Abstract: 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 delta N-15 values among the colonies, suggesting different target species despite low overall delta N-15 values in blood, which indicates a diet that is primarily composed of copepods. A rise in delta N-15 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 delta C-13 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.

Abstract: King penguins Aptenodytes patagonicus are known to change their diving behaviour in
response to changes in both prey location and their breeding status through the early stages of the
breeding cycle (austral summer and autumn). However, little information exists on whether and how
these changes affect the energy expenditure of such behaviour. By deploying heart rate and hydrostatic pressure data loggers, we investigated detailed changes in the dive time budgeting of king penguins during foraging dives across the breeding season, in the same individuals, and the associated changes in estimated oxygen consumption during those dives. Maximum dive depth, duration,
bottom duration, feeding events (indicated by wiggles) per dive and post-dive duration increased
through the study period. While a foraging dive later in the breeding season was energetically more
costly than a dive earlier in the season, the overall rate of energy expenditure did not change, nor did energy cost per unit prey capture. These findings indicate an ability of king penguins to adjust their foraging dive behaviours through the summer and autumn without affecting the energetic costs of diving to capture prey. Such plasticity may be necessary to compensate for changes both in prey location and abundance, and in the energy requirements of the chick over time.