COMPARISON OF BODY RESERVE BUILDUP IN PREFASTING CHICKS AND ADULTS OFKING PENGUINS (APTENODYTES-PATAGONICUS)

Like other penguin species, adult king penguins (Aptenodytes patagonic us) fast several weeks when they molt and at the beginning of their br eeding cycle. Moreover, chicks of this species can withstand up to 5 m o of food deprivation during the austral winter. To assess possible va riation in the prefasting amounts of nutrient reserves, we determined body composition (water, protein, total lipid, and ash contents) of ad ults and chicks of king penguins at the beginning of their long-term f asts. Accumulation of subcutaneous fat stores anticipates each of thes e periods and appears to be an obligatory prerequisite to fasting. How ever, prewinter chicks contained 1 kg more fat and, consequently, bad a higher adiposity (34%) than premolting chicks (22%) and prebreeding adults (18%), indicating that the higher the fat stores, the higher th e fast resistance. Prewinter chicks also possess a 19% lower lean body mass (6.61 vs. 8.12 kg in premolting chicks), that is, a low amount o f metabolically active tissues, thus minimizing their fasting energy e xpenditure. When compared with adult breeding fast, adult molt is anti cipated by a 3.3-kg body mass increase due mainly to water (67%) and p rotein (23%). Two tissues (integument and pectoral muscles) account fo r 84% of this body mass difference. The increase in integument (feathe r, skin, and subdermal fat) mass involves water and fat (59% and 28% o f the mass increase, respectively), whereas that in breast muscle mass involves protein and water (32% and 68% of the increase, respectively ). Such protein stores anticipate the use of endogenous body protein f or new feather synthesis during the molting fast. This study clearly s hows that different amounts of fat and protein are built-up in anticip ation of fasts of different durations and nutrient needs in king pengu ins.