Social entrainment of the circadian rhythm in the flight activity of the microchiropteran bat Hipposideros speoris

Abstract

1. We investigated the problem of how members of the microchiropteran bat species Hipposideros speoris that live in a true cave clock their flight activity rhythms in the absence of time cues. 2. The bats become restless well in advance of sunset and then fly towards the cavemouth to sample light. 3. We investigated whether each bat roosting 40 m from the cave entrance must sample outside light levels for itself in order to emerge at the appropriate time. Three captive bats were tested and each began activity when the conspecifics left the cave in the evenings. 4. In another series of experiments a solitary bat was held captive in a solitary cave for 50 days and its circadian rhythm was recorded. In the absence of other conspecifics the circadian rhythm 'free ran' with a period shorter than 24 h. 5. We concluded from the results of our studies that there exists a clear-cut case for social synchronization of the circadian rhythms of this cave-dwelling bat.