Trees, Caterpillars, Birds and Climate
Bauer, Z., Trnka, M., Bauerova, J., Mozny, M., Stepanek, P., Bartosova, L. and Zalud, Z. 2010. Changing climate and the phenological response of great tit and collared flycatcher populations in floodplain forest ecosystems in Central Europe. International Journal of Biometeorology 54: 99-111.
In a study designed to answer this question for certain elements of an important ecosystem of Central Europe, Bauer et al. (2010) studied the responses to 47 years of warming (1961-2007) of (1) the time of leafing-out of dominant English Oak (Quercus robur) trees at four different research sites in the Czech Republic that are located in full-grown, multi-aged floodplain forests that had been under no forestry management, (2) the time of appearance of the two most abundant species of caterpillars in the floodplain forests -- the Winter Moth (Operophtera brumata) and the Tortrix Moth (Tortrix viridana) -- and (3) the first and mean laying dates of two of the ecosystem's most common birds: Great Tits (Parus major) and Collared Flycatchers (Ficedula albicollis).
According to the researchers, "mean annual temperature showed a significant increase of 0.27-0.33°C per decade, with approximately the same magnitude of change during spring at all sites." They also found that "on average (all four sites), the bud burst date for English Oak has advanced by 7.9 days and full foliage by 8.9 days, with approximately the same shifts being recorded for the peak of the beginning and end of frass for herbivorous caterpillars," which was the observational variable they used to characterize the caterpillars' presence. Last of all, they determined that "the first laying date of Great Tits has advanced by between 6.2 to 8.0 days," while "the mean laying date has advanced by 6.4 to 8.0 days." Likewise, they found that the "Collared Flycatcher first laying date has advanced by 8.5 to 9.2 days over the past 47 years, and the mean laying date by 7.7 to 9.6 days."
With respect to the importance of their findings, the authors state that because "trends in the timing of reproduction processes of both bird species are coherent with the trends in development of English Oak and with peak herbivorous caterpillar activity," it is readily apparent that in this specific food chain the common shifting of the different organisms' phenological stages toward the beginning of the year "does not appear to have led to mistiming in the trophic food chain." Hence, there is reason to believe that other food chains may also not be as seriously disrupted by global warming as many have postulated they could be. Obviously, however, much more work of this nature is needed before any generalities are warranted.
Visser, M.E. and Both, C. 2005. Shifts in phenology due to global climate change: the need for yardstick. Proceedings of the Royal Society B 272: 2561-2569.