The non-breeding season of seabirds is extremely challenging to study because it is often spent offshore under harsh environmental conditions. We used stable isotope analysis to investigate little auk Alle alle feeding ecology throughout the annual cycle. The geographic distribution of little auks in the Arctic covers a wide range of oceanographic conditions. We sampled birds from 5 different colonies located in the most important breeding areas (Greenland and Spitsbergen) to examine how individuals breeding in contrasting marine environments differ in their trophic niche throughout the year. We found differences in summer δ15N values among the colonies, suggesting different target species despite low overall δ15N values in blood, which indicates a diet that is primarily composed of copepods. A rise in δ15N values between summer and autumn indicated that adults changed their trophic status to feed at a higher trophic level. During autumn, a large overlap in feather 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 Spitsbergen birds 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 contrasting seasonal and regional diet in little auk populations, and reveal possible population overlaps during the autumn moult. We found substantial trophic variability in little auks, which may indicate unsuspected capabilities to adapt to current, drastic environmental change in the North Atlantic.