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Birds of the Italian Alps: Their Response to Recent Warming
Popy, S., Bordignon, L. and Prodon, R. 2010. A weak upward elevational shift in the distributions of breeding birds in the Italian Alps. Journal of Biogeography 37: 57-67.

The validity of the climate envelope approach for predicting shifts in species' ranges in response to global warming has come under fire for a number of inherent weaknesses, as discussed by Nogues-Bravo (2009) for all species in general, and by Beale et al. (2008), who demonstrated that "species-climate associations found by climate envelope methods are no better than chance for 68 of 100 European bird species."

What was done
In a further study of the utility of the climate envelope concept that was conducted in an alpine valley in the Italian Piedmont, Popy et al. employed data from two bird atlas surveys performed on a 1-km by 1-km grid (the first in 1992-94 and the second in 2003-05) in an attempt to see if there was any evidence for an expected upward shift in the ranges of 75 bird species (68 of which were detected in both surveys) over this period, during which time mean air temperature rose by a full 1.0C.

What was learned
The three researchers report that "the number of species whose mean elevation increased (n = 42) was higher than the number whose mean elevation decreased (n = 19), but the overall upward shift [29 m] was not significantly different from zero." In addition, they state that even the 29-m increase was "smaller than would be expected from 'climatic envelope' models," as the "1.0C increase in temperature would be equivalent to c. 200 m in elevation, based on an average gradient of -0.5C per 100 m." In addition, they indicate that "at the European scale, no overall expansion or contraction of the distributions of the studied species was detected."

What it means
In light of their findings, as well as those of others they cite, Popy et al. conclude that "until a better understanding of the underlying mechanisms is achieved, predictions based only on 'climate envelope' models should be either validated or considered cautiously," which in our view is a pretty generous conclusion. We would suggest that such poorly-performing models not be used at all.

Beale, C.M., Lennon, J.J. and Gimona, A. 2008. Opening the climate envelope reveals no macroscale associations with climate in European birds. Proceedings of the National Academy of Sciences USA 105: 14,908-14,912.

Nogues-Bravo, D. 2009. Predicting the past distribution of species climatic niches. Global Ecology and Biogeography 18: 521-531.

Reviewed 7 April 2010