The American robin increasingly spends winters in Colorado as temperatures rise. (Photo/USFWS, Lee Karney)

The American Robin increasingly spends winters in Colorado as temperatures rise. (Photo/USFWS, Lee Karney)

The first robin of spring usually warms the heart after a long winter in Colorado, but a study released last week by the National Audubon Society says the red-breasted harbingers have stopped leaving the state in the winter and herald warming of a different kind.

Over the past four decades, in late December American Robin counts in Colorado have increased more than 17-fold as migration patterns follow rising temperatures northward. It’s a trend found in a majority of species nationwide by the bird advocacy group, the Colorado Springs Gazette reports.

The Audubon Society rounded up data from Christmas bird counts conducted since 1966 to determine that 58 percent of the 305 bird species counted have shifted north — many by hundreds of miles — in the winter, according to an Audubon release. The winter range of American Robins (listen to one here) moved more than 200 miles north during the last 40 years, the Gazette’s Dave Phillips reports. Other species that had not wintered in Colorado — including magpies and wood ducks — have also moved north as average temperatures have risen, sometimes by as little as a single degree Fahrenheit.

“The birds are giving us yet another warning that it’s time for urgent action,” said Audubon President John Flicker in a release. “People hear about melting glaciers and changing weather, but now they can witness the impact global warming is having with the birds they see or don’t see right outside their doors.”

Even the data showing some species didn’t move north could be ominous, the Audubon Society notes: