THE EFFECT OF RATION SIZE AND BODY-SIZE ON SPECIFIC DYNAMIC ACTION IN ADELIE PENGUIN CHICKS, PYGOSCELIS-ADELIAE

Specific dynamic action (SDA), also termed the heat increment of feeding, is defined as the postprandial increase in oxygen consumption. The physiological cause of SDA is poorly understood, but most studies point to energetic expenditures associated with protein synthesis Although SDA has been quantified in many different animal taxa, it has seldom been measured in birds. The purpose of this study is to measure SDA in Adelie penguin chicks and to examine possible changes in SDA parameters during growth. Adelie penguin chicks of all sizes exhibited substantial SDA that increased with the size of the meal. The SDA coefficient was 10.0% of ingested energy and 14.8% of metabolizable energy. These values did not vary with body mass. Postprandial peak oxygen consumption rates did not vary with meal size. The time course of SDA increased with the ration level but did not vary with either body mass or meal size alone. Our estimate of the cost of growth in penguin chicks is intermediate between costs measured for other organisms. Specific dynamic action may serve a functional role in thermoregulation for Adelie penguins, which routinely experience temperatures below thermoneutrality. Cumulative SDA during growth is equal to about 62% of the energy deposited in new tissue.