Biological alarm clock arouses hibernating big brown bats, Eptesicus fuscus

Abstract

This laboratory study showed that the individual averages of the times of day of arousal from hibernation of 55 big brown bats, Eptesicus fuscus, maintained in darkness, ranged from 14:05 to 20:50 (2:05 p.m. to 8:50 p.m.). The data were interpreted as representing a persistent but inexact 24-h rhythm that functioned as a biological alarm clock. This rhythm was, according to the parameters measured, apparent only on the day of arousal. The rhythm was determined to be independent of the length of time the bat had hibernated; independent of temperature; persistent and did not drift and become free-running in continuous darkness; unapparent in daily cardiac patterns or themogenic activity; and independent of obvious exogenous variables.