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Hibernation by tree-roosting bats

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Abstract

In summer, long-eared bats (Nyctophilus spp.) roost under bark and in tree cavities, where they appear to benefit from diurnal heating of roosts. In contrast, hibernation is thought to require a cool stable temperature, suggesting they should prefer thermally insulated tree cavities during winter. To test this prediction, we quantified the winter thermoregulatory physiology and ecology of hibernating tree-roosting bats, Nyctophilus geoffroyi and N. gouldi in the field. Surprisingly, bats in winter continued to roost under exfoliating bark (65%) on the northern, sunny side of trees and in shallow tree cavities (35%). Despite passive re-warming of torpid bats by 10–20°C per day, torpor bouts lasted up to 15 days, although shorter bouts were also common. Arousals occurred more frequently and subsequent activity lasted longer on warmer nights, suggesting occasional winter foraging. We show that, because periodic arousals coincide with maximum roost temperatures, when costs of rewarming and normothermic thermoregulation are minimal, exposure to a daily temperature cycle could largely reduce energy expenditure during hibernation. Our study provides further evidence that models of torpor patterns and energy expenditure from hibernators in cold temperate climates are not directly applicable in milder climates, where prolonged torpor can be interspersed with more frequent arousals and occasional foraging.

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Abbreviations

MR:

Metabolic rate

T a :

Ambient temperature

T b :

Body temperature

T skin :

Skin temperature

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Acknowledgments

We thank Rebecca Drury for help trapping bats and Stuart Cairns for statistical guidance. This study was conducted under a Scientific Licence from the Department of Environment and Climate Change NSW and with the approval of the University of New England Animal Ethics Committee. The project was supported by a Student Scholarship from Bat Conservation International and an Australian Postgraduate Award to CT and a grant from the Australian Research Council to FG.

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Correspondence to Christopher Turbill.

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Communicated by I.D. Hume.

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Turbill, C., Geiser, F. Hibernation by tree-roosting bats. J Comp Physiol B 178, 597–605 (2008). https://doi.org/10.1007/s00360-007-0249-1

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