Reference
Visser, M.E., Adriaensen, F., van Balen, J.H., Blondel, J., Dhondt, A.A., van Dongen, S., du Feu, C., Ivankina, E.V., Kerimov, A.B. de Laet, J., Matthysen, E., McCleery, R., Orell, M. and Thomson, D.L. 2003. Variable responses to large-scale climate change in European Parus populations. Proceedings of the Royal Society of London B 270: 367-372.
What was done
The authors examined laying dates of 24 populations of great and blue tits (Parus major and Parus caeruleus, respectively) in six European countries from 1979 to 1998, over which period several, but not all, of the locations studied exhibited increases in near-surface air temperature.
What was learned
The authors report that "the phenological response to large-scale changes in spring temperature varies across a species' range, even between populations situated close to each other." What is more, they find that "this variation cannot be fully explained by variation in the temperature change during the pre- and post-laying periods."
What it means
The authors say their results "show the value of replicating population studies across parts of a species' range, as the effects of climate change may differ, even within a single species, on a small geographical scale," thus suggesting to us that extremely great caution must be exercised so as not to conclude too much from studies of bird responses to global warming that are not massively replicated across large areas. Avoiding incorrect conclusions would appear to be a real challenge in this very complex field of study.
Reviewed 21 May 2003