Abstract: In: Encyclopedia of Islands
(eds. Gillespie R.G. & Clague D.A.), University of California Press, Berkeley

Abstract: King penguin chicks, that are strictly terrestrial during first year after hatching, must depart to sea to reach nutritional emancipation. Juvenile survival therefore depends on their adaptation to the energetic challenges of marine life: 1) harsh thermal environment, 2) long distant food resources, 3) repeated, deep and prolonged nutritional divings.
To elucidate these adaptations, the transcriptome of pectoralis muscle, the main thermogenic and locomotor tissue, was analysed in juveniles that had never been to sea (n=4) and in naturally adapted juveniles (n=3) by using chicken Affymetrix DNA chips (Profilexpert, Lyon).
Results showed the differential expression of nearly 3600 genes after marine life. Genes encoding enzymes of carbohydrate metabolism were down regulated while those encoding lipid transport and catabolism were up regulated suggesting an increased use of lipids as energy substrates. Further, transcripts encoding enzymes involved in cellular defense against reactive oxygen species and the associated injuries were also up regulated, suggesting an adaptive response against oxidative stress.
This study opens large perspectives to elucidate how king penguins can survive in an energetically unfavorable and pro-oxidative environment and what contributes to their remarkable longevity.
This study received the financial support of the French Polar Institut (IPEV).

Abstract: In seabirds, variations in stress hormone (corticosterone; henceforth CORT) levels have been shown to reflect changing marine conditions and, especially, changes in food availability. However, it remains unclear how CORT levels can be mechanistically affected by these changes at the individual level. Specifically, the influence of food acquisition and foraging success on CORT secretion is poorly understood. In this study, we tested whether food acquisition can reduce baseline CORT levels (;the food intake hypothesis') by experimentally reducing foraging success of King Penguins (Aptenodytes patagonicus). Although CORT levels overall decreased during a foraging trip, CORT levels did not differ between experimental birds and controls. These results demonstrate that mass gain at sea is not involved in changes in baseline CORT levels in this species. The overall decrease in CORT levels during a foraging trip could result from CORT-mediated energy regulation (;the energy utilisation hypothesis'). Along with other evidence, we suggest that the influence of foraging success and food intake on CORT levels is complex and that the ecological meaning of baseline CORT levels can definitely vary between species and ecological contexts. Therefore, further studies are needed to better understand (1) how baseline CORT levels are functionally regulated according to energetic status and energetic demands and (2) to what extent CORT can be used to aid in the conservation of seabird populations.

Abstract: Aquatic endotherms living in polar regions are faced with a multitude of challenges, including low air and water temperatures and low illumination, especially in winter. Like other endotherms from cold environments, Great Cormorants (Phalacrocorax carbo) living in Arctic waters were hypothesized to respond to these challenges through a combination of high daily rate of energy expenditure (DEE) and high food requirements, which are met by a high rate of catch per unit effort (CPUE). CPUE has previously been shown in Great Cormorants to be the highest of any diving bird. In the present study, we tested this hypothesis by making the first measurements of DEE and foraging activity of Arctic-dwelling Great Cormorants throughout the annual cycle. We demonstrate that, in fact, Great Cormorants have surprisingly low rates of DEE. This low DEE is attributed primarily to very low levels of foraging activity, particularly during winter, when the cormorants spent only 2% of their day submerged. Such a low level of fo...