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North American Birds in a Warming World
Reference
Hitch, A.T. and Leberg, P.L. 2007. Breeding distributions of North American bird species moving north as a result of climate change. Conservation Biology 21: 534-539.

What was done
For the portion of the United States located east of the Rocky Mountains, the authors used data from the North American Breeding Bird Survey to evaluate shifts in the northern range boundaries of 26 species of birds with southern distributions and the southern range boundaries of 29 species of birds with northern distributions between the periods 1967-1971 and 1998-2002, when climate alarmists claim the earth warmed at a rate and to a level that was unprecedented over the past one to two millennia.

What was learned
Hitch and Leberg report that the northern margins of the southern group of birds showed significant northward shifts that averaged 2.35 km/year for all species studied, which finding they describe as being "consistent with the results of Thomas and Lennon (1999) from Great Britain." Also in agreement with the behavior of British birds, they report that "the levels of warming do not appear to be so great they are forcing birds to abandon the southernmost portions of their distributions."

What it means
As is the case in many parts of the planet (see Birds in our Subject Index), the world's birds appear to be enlarging their ranges in response to global warming. Consequently, whereas climate alarmists claim that rising temperatures will tend to drive plants and animals of all kinds to extinction due to warming-induced range contractions, just the opposite would appear to be the case with the planet's birds, as it is with most of the world's other plants and animals (see our major report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?). And we note that these range expansions are occurring in spite of the supposedly unprecedented global warming of the past few decades.

Reference
Thomas, C.D. and Lennon, J.J. 1999. Birds extend their ranges northwards. Nature 399: 213.

Reviewed 15 October 2008