Abstract
Climate models predict a multi-degree warming of the North Atlantic in the 21st century. A research priority is to understand the effect of such changes upon marine organisms. With 40 to 80 million individuals, planktivorous little auks Alle alle are an essential component of pelagic food webs in this region that is potentially highly susceptible to climatic effects. Using an integrative study of their behaviour, physiology and fitness at 3 study sites, we evaluated the effect of ocean warming on little auks across the Greenland Sea in 2005 to 2007. Contrary to our hypothesis, the birds responded to a wide range of sea surface temperatures via plasticity of their foraging behaviour, allowing them to maintain their fitness levels. Predicted effects of climate change are significantly attenuated by such plasticity, confounding attempts to forecast future effects of climate change using envelope models.