Fig. 3. Mean heart rate (fH, A), rate of oxygen of consumption (_O2, B) and mass-specific _O2 (s_O2, C) of 22 king penguins walking at different speeds on a treadmill. The birds are in four groups, females (squares, N=5, FD) and males (circles, N=5, MD) departing from the colony and females (triangles, N=6, FA) and males (crosses, N=6, MA) arriving at the colony after a foraging shift. The vertical and horizontal lines at each point represent ± S.E.M.