Birds' movements reveal global warming threat.

• Position: Avian Migration

Analyses of citizen-gathered data from the past 40 years of Audubon's Christmas Bird Count reveal that 58% of the 305 widespread species that winter on the continent have shifted significantly north since 1968, some by hundreds of miles. Movement was detected among species of every type, including more than 70% of highly adaptable forest and feeder birds. Only 38% of grassland species mirrored the trend, reflecting the constraints of their severely-depleted habitat and suggesting that they now face a double threat from the combined stresses of habitat loss and climate adaptation.

Population shifts among individual species are common, fluctuate, and can have many causes. However, Audubon scientists say the ongoing trend of movement by some 177 species--closely correlated to long-term winter temperature increases--reveals an undeniable link to the changing climate.

"Birds are showing us how the heavy hand of humanity is tipping the balance of nature and causing ecological disruption in ways we are just beginning to predict and comprehend," maintains Greg Butcher, director of Bird Conservation. "Common sense dictates that we act now to curb the causes and impacts of global warming to the extent we can, and shape our policies to better cope with the disruptions we cannot avoid."

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Movement across all species--including those not reflecting...