| Summary: | International audience The diet of seabirds is usually studied by the identification of prey items recovered from their stomachs. This method is however limited to recently ingested prey and to non-digestible hard parts, precluding the determination of marine resources consumed by birds during long foraging trips. Thus, alternative indirect approaches are necessary to assess the potential importance of digested prey from long-term foraging activity. In this study, we present three complementary techniques to determine the prey of breeding short-tailed shearwaters (Puffinus tenuirostris) when they feed for themselves during long foraging trips: (1) conventional food analysis, (2) stable isotope analysis of carbon and nitrogen signatures (δ13C and δ15N) of plasma, and (3) lipid analysis of stomach oil and the use of fatty acids and fatty alcohols as trophic markers (stomach oil is of dietary origin). Dietary analysis showed that fish dominated by mass over crustaceans (82 and 18%, respectively). Two euphausiids Euphausia vallentini (a sub-Antarctic species) and Nyctiphanes australis (a Tasmanian species), and fish postlarvae represented more than 94% of the total number of food items, with myctophid fish of larger size dominating by mass. Plasma isotopic signature of birds suggested that shearwaters foraged mainly in Antarctic waters (δ13C = -23.8‰), and fed at a trophic level close to that of a myctophid-eater, the king penguin (δ15Nshort-tailed shearwater = 8.7‰, δ15Nking penguin = 9.8‰). Comparisons between fatty -acid and -alcohol patterns of stomach oil wax esters with those of potential prey also suggested a food based on myctophids (Electrona antarctica, Krefftichthys anderssoni and Gymnoscopelus braueri). To conclude, both lipid and stable isotope methods emphasized the importance of myctophids in the nutrition of short-tailed shearwaters during the chick-rearing period when adult birds feed for themselves. This study illustrates the interest of using both direct and indirect methods to determine trophic ...
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