To use or not to use torpor? Activity and body temperature as predictors
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When food is limited and/or environmental conditions are unfavourable, many mammals reduce activity and use torpor to save energy. Nevertheless, reliable predictors for torpor occurrence, especially in the wild, are currently not available. Interrelations between torpor use and other energy conserving strategies are also poorly understood. We tested the hypothesis that reductions in normothermic body temperature (T b) and the period of activity before torpor events could be used as predictors for torpor occurrence in sugar gliders, Petaurus breviceps (body mass, ∼125 g), known to display daily torpor in the wild. Occurrence of torpor was preceded by significant (∼10–25%) reductions of the duration of the activity phase. Moreover, the normothermic resting T b fell by an average of 1.2°C over 3 days before a torpor event, relative to individuals that did not display torpor. Our new findings suggest that before entering torpor, sugar gliders, which appear to use torpor as an emergency measure rather than a routine energy saving strategy, systematically reduce activity times and normothermic resting T bs to lower energy expenditure and perhaps to avoid employing torpor. Thus, reduced activity and normothermic T b may provide a predictive tool for the occurrence of daily torpor in the wild.
KeywordsTorpor Activity Body temperature Sugar glider Weather Marsupial
We would like to thank Stuart Cairns for his help with the statistical analysis and comments on the text. We would also like to thank Frank Falkenstein, Nicola Goodship, Marco Wenzel and Wendy Westman for their help in the field. Permits for all animal experiments were provided by the New South Wales National Parks and Wildlife Service and the University of New England Animal Ethics Committee. This work was supported by an ARC grant awarded to FG.
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