Katie Day

Date of Graduation

Fall 2008


Master of Science in Biology



Committee Chair

Thomas Tomasi


Indiana bat, Myotis sodalis, metabolism, temperature, hibernation, torpor

Subject Categories



Endangered Indiana bats (Myotis sodalis) have decreased by 48% nationwide in the last 40 years. One theory to explain this decline is increasing cave temperatures in winter hibernacula. Altering cave temperatures can affect torpid bats by raising metabolism and causing more arousals, both of which use more fat reserves. In addition, fluctuations in cave temperatures may cause additional arousals. Unfortunately, no studies have addressed this issue. Female Indiana bats (n = 36) were collected from caves just prior to hibernation. These bats were maintained in an environmental chamber that simulated hibernacula conditions. Some bats (n = 24) had an iBBat temperature-sensitive datalogger temporarily attached to their backs that recorded a skin temperature every 30 minutes throughout the winter. One environmental chamber was set at 8°, 6°, and 4°C over the winter. The second chamber experienced the same mean temperatures over the same timetable, but temperature fluctuated+- 2°C on a regular basis. Torpor bouts were longest at 4°C, and were not affected by temperature fluctuations. However, the temperature fluctuations appeared to cause longer arousals. The rest of the bats (n = 12) were individually placed in metabolic chambers at 9°, 7°, 5°, 3°, and 1°C to calculate oxygen consumption during torpor, and during arousals at 9°, 7°, 5°, and 3°C. Torpid metabolism was affected by temperature; particularly, torpor metabolism at 9°C was higher than at 7° or 5°C. Although metabolism for arousals was not different among temperature treatments, oxygen consumption rates are almost 200 times higher than torpid oxygen consumption rates at the same temperatures. These numbers were used to calculate a winter energy budget, and determine an optimum hibernation temperature (3-6°C) for female Indiana bats. Hibernacula that provide these conditions deserve extra protection.


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