Oxygen consumption (VO2), heart rate and blood chemistry were measured in four emperor penguins, Aptenodytes forsteri (Gray), during graded swimming exercise. The maximum VO2 obtained, 52 ml O2 kg-1 min-1, was 7.8 times the measured resting VO2 of 6.7 ml O2 kg-1 min-1 and 9.1 times the predicted resting VO2. As the swimming effort rose, a linear increase in surface and submerged heart rates (fH) occurred. The highest average maximum surface and submersion heart rates of any bird were 213 and 210 beats min-1, respectively. No increase in plasma lactate concentrations occurred until VO2 was greater than 25 ml O2 kg-1 min-1. At the highest VO2 values measured, plasma lactate concentration reached 9.4 mmol l-1. In comparison with other animals of approximately the same mass, the aerobic capacity of the emperor penguin is less than those of the emu and dog but about the same as those of the seal, sea lion and domestic goat. For aquatic animals, a low aerobic capacity seems to be consistent with the needs of parsimonious oxygen utilization while breath-holding.

This content is only available via PDF.