Effects of reproductive condition, roost microclimate, and weather patterns on summer torpor use by a vespertilionid bat

• Published in: Ecology and evolution Vol. 4; no. 2; pp. 157 - 166
• Main Authors: Johnson, Joseph S., Lacki, Michael J.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.01.2014; John Wiley & Sons Ltd
• Subjects: Air temperature; Ambient temperature; Bats; Body temperature; Breastfeeding & lactation; Caves; Chiroptera; Corynorhinus rafinesquii; Cost control; Costs; day‐roosts; Ecological monitoring; ecophysiology; Energy; heterothermy; Hibernation; Hypotheses; Mammals; Mathematical models; Metabolism; Microclimate; microclimates; Original Research; Physiology; roosting ecology; Roosts; Skin; Skin temperature; Small mammals; Statistical analysis; Statistical models; Temperature; thermoregulation; Torpor; Variables; Weather; Weather patterns; United States > US; Kentucky; Corynorhinus rafinesquii; heterothermy; microclimates; day-roosts; ecophysiology; thermoregulation; Chiroptera; roosting ecology
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.913

A growing number of mammal species are recognized as heterothermic, capable of maintaining a high‐core body temperature or entering a state of metabolic suppression known as torpor. Small mammals can achieve large energetic savings when torpid, but they are also subject to ecological costs. Studying torpor use in an ecological and physiological context can help elucidate relative costs and benefits of torpor to different groups within a population. We measured skin temperatures of 46 adult Rafinesque's big‐eared bats (Corynorhinus rafinesquii) to evaluate thermoregulatory strategies of a heterothermic small mammal during the reproductive season. We compared daily average and minimum skin temperatures as well as the frequency, duration, and depth of torpor bouts of sex and reproductive classes of bats inhabiting day‐roosts with different thermal characteristics. We evaluated roosts with microclimates colder (caves) and warmer (buildings) than ambient air temperatures, as well as roosts with intermediate conditions (trees and rock crevices). Using Akaike's information criterion (AIC), we found that different statistical models best predicted various characteristics of torpor bouts. While the type of day‐roost best predicted the average number of torpor bouts that bats used each day, current weather variables best predicted daily average and minimum skin temperatures of bats, and reproductive condition best predicted average torpor bout depth and the average amount of time spent torpid each day by bats. Finding that different models best explain varying aspects of heterothermy illustrates the importance of torpor to both reproductive and nonreproductive small mammals and emphasizes the multifaceted nature of heterothermy and the need to collect data on numerous heterothermic response variables within an ecophysiological context. A growing number of mammal species are recognized as heterothermic, capable of achieving large energetic savings through the use of torpor. To better understand the conditions in which small mammals use torpor during the summer, we studied Rafinesque's big‐eared bats (Corynorhinus rafinesquii) using temperature‐sensitive radio telemetry. We found that different hypotheses explaining summer torpor each received strong support from our data in explaining different torpor variables, highlighting the multifaceted nature of torpor and the need to collect large datasets in an ecophysiological context.