Fig. 5. (A) Heart rate (f_H) over a 10 min period in emperor penguin 22 resting on the sea ice. Note the regular, momentary tachycardias. (B) Heart rate (black) and impedance signal (red) from emperor penguin 32 during 1 min at rest. The maxima in the impedance signal were visually verified as corresponding to inspiration (grey squares). The tachycardia associated with each visually confirmed inspiration is associated with the upstroke in the impedance signal. Respiratory rate in this case is counted as 4 breaths min^–1.