An electrophysiological and behavioral study of sleep in emperor penguins under natural ambient conditions

In two pairs of emperor penguins surgically implanted for chronic recordings of EEG, EOG and EMG, four arousal stages were characterized on the basis of behavioral and electrophysiological criteria: wakefulness (W), drowsiness (D), slow-wave sleep (SWS) and paradoxical sleep (PS). The general patterns of electrographic correlates observed for each arousal stage resemble those reported in other birds. Sleep patterns were examined with these two pairs placed under natural ambient conditions of light and air temperature, the first pair being exposed to moderate cold under alternate conditions of day and night, and the second studied when daylight was total at thermoneutrality. The time spent in sleep (TST) by each group was 41.3% and 45.1% of the 24 hr period respectively, the difference not being significant. As in other birds, PS occurred in very brief episodes lasting, on average, 8 to 10 seconds and occupying only 5 to 6% of the 24 hr period. Whatever the external conditions, the PS to TST ratio appeared to remain unchanged (12 to 14%). Its relatively high value is discussed in relation to predation susceptibility.