Torpor and basking in a small arid zone marsupial
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The high energetic cost associated with endothermic rewarming from torpor is widely seen as a major disadvantage of torpor. We tested the hypothesis that small arid zone marsupials, which have limited access to energy in the form of food but ample access to solar radiation, employ basking to facilitate arousal from torpor and reduce the costs of rewarming. We investigated torpor patterns and basking behaviour in free-ranging fat-tailed dunnarts Sminthopsis crassicaudata (10 g) in autumn and winter using small, internal temperature-sensitive transmitters. Torpid animals emerged from their resting sites in cracking soil at ∼1000 h with body temperatures as low as 14.6°C and positioned themselves in the sun throughout the rewarming process. On average, torpor duration in autumn was shorter, and basking was less pronounced in autumn than in winter. These are the first observations of basking during rewarming in S. crassicaudata and only the second direct evidence of basking in a torpid mammal for the reduction of energetic costs during arousal from torpor and normothermia. Our findings suggest that although overlooked in the past, basking may be widely distributed amongst heterothermic mammals. Therefore, the energetic benefits from torpor use in wild animals may currently be underestimated.
KeywordsArousal Rate Daily Energy Expenditure Torpor Bout Arousal Phase Field Metabolic Rate
We would like to thank Rick Taylor, Mark Fletcher and Jade Freeman for their help at Kinchega National Park and Sarah Spachmann, Yvonne Würz, Clare Stawski and Jana Fleischmann for assistance in the field. Permits for the study were provided by the Animal Ethics Committee of the University of New England and National Parks and Wildlife Service NSW. The project was funded by grants from the Faculty of Sciences of the University of New England and the Wildlife Preservation Society of Australia to LW and from the Australian Research Council to FG. We thank National Parks and Wildlife Service NSW for providing accommodation during the field study.
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