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.