FIELD ENERGY EXPENDITURES OF THE SOUTHERN GIANT-PETREL

We used the doubly labeled water method to measure rates of energy expenditure in free-living Southern Giant-Petrels (Macronectes giganteus, mean body mass = 3.89 kg) at Palmer Station, Antarctica. Despite superficial morphological and behavioral resemblances to the energetically efficient albatrosses, giant-petrels have high energetic costs while foraging, averaging 6.3 x SMR (standard metabolic rate), which is much higher than the values for three Diomedea albatrosses (1.8 to 2.7 x SMR). The integrated field metabolic rate (FMR, incorporating time spent foraging and brooding) of a giant-petrel is 4,270 +/- 668 kJ day-1, the highest absolute value yet measured in any bird. Their overall FMR is 4.6 x SMR, slightly higher than the suggested upper limit of 4.0 x SMR for breeding birds. Compared with similar-sized albatrosses, Southern Giant-Petrels are more heavily wing-loaded, they flap more frequently, and they deliver meals more frequently to their chicks. These factors probably contribute to their higher rates of energy expenditure. Giant-petrels breed most abundantly at high latitudes, outside the breeding range of albatrosses. An energy-expensive breeding strategy that incorporates relatively rapid nestling growth and high rates of chick-feeding by adults may account for the success of Southern Giant-Petrels in the short growing season Antarctic habitat.