Fig. 9. Power input (energy expended per second) for a swimming Magellanic penguin as a function of drag. This was derived by using a polynomial fit for the mass-specific power requirements as a function of swim speed for Humboldt penguins given by Luna-Jorquera and Culik (2000) (Equation 9 in text) and then regressing these power-requirements against the drag experienced by the penguins swimming at the corresponding speed. The drag–speed relationship was determined from the standard formula (Equation 10 in text), which incorporates a drag coefficient of 0.03 (Bannasch, 1995) and a cross-sectional area of 0.018m² (see text).