Resting metabolic rate and cost of locomotion in long-term fasting emperor penguins

Abstract

During the Antarctic winter emperor penguins fast for up to 120 days when breeding at rookeries, which may be as much as 120 km from open water. Emperors have lost almost half of their body mass by the time they walk back to the sea to feed. Resting metabolic rate and metabolic rate during treadmill walking at 1.4 km times h-1 were measured regularly along the course of 63-118 days of fasting in four emperors that lost between 33 and 55% of their body mass. Resting metabolic rate decreased linearly with body mass throughout the fast; it was 76 and 50 W at 39 and 18 kg body mass, respectively, which therefore corresponds to a limited increase in the resting metabolic rate per unit of body mass. There was a considerable decrease in the metabolic rate for walking at 1.4 km times h-1, from 340 to 140 W at body masses of 39 and 18 kg, respectively; this decrease was linear with body mass but at a steeper rate below 23 kg. From 39 to 23 kg, the cost of walking per unit of body mass remained constant. Below 23 kg (a point where about 2.5 kg of fat remain), the increased efficiency for walking may be due to a change in the mechanics of locomotion.

Energy saving processes in huddling emperor penguins: from experiments to theory

“…We estimated that a major part of energy savings for Maho et al, 1976;Pinshow et al, 1976;Dewasmes et al, 1980;Gilbert et al ., 2007).…”

“…Reported mean stomach temperatures of isolated birds measured during respirometry studies in the laboratory were 37.8°C (Pinshow et al, 1976), 38.2°C (Le Maho et al, 1976 and 39.4°C (Dewasmes et al, 1980). As expected, the measured mass-specific metabolic rate (measured at rest, within the TNZ) of emperor penguins was positively correlated with stomach temperature: 1.83·W·kg -1 (Pinshow et al, 1976), 1.98·W·kg -1 (Le Maho et al, 1976) and 2.32·W·kg -1 (Dewasmes et al, 1980), accounting for body mass differences, which were small: 23.4·kg (Pinshow et al, 1976), 24.8·kg (Le Maho et al, 1976 and 25.0·kg (Dewasmes et al, 1980). Dewasmes et al discussed the link between the decrease in metabolic rate and body temperature decline, since mean stomach temperature in their birds ranged from 38.5°C to 40.0°C (Dewasmes et al, 1980).…”

Metabolism and thermoregulation during fasting in king penguins,Aptenodytes patagonicus,in air and water

“…Interspecific allometric mass exponents for resting metabolic rate in air range from 0.66 to 0.92 (14,38), but intraspecific mass exponents Ͼ1 have been reported in fasting birds (13,16,17,27). Thus there is little reason to assume a direct relationship on a mass-specific basis within and between species.…”

What triggers the aerobic dive limit? Patterns of muscle oxygen depletion during dives of emperor penguins

“…This mean value is approximately one-third of both the field metabolic rate measured at the isolated dive hole with doubly labeled water and the lowest rate measured in penguins swimming in a flume (20 and 20.7ml O 2 kg -1 min -1 , respectively) (Kooyman and Ponganis, 1994;Nagy et al, 2001). It is equivalent to resting metabolic rate measured in emperor penguins floating in a flume (6.2-6.7ml O 2 kg -1 min -1 ) (Kooyman and Ponganis, 1994) or standing in their thermoneutral zone (Dewasmes et al, 1980;LeMaho et al, 1976;Pinshow et al, 1976). This mean O 2 consumption is also slightly greater than the resting rate predicted by allometric equations relating metabolic rate to body mass (Aschoff and Pohl, 1970).…”