Ecology and Physiology of Fasting in King Penguin Chicks

Abstract Captive King Penguin (Aptenodytes patagonica) chicks can fast for 5 months during the subantarctic winter with a 70% decrease in body mass. To investigate the adaptive value of this remarkable resistance to starvation, we compared captive chicks with free-ranging chicks in their colony at Possession Island, Crozet Archipelago. The chicks in the colony, from mid-April to beginning of September (i.e. all winter) were fed only every 39 days by their parents; some were not fed at all. In spring (October-December) the surviving chicks were fed every 6 days, and their growth was completed. Overall chick mortality in the colony during the winter and subsequent spring was about 50%. Mortality was highest in October, 6 months after the beginning of the winter, and may be attributed mainly to starvation. The decrease in body mass in the free-ranging chicks was remarkably similar to that for captive birds. In both groups, three periods were characterized according to the observed changes in the daily decrease in body mass per unit body mass (dm/mdt): dm/mdt dropped during the first period (I) of 5-6 days, was minimum and steady during period II, which lasted about 4 months, and increased in period III. Blood analysis of the captive chicks indicated the three periods correspond to modifications in protein breakdown. An initial decrease in uricacidemia indicates period I is a short period of transition, marked by a decrease in protein breakdown. In period II a minimum and constant uricacidemia, in parallel with a progressive increase in ketonemia, indicates efficient protein sparing while most of the energy is derived from lipids. Period III is critical because, from a rise in uricacidemia concomitant with a decreasing ketonemia, proteins are no longer spared. The extreme resistance of King Penguin chicks to starvation in winter may be explained partly by the ability to spare proteins for several months (period II). It occurs at a growth stage when the parents' feeding visits are rare. Other laboratory and field investigations of birds suggest that the means by which a wide variety of domestic and wild species adapt to fasting also may be interpreted in terms of three periods corresponding to changes in protein breakdown.