P. Robin. Refeeding signal in fastingincubating king penguins: changes in behavior and egg temperature. Am J Physiol Regulatory Integrative Comp Physiol 279: R2104-R2112, 2000.-This study is directed toward understanding the process of feeding stimulation ("refeeding signal") that has been suggested to operate below a body mass threshold or critical metabolic status in spontaneously fasting birds. Behavior and egg temperature (T egg ) were continuously monitored by video monitoring and

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... try, respectively, in fasting-incubating king penguins kept in a pen to prevent relief by the partner until spontaneous egg abandonment. Penned birds fasted 10 days more and lost 1.2 kg more than birds relieved normally by their partner, abandoning the egg about 1 wk after reaching a critical body mass. Definitive egg abandonment was preceded by transitory abandonments of progressively increasing duration during which time the birds went further and further away from their egg. There were marked interindividual differences but on average transitory abandonments began 36 Ϯ 5 h before the definitive abandonment and were paralleled by resumption of display songs signaling the readiness of the bird to depart for feeding. T egg was maintained at around 35.7°C during normal incubation but significantly decreased the last 2 days before egg abandonment. These changes are interpreted as reflecting a stimulation to refeed at a threshold body mass corresponding to a critical fat store depletion. Thus the fasting-incubating king penguin appears to be an interesting animal model for understanding the long-term metabolic control of feeding behavior in relation to energy status. feeding behavior; spontaneous fasting; incubation; fat stores; body mass threshold; birds ENERGY EXPENDITURE AND ENERGY intake are the two components of the long-term regulation of body mass and principally of body fat. There is evidence that this regulation occurs mainly through the control of energy (food) intake (18, 30, 36) . The control of food intake is at least partly based on metabolic signals for control of eating behavior (5, 7, 14, 16, 32) . Indeed, for changes in energy stores to affect energy intake there must be a mechanism that translates alterations in energy metabolism into this behavior (14). The control of feeding behavior has been investigated mainly in laboratory mammals, which mostly furnishes information on the short-term control, for example meal onset and termination (19, 23, 25). Thus whereas a clear picture of this short-term control is progressively emerging, the longterm metabolic control of feeding behavior is still obscure (21). A better understanding may come from consideration of the behavioral ecology of wild animals, including their reproductive (4) and feeding strategies. Notably, relevant information can be obtained from wild mammals and birds that show prolonged periods of spontaneous hyperphagia and fasting throughout their annual cycle (24). Recent findings suggest that some seabirds breeding in the antarctic and subantarctic regions, e.g., penguins and petrels, can be valuable animal models for studies in this field (9, 17, 22, 28) . Because egg incubation on land competes with feeding at sea, these birds fast ashore for prolonged periods of up to 1 mo or more, relying on large fat stores as the main energy source (17). Parents alternate in incubating and depart to sea for refeeding after relief by the partner. However, the latter can be delayed, forcing the incubating bird to prolong its fast until eventually it abandons its egg and goes to sea for feeding (2, 9) . This finding is in agreement with the previous observation that spontaneously fasting seabirds do not fast to death, which has led to the suggestion that a refeeding signal might trigger egg desertion and departure to sea to refeed (17, 22) . Recently, the concept of a refeeding signal has found support in behavioral and metabolic data that show a spontaneous increase in locomotor activity of captive fasting but nonincubating emperor penguins (Aptenodytes forsteri) below a body mass threshold corresponding to an increase in body protein catabolism (28). This was interpreted as reflecting an increase in the drive to refeed and has led to the hypothesis that a shift from the preferential use of body lipid to that of body protein would be the metabolic signal that triggers refeeding. However, whether this applies to incubating birds, where the drive to incubate may overcome that for refeeding, is unknown. It is conceivable that the behav-Address for reprint requests and other correspondence: R. Groscolas, Centre d