Many species of large bird fly together in formation, perhaps because flight power demands and energy expenditure can be reduced when the birds fly at an optimal spacing, or because orientation is improved by communication within groups. We have measured heart rates as an estimate of energy expenditure in imprinted great white pelicans (Pelecanus onocrotalus) trained to fly in 'V' formation, and show that these birds save a significant amount of energy by flying in formation. This advantage is probably a principal reason for the evolution of flight formation in large birds that migrate in groups.

We investigated the use of Antarctic waters by king penguins in a 2 yr study based on the satellite tracking of 10 penguins from the Crozet Islands (SW Indian Ocean). All the penguins travelled towards the pack ice, with 3 of them ending their journey at the edge between the marginal ice and the dense pack ice. The mean maximum foraging range and minimal distance travelled were 1620 and 4095 km, respectively. The effect of the satellite transmitter (PTT) attachment on foraging trip duration and colony attendance was much more important in winter in comparison to the summer. The penguins spent around 24% of their trip at sea in the marginal ice zone. They explored the ice-covered habitat non-randomly as revealed by compositional analysis. The marginal ice was more used than free ice and floes areas. The strategy of travelling towards the marginal ice zone during winter ensures that the penguins have access to predictable feeding areas at a time when food availability is very low in the polar frontal zone. The diet of king penguins when foraging in Antarctic waters is unknown but may be different to their summer food at the Polar Front. KEY WORDS: Feeding ecology · Satellite tracking · King penguins · Marginal ice zoneResale or republication not permitted without written consent of the publisher

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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.