The duration of the period of hibernation of three species of vespertilionid bats. I: Field studies

The durations of the periods of hibernation of the big brown bat (Eptesicus fuscus), little brown bat (Myotis lucifugus), and eastern pipistrelle (Pipistrellus subflavus) under natural conditions were determined by following intracave movements through two winter seasons in two Missouri caves. Average durations of periods of hibernation were similar for all three species (10–20 days) over a range of temperatures. Maximum durations of periods of hibernation determined were as follows: E. fuscus, 72 days; P. subflavus, 111 days (?); M. lucifugus, 83 days. Variability in the durations of the period of hibernation was much greater for P. subflavus and may be attributable to a lack of movement after arousal or the inability of the observer to discern movement between periods of hibernation. The frequency of arousal was determined to be statistically temperature dependent for M. lucifugus, but not for E. fuscus or P. subflavus, probably because of insufficient data.