Interannual dietary changes and demographic consequences in breeding blue petrels from Kerguelen Islands
Résumé
Interannual variation in summer diet and demographic parameters of blue petrel Halobaena caerulea were investigated to understand how changes in the marine environment affect the reproduction of an oceanic seabird from the Southern Ocean. Lipids from stomach oil were used as trophic markers of prey consumed by adult birds when they self-fed during long trips, and conventional food analyses allowed determination of the food delivered to chicks after long and short adult foraging trips. Biochemical analysis of stomach oil showed little differences in lipid classes and in fatty acid and fatty alcohol compositions, with most oils deriving from triacylglycerol- and wax esterrich myctophid fishes over the 4 yr study period (1996, 2000, 2001 and 2002). Accordingly, stomach content analysis showed that chick food was dominated by mass by crustaceans and fish, with myctophids as the main fish items. Important interannual variations in chick diet occurred, most prominently featuring an almost lack of fish in 2002. Summer 2002 was also marked by the lowest fledging success, lowest mass of chicks at fledging and lowest summer survival of adults during the period 1986–2002. In contrast to 1996, 2000 and 2001, summer months in 2002 were also characterized by an intense warm event in Kerguelen waters. Overall, results strongly suggest causal links between climatic anomalies, availability of myctophids and dietary shifts with poor reproductive performance and lower survival in blue petrel. Furthermore, they emphasize the importance of lipid-rich prey in seabird nutrition.
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