Seabird reproduction in an unpredictable environment: how King penguins provide their young chicks with food

Pelagic seabirds depend on resources far out at sea and for which the availability can vary greatly. King penguins rely essentially on myctophid fish, which in summer are mostly available 400 to 500 km south of the Crozet Archipelago at the Antarctic Polar Front. Incubating male King penguins anticipate a possible delay in the return of the female by storing food in their stomach for several weeks, which enables them to feed the chick quickly if hatching occurs. We investigated the foraging trip duration, adult body mass regulation and the meal size for chicks relative to the laying date and the Polar Front position. We compared, in both early and late breeders, the energy content and the chemical and diet composition of the meals stored in their stomachs. During food storage by the male, the cessation of digestive processes was not complete as the meal showed some modifications of the biochemical composition, especially a decrease in lipid content; this is in contrast to oil storage in albatrosses and petrels, in which there is an increase in lipid content. On average, females came back from their second foraging trip at sea a short time before hatching. However, the trip durations were particularly variable depending on date and year, and as a consequence hatching occurred with either the female or the male incubating the egg. Late breeders showed longer foraging trip duration and built up larger fuel reserves than early breeders. Their energetic output per day foraging at sea was much lower than for early breeders. These differences in foraging trip durations of males were linked to a change in marine resource availability because, in spite of being at the same stage of the breeding cycle, male late breeders caught different prey compared to male early breeders. We assume that this strategy of long-term food storage and conservation in the stomach while fasting evolved in response to the unpredictable variations of water mass positions.