Sleep changes in emperor penguins during fasting.

The proportion and the distribution over 24 h of the different arousal stages characterized in emperor penguins [wakefulness (W), drowsiness (D), slow-wave sleep (SWS), and paradoxical sleep (PS)] were studied under natural ambient conditions in four subjects that were first fed and then deprived of food for 7-18 days. In both fed and fasting states, each arousal stage was distributed through numerous episodes of short duration. The fasting state provoked only a slight increase in D. There was, however, a large increase in SWS, which increased from 37.5 to 55.4%/day, mainly at the expense of W, which fell from 42.7 to 21.9%/day, in close relation to the first two fasting phases when proteins were saved and when most of the energy was derived from lipids. PS proportions were lower during fasting (from 5.7 to 2.4%/day). These changes in the arousal stages in emperor penguins are examined for their implications in sleep mechanisms and energy saving. Their possible consequences, due to the reduced alertness, are also discussed.