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Summer heterothermy in Rafinesque’s big-eared bats (Corynorhinus rafinesquii) roosting in tree cavities in bottomland hardwood forests

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Abstract

Many small mammals are heterothermic endotherms capable of maintaining an elevated core body temperature or reducing their thermoregulatory set point to enter a state of torpor. Torpor can confer substantial energy savings, but also incurs ecological costs, such as hindering allocation of energy towards reproduction. We placed temperature-sensitive radio transmitters on 44 adult Rafinesque’s big-eared bats (Corynorhinus rafinesquii) and deployed microclimate dataloggers inside 34 day roosts to compare the use of torpor by different sex and reproductive classes of bats during the summer. We collected 324 bat-days of skin-temperature data from 36 females and 4 males. Reproductive females employed fewer torpor bouts per day than non-reproductive females and males (P < 0.0001), and pregnant and lactating females had higher average (P < 0.0001) and minimum (P < 0.0001) skin temperatures than non-reproductive females. Pregnant females spent less time torpid (P < 0.0001) than non-reproductive females, but lactating females used relatively deep, long torpor bouts. Microclimates varied inside tree species with different configurations of entrances to the roost cavity (P < 0.0001). Bats spent more time torpid when roosting in water tupelo (Nyssa aquatica) trees possessing only a basal entrance to the cavity (P = 0.001). Of the tree species used as roosts, water tupelo cavities exhibited the least variable daytime and nighttime temperatures. These data demonstrate that use of summer torpor is not uniform among sex and reproductive classes in Rafinesque’s big-eared bat, and variation in microclimate among tree roosts due to species and structural characteristics facilitates the use of different thermoregulatory strategies in these bats.

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Acknowledgments

Funding for this project was provided by the Kentucky Department of Fish and Wildlife Resources (KDFWR) and the University of Kentucky, College of Agriculture. We thank G. Langlois, D. Fraser, J. Grider, C. Farr, and H. Comstock for their hard work and dedication in the field, without which this project would not have been possible. We also thank J. MacGregor, B. Hines, and D. Baxley of the KDFWR for their guidance. All methods were approved by the University of Kentucky Institutional Animal Care and Use Committee (IACUC No. A3336-01). This investigation is connected with a project of the Kentucky Agricultural Experiment Station (KAES No. 12-09-093) and is published with the approval of the director.

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  1. Department of Forestry, University of Kentucky, Lexington, KY, 40546, USA

    Joseph S. Johnson & Michael J. Lacki

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  1. Joseph S. Johnson
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Correspondence to Joseph S. Johnson.

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Communicated by G. Heldmaier.

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Johnson, J.S., Lacki, M.J. Summer heterothermy in Rafinesque’s big-eared bats (Corynorhinus rafinesquii) roosting in tree cavities in bottomland hardwood forests. J Comp Physiol B 183, 709–721 (2013). https://doi.org/10.1007/s00360-012-0728-x

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  • DOI: https://doi.org/10.1007/s00360-012-0728-x

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