Figure 3.
Emperor penguins diving at an isolated dive hole make routine dives of 5–6 min duration, near the 5.6 min measured aerobic dive limit (ADL, dive duration associated with the onset of post-dive blood lactate concentration) [109]. Biologging investigations of such dives have revealed (a) a moderate bradycardia (decline in heart rate) and predominantly low stroke rates, (b) conservation of core temperatures and cooling of the periphery, (c) compression hyperoxia and then a gradual, but incomplete decline in the partial pressures of oxygen (PO2) in air sacs and blood, and (d) incomplete arterial and venous haemoglobin desaturation but near complete depletion of the myoglobin-bound oxygen store in muscle. These findings support the concept that the ADL is secondary to depletion of the muscle oxygen store and subsequent glycolysis in muscle. The illustrated profiles in (a) are from the same dive; data profiles in the other figures are from individual dives of about 6 min duration in different birds. Adapted from [36,64,68,76,78,82,111,112].