Energy costs of incubation and moult in petrels and penguins
Most penguins and petrels fast during lengthy incubation shifts; all penguins fast through their moult. The resulting weight losses can be used to calculate energy costs of these activities and to examine relationships between body weight and energy consumption. (2) Field data for thirteen species of petrel (albatrosses to storm-petrels) and fourteen (of seventeen) species of penguin are reviewed and oxygen consumption data for seven penguins are summarized. (3) For incubating and moulting birds the log-log relationships between energy consumption (kcal day-1) and body weight have slopes of 0.67-0.77, close to that of non-passerines generally (0.73). The slope for oxygen consumption data (0.74) is very similar. These data also support the present assumption that only about half the material lost during these fasts is fat, the rest being mainly water. Proportionate weight loss (g g-1 day-1) during fasting is approximately proportional to body weight (g) to the power of -0.27, as can be predicted theoretically. (4) The daily energy cost of incubation in petrels and penguins is about 1.3-1.4 times the estimated cost of basal metabolism. Daily moult costs in penguins are about twice basal metabolism.