Food Demand and Availability for a Bird of Northern Finland

Many people worry that global warming may lead to mismatches between the times when birds of temperate and boreal regions require an abundance of food to feed their new hatchlings and the times when that food is available in its greatest abundance; and there have been examples of just such a problem, as in the cases of great tits, blue tits and pied flycatchers in the Netherlands, which require a timely abundance of caterpillars to feed their young (Visser et al., 1998; Visser et al., 2006; Both et al., 2009). However, as Vatka et al. (2011) note, "the same has not happened with great tits in England (Cresswell and McCleery, 2003) nor with great tits and collared flycatchers in the Czech Republic (Bauer et al., 2010)," and they go on to describe yet a third type of food supply-and-demand response to warming that they recently observed and documented.

Working with data collected in northern Finland over the period 1975-2009 within coniferous, deciduous and mixed forests of varying ages -- including young stands, swamps and clear cuttings -- the three Finnish scientists studied "changes in the timing of breeding in the willow tit (Poecile montanus), and timing of its caterpillar food resource in relation to warming springs," using "generalized linear mixed effect models to study the importance of synchrony between the timing of breeding in willow tits and the caterpillar food availability on the breeding success, measured as nestling survival rate and mean nestling weight."

In contrast to prior no change results and poorer synchrony findings, Vatka et al. report that they not only "found no signs of emerging asynchrony," but that they found that synchrony actually improved during the study, and that it had moderate positive effects on breeding success, adding that the observed change in better synchrony mirrors results from the coal tit in the Netherlands, citing the work of Both et al. (2009).

Clearly, all bird species would not be "losers," in terms of food supply-and-demand for their hatchlings, if global warming were to begin again after its recent several-year hiatus. Many species would likely not be affected at all, in fact, while others may even be benefited by such a climate change.

Additional References
Bauer, Z., Trnka, M., Bauerova, J., Mozny, M., Stpanek, P., Bartosova, L. Alud, 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.

Both, C., van Asch, M., Bijlsma, R.G., van den Burg, A.B. and Visser, M.E. 2009. Climate change and unequal phenological changes across four trophic levels: constraints or adaptations? Journal of Animal Ecology 78: 73-83.

Cresswell, W. and McCleery, R. 2003. How great tits maintain synchronization of their hatch date with food supply in response to long-term variability in temperature. Journal of Animal Ecology 72: 356-366.

Visser, M.E., Holleman, L.J.M. and Gienapp, P. 2006. Shifts in caterpillar biomass phenology due to climate change and its impact on the breeding biology of an insectivorous bird. Oecologia 147: 164-172.

Visser, M.E., van Noordwijk, A.J., Tinbergen, J.M. and Lessells, C.M. 1998. Warmer springs lead to mistimed reproduction in great tits (Parus major). Proceedings of the Royal Society of London, Series B 265: 1867-1870.