Hibernation of the Big Brown Bat, Eptesicus fuscus, in Buildings

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Although little empirical evidence was available prior to our study, many big brown bats, Eptesicus fuscus, were thought to hibernate in buildings in or near their summer roost. A total of 189 maternity colonies of Eptesicus was located during the summers of 1987 and 1988 in buildings in Indiana and extreme eastcentral Illinois. Numbers of individuals occupying the summer colonies were counted. Sixty-seven roost sites with characteristics that might make them suitable as hibernacula were revisited in winter and examined for hibernating bats. In 32 sites, one to 86 hibernating big brown bats were found (total, 593; X̄ = 9.3). Most bats were solitary, but some formed small groups. Temperatures in hibernacula ranged from 3–20°C at times that hibernating bats were observed. Thirteen other buildings lacking maternity colonies contained hibernating bats, one for 3 consecutive years, and three for 2 consecutive years.