Journal of Experimental Biology 2012 215: iii doi: 10.1242/jeb.074823
Fitting temperature-sensitive radio transmitters to 22 bats hibernating in a small cave in central Manitoba, Canada, the duo monitored the bats' body temperatures for 3 months. Recording the lengthy periods when the bats became torpid (13.1 days on average), depressing their body temperatures, and the brief arousals when the animals returned their body temperatures to normal, Willis and Jonasson found that the duration of torpor varied significantly from animal to animal. They also found that the bats were torpid for an impressive 99.6% of the hibernation period.
Next, the pair analysed the temperature recordings to find out whether the bats' age, sex or body condition affected their hibernation. They did not. However, when the scientists analysed the arousal periods, they noticed something unusual. Occasionally the bats dropped their body temperatures slightly during arousal and entered a period of shallow torpor. The duo suspects that the bats use these bouts – which they refer to as heterothermic arousal – to minimise the over all metabolic costs of hibernation. Finally, the team measured the masses of the tiny animals to estimate their energy use over the course of the hibernation, and found that their calculated predictions of energy use agreed well with the bats' mass loss, although the calculations slightly overestimated the energy consumption.
Having assessed the mammal's hibernation energetics, Willis says, ‘Our findings will be important for understanding the energetic and survival implications for bats suffering from white-nose syndrome.’
Jonasson, K. A. and
Willis, C. K. R. (2012). Hibernation energetics of free-ranging little brown bats. J. Exp. Biol. 215,2141-2149.
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