ADAPTIVE ASPECTS OF ACTIVITY RHYTHMS IN BATS

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Abstract
The interaction of exogenous light clues and an endogenous timing element in the regulation of the locomotor activity rhythm was demonstrated for nocturnal bats, and the means by which these bats evaluate the daily light cycle changes were considered. Under constant dark conditions in the laboratory, non-24-hour (circadian) rhythms were seen, but on a 24-hour light-dark cycle the bats gradually adjusted the time of activity to correspond to the period of darkness. Bats roosting in a darkened artificial cave in the laboratory, or under natural conditions in a darkened church loft, without a direct view of the daily light-dark cycle, anticipated the dark period by flying up to the end of the artificial cave or to the exit window of the church loft. Apparently such behavior prior to the light-dark transition was the chief means of synchronizing a free-running activity rhythm to the daily light cycle. The significance of the data to current theories of rhythmic daily entrainment phenomena is also discussed.