Diet and feeding ecology of blue petrels Halobaena caerulea at Iles Kerguelen, Southern Indian Ocean
Résumé
The food and feeding ecology of the blue petrel Halobaena caerulea was investigated over 4 consecutive chick-rearing periods at Iles Kerguelen. In all years, blue petrels fed on a large diversity of crustaceans and fish, with a small proportion of squid and other organisms. Crustaceans ranked first by number (98%) and second by reconstituted mass (37%). The hyperiid Themisto gaudichaudii and the euphausiid Thysanoessa sp. were the dominant prey items, accounting each for 42% by number, and for 12 and 4% by mass of the diet, respectively. Other important crustacean prey were the Antarctic krill Euphausia superba (2% by number and 10% by mass) and the large shrimp Pasiphaea scotiae (<1 and 5%, respectively). Fish were minor items by number (<1%) but, owing to their large size, they dominated the diet by reconstituted mass (57%). Mesopelagic fish of the families Myctophidae (14% by mass) and Melamphaidae (12%) were the main fish prey together with the gempylid Paradiplospinus gracilis (19%). Adult blue petrels use a 2-fold foraging strategy, performing short trips (ST, 2 d on average) and long trips (LT, 7 d) during the chick-rearing period. Birds fed more on T. gaudichaudii during ST and more on Thysanoessa sp. during LT. The subantarctic krill Euphausia vallentini were found in ST samples, and Antarctic krill and stomach oil were found in LT samples. Biogeography of the prey shows that blue petrels fed in a wide variety of marine habitats. During ST, they foraged in the kelp belt and over the shelf, but favoured oceanic waters in the vicinity of the archipelago. During LT, the occurrence of Antarctic krill indicates feeding in southern Antarctic waters, >1000 km from the breeding colonies, but blue petrels also foraged on their way back to Iles Kerguelen from these distant foraging grounds to feed their chicks. A comparison of the stable carbon and nitrogen isotopic compositions of chick and adult feathers reveals that adult blue petrels fed at the same trophic level during the chick-rearing and moulting period, and that they renew their flight feathers in Antarctic waters.