Characteristic of sleep and wakefulness in a walrus

Parameter	Sleep on land, N = 5	Sleep in water, N = 3
Total sleep time, % of 24-h	26.3 ± 1.9 (21.9, 31.3)	21.6 ± 1.4 (19.2, 23.9)
Slow wave sleep (SWS), % of 24-h	19.4 ± 2.0 (15.5, 24.4)	20.5 ± 0.8 (19.0, 21.8)
Paradoxical sleep (PS), % of 24-h	6.9 ± 1.1 (5.5, 7.8)	1.1 ± 0.6 (0.1, 2.1)
Duration of bilateral SWS, % total SWS	90.2 ± 2.1 (85.6, 96.1)	96.7 ± 0.9 (95.8, 98.5)
Number of PS episodes during the 24-h period	15 ± 2 (11, 21)	13 ± 4* (9, 16)
Duration of PS episodes, min**	6.4 ± 0.6 (0.3, 22.7)	1.8 ± 0.1 (0.7, 3.3)

Note: The data presented as mean ± SEM. Minimal and maximal values are given in parentheses. N—number of recording sessions (days).

^*The mean values were calculated for the 2nd and 3rd recording days. Only one episode lasting 2.0 min was recorded on the first day.

^**The durations of PS episodes on land and in water were calculated for all recorded episodes—76 episodes when on land and 26 episodes when in water.