EEG and behavioral criteria to define vigilance states in the white-crowned sparrow. A. Representative examples of EEG recordings of each vigilance state. Arrow indicates onset of REM sleep. B. Hypnograms showing the 24-hour time course of waking (W), drowsiness (D), SWS sleep (S) and REM sleep (R) for each of the 6 birds during baseline. Behavioral states were scored in 4-sec epochs. However, because state transitions are frequent in sparrows, for each behavioral state only those episodes lasting > 16 seconds, and occurring without any interruption lasting > 16 seconds, are plotted. Bottom: two 1-hour periods with every 4-sec epoch plotted are shown to better illustrate the characteristic rapid transition between sleep to waking in sparrows.