UNDERWATER SWIMMING AT LOW ENERGETIC COST BY PYGOSCELID PENGUINS

Energetic requirements of under-water swimming in pygoscelid penguins were studied in Antarctica, using respirometry together with a 21m lon g swim canal and externally attached devices recording the swimming sp eed and dive duration of unrestrained animals. Field measurements were compared with measurements of the hydrodynamic properties of an Adeli e penguin model in a circulating water tank. Minimium transport costs during underwater swimming in Adelie (Pygoscelis adeliae), chinstrap ( P. antarctica) and gentoo (P. papua) penguins averaged 4.9, 3.7 and 7. 6Jkg(-1)m(-1) respectively, at their preferred swimming speeds of 2.2, 2.4 and 1.8 ms(-1), allowing the birds to dive aerobically for 110, 1 30 and 93s, respectively. From the swim canal measurements, we calcula ted a drag coefficient (C-D) of 0.0368 for a typical Adelie penguin at 2.2ms(-1). This value is significantly lower than the C-D of 0.04 of an ideal spindle and the C-D of 0.0496 measured on the model in the la boratory. The reasons for this difference are discussed.