The big brown bat, Eptesicus fuscus, is one of the most common bats hibernating in Indiana, hibernating in caves and buildings. It (along with many other species of bats) periodically arouses throughout the hibernation season. The significance of this winter activity of Eptesicus fuscus has been in contention in the literature for years. Brigham (1987) found that active bats collected in buildings around Ottawa, Canada were significantly lighter than animals remaining in hibernation. He proposed that these active, lighter bats were brought out of hibernation by critically low energy reserves. Other authors have advanced hypotheses that the bats arouse to eliminate metabolic waste, exercise, to move to a different roost, or drink (Sutter 1995). Many, such as Avery (1985), equate a special ultrasonic call known as a buzz with feeding. Since bats have been observed buzzing in the winter, it has been assumed by some authors that those bats are then necessarily feeding.
In the present study, I hope to elucidate the significance of winter activity by E. fuscus by: determining if a connection exists between the feeding buzz and foraging; determining if lighter bats are in poor physical condition or younger; to determine if bat activity levels in the winter are related to temperature (Sutter 1995) or barometric pressure; and to determine levels of roost fidelity in the hibernating population of E. fuscus at St. Mary-of-the-woods church. I will present methods to meet these objectives.
(1) Avery, M. I. 1985. Winter activity of pipistrelle bats. J. Animal Ecol., 54:721-738.
(2) Brigham, R. M. 1987. The significance of winter activity by the big brown bat (Eptesicus fuscus): The influence of energy reserves. Can. J. Zool, 65:1240-42.
(3) Mumford, R. E., and J. O. Whitaker, Jr. 1982. Mammals of Indiana. Indiana University Press: Bloomington. 537 pp.
(4) Sutter, C. L. 1995. Big brown bat, Eptesicus fuscus, hibernation energetics and microsite selection. Unpublished M. A. thesis, Indiana State University. 158 pp.