Abstract
This chapter presents a study on the body energy level in fasting-refeeding in the emperor penguin. During breeding, male and female emperor penguins fast for 45 and 110 days, respectively, on sea-ice. In this study, body mass (BM) was determined in free-living birds leaving the rookery to feed in sea at the end of fasting. Mean BM was 23 kg and, therefore, birds had about 2 kg of fat left and were still in the first phase of fasting. However, for most of these birds, the signal for fasting end had been behavioral. The lower BM was 20.45 kg in both sexes. It was concluded that the lower BM of birds leaving to feed in sea is identical to the critical BM. Because the birds with this lower BM were probably those who spontaneously stopped fasting, these results are strongly indicative that the activation of body protein degradation and/or the fat store exhaustion is the physiological factor that triggers refeeding in free-living penguins. The observation that the fat-free body mass (protein) reconstituted before the fat mass during refeeding could suggest that this physiological signal is mainly related with the body protein level and/or rate of catabolism.
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