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First published online November 30, 2007
Journal of Experimental Biology 210, 4345-4350 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.007294

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Energy availability influences microclimate selection of hibernating bats

Justin G. Boyles^1,*, Miranda B. Dunbar², Jonathan J. Storm³ and Virgil Brack, Jr¹

¹ Center for North American Bat Research and Conservation, Department of Ecology and Organismal Biology, Indiana State University, Terre Haute, IN 47809, USA
² Department of Biology, University of Regina, Saskatchewan, S4S 0A2, Canada
³ Department of Ecology and Organismal Biology, Indiana State University, Terre Haute, IN 47809, USA

^* Author for correspondence (e-mail: jboyles3{at}mymail.indstate.edu)

Accepted 30 September 2007

Many species hibernate to conserve energy during periods of low food and water availability. It has long been assumed that the optimal hibernation strategy involves long, deep bouts of torpor that minimize energy expenditure. However, hibernation has ecological (e.g. decreased predator avoidance) and physiological (e.g. sleep deprivation) costs that must be balanced with energy savings; therefore, individuals possessing sufficient energy reserves may reduce their use of deep torpor. We tested the hypothesis that energy (fat) availability influences temperature selection of two fat-storing bat species during hibernation. We predicted that individuals with small energy reserves would select colder temperatures for hibernation in order to minimize energy expenditure, while individuals with larger energy reserves would choose warmer temperatures to minimize the costs of hibernation. Results from our field experiment indicate that little brown myotis (Myotis lucifugus) hibernating in warm microclimates were significantly heavier than individuals hibernating in cooler microclimates. To determine if energy availability was mediating this relationship, we limited fatty acid availability with mercaptoacetate (MA) and quantified its effect on torpid metabolic rate (TMR) and thermal preference of big brown bats (Eptesicus fuscus). Administration of MA caused a 43% drop in TMR at 10°C and caused bats to choose significantly colder temperatures for hibernation. Our results suggest that fat-storing bats minimize torpor expression using both physiological and behavioral mechanisms.

Key words: Eptesicus fuscus, fat storing, hibernation, metabolic depression, Myotis lucifugus, respirometry, thermal preference

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