A study of sleep in the European blackbird.

Sleep states in the blackbird, Turdus merula, were determined by recording the electroencephalogram (EEG), electrooculogram (EOG), electromyogram (EMG), and heart rate (HR), and from behavioral observations and responses to auditory stimulation by natural calls. The presence of changes in slow wave activity was determined from the power spectra of the EEG. Spectral power density in the 0.5-4.0 Hz band during slow wave sleep (SWS) attained highest values in the first part of the night, then declined. This trend in EEG spectra, which occurred across the night, probably reflects a homeostatic process strikingly similar to that observed in mammals. The reactivity to natural calls during SWS episodes also decreased across the night. Episodes of interhemispheric EEG asymmetry, which typically lasted from 2 to 4 s, occurred when birds displayed the front sleep posture and they constituted 140-200 s of each night. Unihemispheric sleep episodes probably result from unilateral activation of the visual system, and they could be considered as an evolutionary adaptation. HR was highest in wakefulness and lower in sleep but, due to large variability, reliable discrimination between sleep and wakefulness could not be made. Comparison of the blackbird's behavior during 4 different nights revealed a strong effect of the first night on sleeping behavior. A significant reduction in back sleep posture occurred during the baseline night, when lead wires were connected.

Annual and weekly changes in the sleep-wake rhythm of school children.

Sleep-wake patterns in 10- and 14-year-old children were followed over a year using sleep diaries kept during 2-week periods every 5 weeks. The times of awakening and sleep duration closely followed the annual and weekly alternations of schooldays and holidays. During vacations, sleep duration increased considerably as compared to the school year. The clear decrease in sleep duration was observed in spring only for 14-year-olds. Weekly changes of sleep patterns during the school year disappeared during vacations. It was concluded that sleep duration in children is closely related to the school schedules and could be a result of sleep deprivation and recovery.

Electrophysiological and behavioral correlates of sleep in the blackbird (Turdus merula).

Sleep in five blackbirds was investigated by continuous 24-h recordings of EEG, EOG, EMG, HR, and behavior. Because these recordings were similar in many respects to those obtained previously in other species, it was possible to define the electrophysiological correlates of active wakefulness (AW), quiet wakefulness (QW), slow wave sleep (SWS), and paradoxical sleep (PS). The time spent in SWS and PS was 32.2% and 5.7% of the 24-h period, respectively. The amount of SWS decreased during the course of the dark period, whereas PS exhibited an increasing trend. In addition, SWS always preceded PS, as in mammals. Thus, homeotherms may share common mechanisms of sleep regulation. Blackbirds turned their heads so that their beaks pointed backwards only during darkness. This back posture was usually associated with sleep. Head nodding, which occurred only when the beak pointed forward, was observed during 13% of PS episodes. Eye closure was a reliable behavioral index of sleep. Detailed behavioral observations alone do not provide sufficient information for the accurate assessment of sleep stages in blackbirds.

Influence of environmental temperature and photoperiod on temporal structure of sleep in corvids.

A survey is presented of the author's own investigations on the effects of ambient temperature and photoperiod on sleep in corvids. Daily sleep patterns of rook, Corvus frugilegus and magpie, Pica pica have been studied electrographically under natural ambient conditions of light and temperature. The daily amount of total sleep time (TST) was positively correlated with night duration, whereas the proportion of TST spent in paradoxical sleep (PS) was strongly reduced in low ambient temperature (Ta). The mean duration of sleep cycle was found to be positively correlated with Ta. The temporal structure of PS in contrast to that of slow wave sleep (SWS) underwent dramatic changes due to cold exposure. In cold PS episodes appeared randomly throughout the night. The systematic trend observed in nocturnal distributions of SWS did not vary significantly when Ta changed from thermoneutral to moderate cold. This study provided indirect support for the view that PS in birds, like in mammals, is associated with inhibition of thermoregulatory responses.

Daily distribution of sleep states in the rook Corvus frugilegus.

Sleep and wake states were monitored polygraphically in the rook Corvus frugilegus, under the natural photoperiod and temperature. The indices of sleep and wake states in the rook were similar to those described previously for birds in general. The appearance of sleep episodes was confined to the dark part of the photoperiod. Slow wave sleep (SWS) showed a tendency to increase during the course of the night, while paradoxical sleep (PS) showed the opposite trend. The distribution of short SWS episodes were clustered into two groups, one group occurred in the period following the onset of sleep and the other, less prominent group occurred towards the end of sleep. The longest episodes of SWS appeared in the second half of the night, whereas those of PS appeared after onset of sleep.

Distribution of sleep and wakefulness in 24-h light-dark cycles in the juvenile and adult magpie, Pica pica.

The daily organization of sleep and wakefulness was examined electrographically under natural conditions in captive juvenile and adult magpies, Pica pica. Electrographic indices of sleep in the magpie were found to be similar to those of other avian species. The daily amount of TS in juveniles was 17% greater than in adults. The amount of paradoxical sleep (PS) in adults was one-fifth that of juveniles. In adults sleep was confined to darkness, while in juveniles it also occurred during the light period. SWS in adults was almost constant, while PS slightly increased across the night. No systematic trends were observed in juveniles. In both groups of birds, the longest sleep episodes appeared around midnight.

Daily distribution of sleep states in the jackdaw, Corvus monedula.

Polygraphic and behavioral studies of the jackdaws Corvus monedula have revealed a strong influence of the natural day-night cycle on their daily wakefulness-sleep activity. The jackdaws were behaviorally active during the light part of the photoperiod. The daily distribution of slow wave sleep (SWS) was symmetric and that of paradoxical sleep (PS) was asymmetric. The amount of PS was greater in the second half of the night than in the first. Short and intermediate length episodes occurred almost homogeneously throughout the night. The longest sleep episodes clustered toward the middle part of the night and did not occur in the periods following onset of sleep and before the end of sleep.

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.

Sleep pattern in the rook, Corvus frugilegus.

In the rook, Corvus frugilegus, electrographic and behavioural correlates of sleep and wakefulness have been determined under natural lighting conditions. Slow wave sleep (SWS) was characterized by high amplitude slow EEG activity, low neck EMG, and behavioural inactivity. Paradoxical sleep (PS) was characterized by low amplitude fast EEG activity and inconsistent decrease in EMG. PS episodes always commenced with head downward. Several eye movements occurred activity were present. The rook spent in sleep 31.8% of the 24-h period. PS however, eye movements, high tonic neck EMG activity, and behavioural activity were present. The rook spent in sleep 31.8% of the 24-h period. PS constituted 1.8% of total sleep, while the rest of total sleep was occupied by SWS. On the average, episodes of SWS and PS lasted 10.8 min and 24 s respectively. The daily percentage of SWS was highly correlated with the mean episode duration. PS amount was better correlated with the number of episodes than with their mean duration. Our data suggest that over-short period of recovery from surgery and adaptation with implanted electrodes could lead to underestimation of sleep duration in rook.

Sleep pattern in the starling (Sturnus vulgaris).

Electrographic and behavioural observations were conducted on two male and two female captive starlings (Sturnus vulgaris) under natural illumination conditions during autumn. Polygraphically sleep and wakefulness of starling were similar to those of other birds. Starling's total sleep (TS) and slow wave sleep (SWS) lasted 39.0 +/- 1.4% and 38.3 +/- 1.7% of the 24-h period respectively. Paradoxical sleep (PS) was 1.8 +/- 0.2% of the total sleep time. The mean durations individual of TS, SWS and PS episodes were 6.8 +/- 0.2 min, 5.0 +/- 1.0 min and 18 +/- 3 s respectively. The daily percentage of SWS was correlated with the mean episode duration while that of PS was correlated with the number of episodes rather than with the mean episode duration. Starling females spent in sleep a greater percentage of the 24-h period than males.