Vigilance states and body temperature during the circadian cycle in fed and fasted pigeons (Columba livia).

Fasting induces nocturnal hypothermia in pigeons. Slow-wave sleep (SWS) and paradoxical sleep (PS) are associated with reduced heat production in pigeons. The possibility that fasting-induced nocturnal hypothermia is related to increased SWS and PS was examined by comparing body temperature (Tb) and vigilance states when pigeons were fed and fasted. The results showed that when Tb is decreasing near the beginning of the dark phase, the percentage of total recording time (%TRT) spent in SWS and PS was elevated in fasting due to increased frequency of episodes and increased duration of PS episodes. When Tb was low during the middle segment of the dark phase, SWS was elevated in fasting due to increased episode duration. However, fasting did not alter PS, which increased in %TRT across the segment due to increased episode frequency. When Tb was rising during the final hours of dark, SWS remained elevated in fasting and %TRT in SWS and PS was relatively high. SWS and PS may promote the fasting pigeon's entry into, and maintenance of, nocturnal hypothermia.