Résumé
The non-breeding season of seabirds is extremely challenging to study because it isoften spent offshore under harsh environmental conditions. We used stable isotope analysis to investigatelittle auk Alle alle feeding ecology throughout the annual cycle. The geographic distribution oflittle auks in the Arctic covers a wide range of oceanographic conditions. We sampled birds from 5different colonies located in the most important breeding areas (Greenland and Spitsbergen) toexamine how individuals breeding in contrasting marine environments differ in their trophic nichethroughout the year. We found differences in summer δ15N values among the colonies, suggestingdifferent target species despite low overall δ15N values in blood, which indicates a diet that is primarilycomposed of copepods. A rise in δ15N values between summer and autumn indicated that adultschanged their trophic status to feed at a higher trophic level. During autumn, a large overlap infeather δ13C values between colonies suggests a common moulting area off Northeast Greenland.During winter, the isotopic signatures show that the trophic status of Greenland and Spitsbergenbirds differed, with birds from Greenland feeding at low trophic levels (probably mostly on copepods),and birds from Spitsbergen maintaining a higher trophic level. These findings highlight contrastingseasonal and regional diet in little auk populations, and reveal possible population overlapsduring the autumn moult. We found substantial trophic variability in little auks, which may indicateunsuspected capabilities to adapt to current, drastic environmental change in the North Atlantic.