Foraging behavior of little auks in a heterogeneous environment

The Atlantic sector of the Arctic is currently undergoing large-scale changes in the distribution of water masses in response to the pronounced positive values of the North Atlantic Oscillation. As a consequence the area surrounding little auk Alle alle colonies on Svalbard has experienced an increase in the inflow of Atlantic water. In this study, the influence of water mass distribution on the foraging ecology of little auks was examined through simultaneous measurements made at colonies in Hornsund Fiord (7703' N, 1510' E) and at sea. In the colony we measured chick diets, while at sea, we assessed the distribution of foraging little auks and the zooplankton available to them within different water masses. Our results indicate that little auks feed mainly on the large copepod Calanus glacialis. They restrict their foraging activity to Arctic water that contains this copepod and avoid Atlantic water that contains a smaller copepod, C. finmarchicus. Little auks breeding on Svalbard may be impacted by climate change because during years when the flow of Atlantic water increases, they may be forced to forage in areas with sub-optimal conditions.