Refeeding signal in fasting-incubating king penguins: changes in behavior and egg temperature

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 biotelemetry, 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 +/- 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 degrees 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.