Behavioural and physiological significance of minimum resting metabolic rate in king penguins

International audienceSince fasting king penguins (Aptenodytes patagonicus) need to conserve energy, it is possible that they exhibit particularly low metabolic rates during periods of rest. We investigated the behavioural and physiological aspects of periods of minimum metabolic rate in king penguins under different circumstances. Heart rate (fH) measurements were recorded to estimate rate of oxygen consumption during periods of rest. Furthermore, apparent respiratory sinus arrhythmia (RSA) was calculated from the fH data to determine probable breathing frequency in resting penguins. The most pertinent results were: minimum fH achieved (over five minutes) was higher during respirometry experiments in air than during periods ashore in the field; minimum fH during respirometry experiments on water was similar to that while at sea; RSA was apparent in many of the fH traces during periods of minimum fH and provides accurate estimates of breathing rates of king penguins resting in specific situations in the field. Inferences made from the results include: king penguins do not have the capacity to reduce their metabolism to a particularly low level on land; however they can achieve surprisingly low metabolic rates at sea while resting in cold water; during respirometry experiments king penguins are stressed to some degree, exhibiting an elevated metabolism even when resting