse gases by 80 percent by 2050.
"These birds are like canaries in the coal mine," said John Flicker, Audubon's president. "We are witnessing an uncontrolled experiment on the birds and the world we share with them."
Climate change affects each species differently. But the Audubon study suggests that birds in some cases adapt better than other species.
"Some of these birds have moved hundreds of miles," Stotz said. "It takes centuries for a snake to pull that off."