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Various exogenous or endogenous factors may induce an emergency response in birds, redirecting current activity towards survival. In fasting, breeding penguins, the achievement of a critical energy depletion was suggested to induce egg abandonment and departure to sea for re-feeding. How such a behavioral shift is hormonally controlled remains unknown. The possible involvement of corticosterone and prolactin was examined by characterizing the nutritional and hormonal states of king penguins at egg abandonment. Further, we tested if these states differ according to whether an egg or a chick is abandoned, and according to the timing of breeding. In every case of abandonment, birds were in phase III fasting characterized by accelerated protein catabolism. However, body condition at egg abandonment was lower in early than in late breeders, suggesting that king penguins are willing to tolerate a larger …