"When it comes to global warming, the canary in the coal mine isn't a canary at all. It's a purple finch.
As the temperature across the U.S. has gotten warmer, the purple finch has been spending its winters more than 400 miles farther north than it used to.
And it's not alone.
An Audubon Society study to be released Tuesday found that more than half of 305 birds 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.
Over the 40 years covered by the study, the average January temperature in the United States climbed by about 5 degrees Fahrenheit. That warming was most pronounced in northern states, which have already recorded an influx of more southern species and could see some northern species retreat into Canada as ranges shift....
The sandhill crane, a large gray bird that migrates to the southern U.S. for the winter, has a range that expanded about 40 miles north in the last 40 years. This small movement has likely contributed to the bird's population explosion in Tennessee. The sandhill population has grown to a point that state wildlife officials are considering allowing the bird to be hunted."