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Climate Change Affects Migration

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The Associated Press

Published: February 11, 2009

WASHINGTON - When it comes to global warming, the canary in the coal mine isn't a canary. It's a purple finch.

As the temperature across the United States has risen, the purple finch has been spending its winters more than 400 miles farther north than it used to.

It's not alone.

An Audubon Society study released Tuesday found that more than half of 305 bird species in North America, a hodgepodge that includes robins, gulls, chickadees and owls, are spending the winter about 35 miles farther north than they did 40 years ago.

The purple finch was the biggest northward mover. Its wintering grounds now are more along the latitude of Milwaukee, Wis., instead of Springfield, Mo.
Bird ranges can expand and shift for many reasons, among them urban sprawl, deforestation and the supplemental diet provided by backyard feeders. Researchers say the only explanation for why so many birds over such a broad area are wintering in more northern locales is global warming.

In the 40 years covered by the study, the average January temperature in the United States climbed by about 5 degrees. That warming was most pronounced in northern states, which already have recorded an influx of more southern species and could see some northern species retreat into Canada as ranges shift.

"This is as close as science at this scale gets to proof," said Greg Butcher, the lead scientist on the study and the director of bird conservation at the Audubon Society. "It is not what each of these individual birds did. It is the wide diversity of birds that suggests it has something to do with temperature rather than ecology."

Previous studies of breeding birds in Great Britain and the eastern United States have detected similar trends, but the Audubon study covered a broader area and included many more species. The study of migration habits from 1966 through 2005 found about one-fourth of the species have moved farther south. The number moving north, 177 species, is twice that.

The research is based on data collected during the Audubon Society's Christmas Bird Count in early winter.

To survive the cold, birds need to eat enough during the day to have the energy to shiver throughout the night.

Research can't explain why particular species are moving. That's because changes in temperature affect different birds in different ways.

IN FLORIDA

Birds and the estimated miles they have moved north in the past 40 years:

•Rusty blackbird, 100.9

•Northern bobwhite, 85.7

•Brewer's blackbird, 13.6

•Northern pintail, 91.0

•White-throated sparrow, 109.1

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