Energetics, growth, and body composition of Adélie penguin chicks, Pygoscelis adeliae

Adélie penguins are very abundant in Antarctica and constitute a large biomass of predatory consumers in the Antarctic ecosystem. Adélies eat almost exclusively krill (Euphausia spp.), and to determine krill requirements by Adélies, information on energetics is needed, including energy intake of the chicks. I measured energy use and growth in Adélie penguin chicks, using both field and laboratory techniques. Field metabolic rate was quite variable, but mass-specific rates were not correlated with body mass. Growth followed the logistic equation: the growth constant was 0.143 d-1, and the asymptote for growth to fledging was 3,200 g. Different body organs had similar energy densities (in kilojoules per gram of dry mass), and total body energy density did not vary with chick mass. However, proportional mass of the skin increased rapidly as chicks grew, making the skin an important energy store in larger chicks. Metabolic efficiency measured in the laboratory averaged 69% and did not vary with chick mass. Total energy ingested over the 50-d development period was 162 MJ, which corresponds to approximately 33.6 kg of fresh krill. Previous studies of Adélie energetics have focused on adult energy balance and have calculated chick energy requirements indirectly on the basis of adults' stomach loads of krill and frequency of feeding chicks. Values from previous studies do not agree with those from the present study. The method used in the present study is more informative and accurate for measuring energy use by chicks, since measurements are made directly from chicks.