December 12, 2006

Global Warming Good for Mediterranean Tits?

Filed under: Adaptation, Animals

When some people think of a trip to the Mediterranean, they think there is a good chance to see a wide variety of tits, and for those of you interested in global warming, you might fairly wonder how climate change in the Mediterranean might change this situation. Well, you are in luck given an article in the most recent issue of Global Change Biology that specifically addresses potential climate impacts on Mediterranean tits. There are certainly many tits to study in that region, and there is no doubt that any change in climate could have an impact on their characteristics. To us at World Climate Report, this sounds like an important issue and we applaud any effort to explore climate change and tits throughout the planet.

An international team of tit experts from France, Belgium, and Canada note that “Climate change over the past century has had important ecological consequences, but predictions concerning the impact of future climate change on biodiversity remain subject to large uncertainties.” As tits are hardly confined to the Mediterranean, this work could provide insights into tit response in many other regions. World Climate Report has focused on tits in the past (see our story “Great tit watching in the British Isles” for more details), and we eagerly awaited the publication of this important manuscript.

What on earth are you laughing about? These experts have vast knowledge of great tits (Parus major), blue tits (Parus caeruleus), willow tits (P. montanus), and many other hole-nesting passerine bird species found throughout the Mediterranean. While data are available on populations of marine birds that extend for centuries and more, Grosbois et al. state “To our knowledge, such lengthy indirect indices are not available for land birds.” However, “Several hole-nesting passerine birds such as tits and flycatchers have been subjected to long-term monitoring programmes in several populations scattered over their distribution ranges, providing the opportunity to investigate climate impacts at large geographic scales.”

Based on previous studies, population growth rates of great tits, blue tits, and pied flycatchers are impacted significantly by winter and spring climatic conditions. However, many of the prior studies were conducted in the northern part of the species’ ranges, and choosing the more northerly locations may have biased the studies in terms of detecting sensitivity to winter and early spring conditions. The team notes “Furthermore, the authors of some of these studies addressed influences of climatic conditions at other times of year but failed to detect any.” It seems from these previous studies that conditions in the summer are far less important than conditions in winter when it comes to survival and health of the tits.

In this recent study, the tit specialists decided to investigate the survival rates of blue tits in the southern limit of the species range in the Mediterranean basin. From 1985 to 2000, adult blue tits were captured and ringed annually at nest boxes during the nestling feeding period from March to June. Two collection sites were in Corsica and one was in the mainland southern France. In addition to the tit data, they collected monthly records of total rainfall, rainfall days, average minimum temperature, average maximum temperature, mean temperature, strongest wind gust, and the average speed of the wind by direction. They also gathered data on regional and hemispheric teleconnections such as the North Atlantic Oscillation, Sahelian precipitation, the Indian Monsoon, and El Niño/Southern Oscillation.

Grosbois et al. used a series of sophisticated multivariate statistical techniques to link the interannual variation in blue tit adult survival to the climate variables, and they found that the variations in climate could account for 66% to 73% of the variation in survival. The team reports “As expected, adult mortality peaked during winter and was chiefly influenced by winter climatic conditions” and “It could consequently be concluded that an increase in winter temperatures as a result of global warming could result in reduced blue tit mortality.” Terrific, global warming is wonderful for the tits, and the good news is that climate models predict more winter warming than summer warming throughout Europe.

It is quite possible that gains from a warmer winter could be lost if summers heat up, and the heat wave of the summer of 2003 is still fresh in the minds of many Europeans. Generally, Grosbois et al. did not find much of a link between blue tit mortality and summer conditions. The tit team notes “as long as the mechanisms underlying the impact of summer climatic conditions on blue tit survival remain unknown, the phenological, behavioural, morphological, or physiological traits upon which these selective pressures are likely to exert an influence cannot be determined and it is impossible to evaluate whether these unknown traits are likely to evolve under the influence of selective pressures induced by the summer warming trend.” They conclude “because too few studies have so far addressed the influence of summer climate variation on the physiology of passerine birds, the support for this hypothesis can presently not be considered as solid.” The tits of the Mediterranean do not appear to respond to climatic variations during the summer months.

So we find in this article that global warming could result in a more robust tit community in the Mediterranean, at least for the blue tits. Hopefully, these experts will turn their attention to the great tits, as well as other tits, sometime in the future, and if they do, we will gladly focus once again on global warming and the tits throughout the world.

Reference

Grosbois, V., P.-Y. Henry, J. Blondel, P. Perret, J.-D. Lebreton, D.W.Thomas, and M.M . Lambrechts, 2006. Climate impacts on Mediterranean blue tit survival: An investigation across seasons and spatial scales. Global Change Biology,12, 2235–2249.




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