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(AP) - 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.


      An Audubon Society study 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.


      The purple finch was the biggest northward mover. Its wintering
grounds are now 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. 


But researchers say the only explanation for why
so many birds over such a broad area are wintering in more northern
locales is global warming.


      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.


      "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."


      The study provides compelling evidence for what many birders
across the country have long recognized - that many birds are
responding to climate change by shifting farther north.


      Previous studies of breeding birds in Great Britain and the
eastern U.S. have detected similar trends. But the Audubon study
covers a broader area and includes many more species.


      The study of migration habits from 1966 through 2005 found about
one-fourth of the species have moved farther south. But the number
moving northward - 177 species - is twice that.


      The study "shows a very, very large fraction of the wintering
birds are shifting" northward, said Terry Root, a biologist at
Stanford University. "We don't know for a fact that it is warming.
But when one keeps finding the same thing over and over ... we know
it is not just a figment of our imagination."


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


At that time of
year, temperature is the primary driver for where birds go and
whether they live or die. To survive the cold, birds need to eat
enough during the day to have the energy needed to shiver
throughout the night.


      Milder winters mean the birds don't need to expend as much
energy shivering, and can get by eating less food in the day.


      General biology aside, the research can't explain why particular
species are moving. That's because changes in temperature affect
different birds in different ways.


      Some birds will expand their range farther north. For example,
the Carolina wren - the state bird of South Carolina - has turned
into a Yankee, based on Audubon's calculations. It is now commonly
seen in the winter well into New England, as well as its namesake
state of South Carolina.


      "Twenty years ago, I remember people driving hours to see the
one Carolina wren in the state," said Jeff Wells, an ornithologist
based in southern Maine. "Now, every year I get two or three just
in my area," he said. "Obviously, things have changed."


      Other species, such as the purple finch and boreal chickadee,
spend their summers in the forests of Canada and fly south into the
U.S. for the winter. 


Climate change could be playing a role in why
they are not flying as far south as they used to, and are no longer
as common as they were in states like Maine, Vermont and Wisconsin.


      For other species, global warming may not be a major factor in
the movements measured by Audubon at all. The wild turkey was
second only to the purple finch in miles moved north - about 400.
But it's likely due to efforts by hunters and state wildlife
managers to boost its population.


      In other cases, the range shifts are prompting calls to cull
some bird populations.


      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.


      "You are seeing it all across the state," said Richard
Connors, president of the Tennessee Ornithological Society. "As it
increases, there is going to be pressure to hunt it. The bird
watchers of Tennessee don't want that."
      

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Environmental News

As the temperature across the U.S. has gotten warmer, more than 300 species of birds have been spending their winters farther north than they  used to.

Study: Birds shifting north due to global warming

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