Fig. 4. Relationship between measured speed (thick black line) and simulated speed (colored dots and lines) during the passive ascent periods of a king penguin (A) and an Adélie penguin (B). Values beside the lines are air volume (1) that might be kept by birds ascending passively (1 atm) used in the model simulation. Measured decompression ratio and ascent angles are shown as thick black lines. Simulated decompression ratios and lift coefficients are also shown (colored dots and lines), assuming that each bird had 1.2 (A) or 0.9 litres (B) of air (1 atm). The depths at which the birds stopped flipper beating are indicated.