North American Bird Breeding Ranges Moving Quickly Northward - Conservation Biology Article

Breeding ranges of North American birds have shifted northward coinciding with a period of increasing global temperatures, report researchers writing in the April issue of Conservation Biology.

Studying the breeding ranges of 56 species of arboreal and semiarboreal birds using data collected by the North American Breeding Bird Survey, Auburn University researchers Alan Hitch and Paul Leberg sought to determine whether factors — including population expansions and land-use changes — other than climate that might explain the observed range shift. "To demonstrate a causal link between climate change and shifting ranges is difficult," said Hitch, a doctoral student with Auburn University’s School of Forestry and Wildlife Sciences. "If breeding ranges were moving because of climate change, then the effect should be seen among multiple species over large scales."

Were bird ranges expanding both northward and southward, Hitch says then the data would suggest that the birds were simply expanding their ranges. However, Hitch and Leberg "found that the birds' ranges were only expanding northward leading to the conclusion that climate change might be responsible for the shift in range," according to a statement from Auburn University.

"It was important to determine whether climate change was the likely cause of the range shift," he said. "The fact that the northward shift in North America was similar to that seen in an earlier study conducted in Great Britain, gives us some support for that conclusion."

EDIT

http://news.mongabay.com/2008/0116-birds.html