Daily rhythm of sleep-wakefulness in the starling, Sturnus vulgaris.

Wakefulness (W), slow wave sleep (SWS) and paradoxical sleep (PS) were recorded electrographically in four captive starlings Sturnus vulgaris under natural lighting conditions. Starling males slept considerably less than females in the period following sleep onset. The hourly percentage and episode durations of SWS slightly increased in the course of the night. The percentage of PS was highest during the first half of the night, then exhibited a decreasing trend. The episode durations of PS showed a flat maximum near midnight. The durations of total sleep (TS) episodes plus subsequently following W episodes showed an increase in the course of the night, with well marked periodic oscillations. The shortest episodes of TS and SWS exhibited clustering. The longest TS and SWS episodes occurred after midnight, unlike PS episodes. This study showed the importance of the natural day-night cycle in determining the daily pattern of wakefulness and sleep in the starling.