Figure 1.

Beat-to-beat heart rate profiles of emperor penguins diving either at an experimental isolated dive hole in McMurdo Sound, Antarctica, or during foraging trips at sea from Cape Washington, Antarctica. Heart rate profiles were characterized by an immediate decline from high pre-dive levels [200–240 beats min⁻¹ (bpm)], a continued gradual decline to below-resting levels over the initial 1 to 2 min, and then a further progressive decline as dive duration increased. In the bottom phase of long dives and deep dives, heart rates could be as low as 5–10 bpm. Ascents were characterized by a gradual increase in heart rate. Heart rate profiles were characterized by abrupt oscillations in heart rate throughout the dive. Heart rate at rest was about 72 bpm. Adapted from the data of Meir et al. (2008) and Wright et al. (2014).