Regulation of energy expenditure in free-living animals under extreme conditions.

Abstract

The Emperor Penguin (Aptenodytes forsteri) reproduces at the borders of the Antarctic continent. Because of the large size of the species, birds require a long period between egg laying and chick independence. Egg laying starts in the middle of the Antarctic winter. Only the males incubate the egg during a period of about 90 days, during which they only can rely on their internal (fat) reserves. After hatching, the females return from the sea to take over the feeding of the small chick. Using stable isotope methodology, measurements were made for the development of body mass, body composition, and energy expenditure. A comparison was made between incubating males while huddling with other males, versus males which were incubating solitarily. The latter males were permanently exposed to the harsh environmental conditions and had to cover high thermoregulatory costs, which resulted in an elevation of the metabolic rate by about 20%. In these birds, the stored fat deposits deminished at a relatively high rate, leading to a high incidence of nest desertion. The Cape Gannet (Morus capensis) is an other seabird species facing extreme and unpredictable feeding conditions. The entire world's population is distributed over six colonies in southern Africa, where they feed on various fish species. The location of the food is rather unpredictable, and related to the level of upwelling of the nutrient-rich Antarctic water. We applied GPS loggers to monitor daily feeding activity, and Doubly Labeled Water to measure energy expenditure in free-ranging birds during the chick-rearing period.