King penguin chicks (Aptenodytes patagonicus, Miller J. F. 1778) experience a severe nutritional shortage when left alone for a long period of time, and they may be fed infrequently or not at all by their parents during the austral winter (Cherel et al., 1987). Yet, the energetic demands remain elevated because of somatic growth, tissue maturation, thermogenesis and activity against predators. Although young king penguins can tolerate the loss of 70% of their body mass, a high percentage of the growing chicks fails to support the energy cost associated with thermoregulation and predation pressure and will die by the end of winter because of a shortage of fuel (Cherel et al., 1987). Nevertheless, king penguin chicks show an exceptional fasting endurance for up to 5 months (Cherel and Le Maho, 1985), indicating that they have evolved adaptive responses to the lack of food, which primarily favours the development of a whole range of energy conservation mechanisms. Firstly, chicks are anatomically (large size, round shape, high thermal insulation) and behaviourally (huddles) well adapted to minimize heat dissipation in harsh environmental conditions (Barré, 1984; Le Bohec et al., 2005). Secondly, the winter energy expenditure is physiologically reduced by lowering the plasma level of thyroid hormones and the amount of metabolically active tissues, thereby minimizing the basal metabolic rate and the metabolic cost of growth (Barré, 1984; Cherel and Le Maho, 1985; Cherel et al., 1987; Cherel et al., 1993a; Cherel et al., 2004; Duchamp et al., 1989). Thirdly, the development of seasonal heterothermy (Eichhorn et al., 2011), together with a low thermogenic effect of circulating lipids (Teulier et al., 2013), further indicate a reduced energy investment into heat production and thermoregulation. All these energy-saving mechanisms maximize the survival of chicks in winter during this long period of food shortage.