PREDATION ON BURROWING PETRELS BY THE BROWN SKUA (CATHARACTA-SKUA LONNBERGI) AT MAYES ISLAND, KERGUELEN

The diet of the brown skua (Catharacta skua lonnbergi) was studied at Mayes Island, Kerguelen archipelago, by collection of prey remains on II territories during the complete breeding cycle of the species there . In nine territories, collections were daily or every two days for a quantitative investigation of the diet. The blue petrel (Halobaena cae rulea) and thin-billed prion (Pachyptila belcheri) accounted for, resp ectively, 72.9 and 19% of the remains. Differences in diet and prey ca pture rate were analysed according to territory size, local abundance of prey inferred from the vegetation cover of territories, colony atte ndance patterns of prey, and according to the breeding timing and succ ess of skuas. Skuas holding large territories caught more prey, and es pecially more blue petrels than those with small territories. Diet ref lected local abundance of blue petrel and thin-billed prion but the bl ue petrel was apparently preferred to other available prey. Failure to breed was not significantly related to hunting performance of the sku a or to food availability, but sample size was small. Variations over time of prey capture rates reflected the colony attendance patterns of the main prey. Captures of blue petrel and thin-billed prion were mos t numerous during their respective laying, incubation and hatching per iods, decreasing during chick-rearing. Prey capture rates were greates t when brown skuas were hatching, and decreased during chick-rearing t o a minimum when young skuas were fledged. Capture rate patterns diffe red according to laying date of skuas: early breeding skuas caught mor e prey and were well synchronized with the breeding cycle of the blue petrel and late breeders exhibited more dependence on the thin-billed prion for some periods. Finally, this study has allowed us to assess t he impact of the brown skuas upon the burrowing petrels on this locali ty.