Sleep patterns in the owl Strix aluco

In two owls the occurrence of paradoxical sleep was tested both behaviorally and electrographically. The waking and sleeping states of the owl can be clearly distinguished. Sleep consisted of two phases: a phase covering most of the sleep which is characterized by motionless posture, slow high-voltage EEG waves, reduced EMG activity of the neck muscles compared with the waking EMG, tonic bradycardia, reduced respiration rate and absence of eye movements; a phase occurring periodically, which is characterized by motionless posture, complete eyelid closure, absence of eye movements, presence of tonic EMG activity and by low voltage fast EEG pattern. Occasionally, this phase of sleep was associated with cardiac irregularities, respiratory apnea and gross body twitches. Thus this phase of sleep was considered to be analogous to the paradoxical sleep of mammals.