Study shows half of bird species in North America now winter farther north

Our feathery visitors are arriving in Michigan earlier and leaving later.

The National Audubon Society released a study Tuesday showing that more than half of 305 bird species in North America -- including robins, gulls, chickadees and owls -- are spending the winter about 35 miles farther north than 40 years ago.

Seventeen species -- including the Carolina wren, purple finch and tundra swan -- are spending more time in the Great Lakes Bay Region, said Caleb G. Putnam, Michigan important bird areas coordinator for the Audubon Society.

"The Carolina wren is one that may not have been here earlier but is now shifting north at a rapid pace," he said. "Forty years ago, you would have had a hard time seeing any in the Lower Peninsula."

The American robin, Michigan's state bird, is averaging 206 miles north of its winter range, Putnam said.

Joseph M. Soehnel, 55, of Essexville, who manages the Web site www.saginawbaybirding.org, said he's noticed that robins and Eastern bluebirds are coming earlier in the spring and staying later in the fall.

Soehnel's site documents record early dates and record late dates for birds in the region.

Overwintering "has a direct correlation" to global warming, he said.

"What forces migration is a lack of food source. You have a climate warming earlier in the spring, not appreciably, but enough for them to find food," he said.

During the 40 years the study covers, the nation's average January temperature climbed about 5 degrees Fahrenheit. The warming was most pronounced in northern states, with an influx of southern birds and possibly some northern species retreating to Canada.

Some doubt warming

Some regional naturalists believe the Audubon Society study neglects other factors.

Decreased pesticide levels, bird population growth and expanding forests are among possible reasons for the change in behavior, said Philip W. Stephens, senior naturalist at the Chippewa Nature Center near Midland.

"It's hard to say all this is happening because of climate change," he said.

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