Winter activity of boreal bats

Anna S Blomberg,Melissa B Meierhofer,Tapio Eeva,Ville Vasko,Joseph S Johnson,Thomas M Lilley

doi:10.1007/s42991-021-00111-8

Abstract

Natural hibernation sites used by bats in areas that lack cave features have long remained unresolved. To investigate hibernation site selection and winter activity of boreal bats, we recorded bat calls using passive acoustic monitoring at 16 sites in South-Western Finland. These sites included four rock outcrops with crevices and cave features, three glacial erratics or boulder fields, three ancient shores, three root cellars and three control sites where we did not expect bats to be overwintering. Our results revealed echolocation calls of Eptesicus nilssonii, Plecotus auritus and Myotis sp. We recorded significantly more activity near rock outcrops compared to other habitats, excluding root cellars. We also found that ambient temperature had a positive effect on bat activity and found evidence that P. auritus may be using low barometric pressure as a proxy for suitable foraging conditions during the winter. Our results suggest that rock outcrops may be more important to bats than previously acknowledged, highlighting the need to take these sites in account in planning of conservation measures. Furthermore, our findings underline the suitability of using acoustic monitoring in homing on hibernation sites that are not otherwise accessible.

Highlights

Insectivorous bats living at high latitudes face enormous fluctuations in the seasonal availability of food
Monitoring site classes selected for the studies included ancient shores (N = 3), rock outcrops with caves and/or crack features (N = 4, Fig. 1), glacial erratic formations or boulder fields (N = 3), and root cellars (N = 3), of which the latter were known to be used by bats during the winter as hibernation sites
Our results revealed significantly more calls of E. nilssonii (N = 182) than P. auritus (N = 66; t = 5.17; df = 405; P < 0.001) and Myotis species (N = 34; t = 5.56; df = 405; P < 0.001; Table 2)

Summary

Introduction

Insectivorous bats living at high latitudes face enormous fluctuations in the seasonal availability of food. Bats can respond to this challenge either by migrating to warmer areas, where food is occasionally available throughout the winter and hibernation is less risky (Popa-Lisseanu and Voigt 2009), or they can hibernate in situ, by utilizing fat reserves accumulated before the winter (Geiser 2013). Management, Texas A&M University, College Station, TX, USA 4 Department of Biological Sciences, Ohio University, Athens, OH, USA of extended bouts of torpor, during which bats lower their body temperature close to ambient temperature of the hibernaculum and decrease their metabolic rate (Geiser 2004; Guppy and Withers 2007). Due to the long winters at high latitudes, bats must shift their microclimate preference towards colder ambient temperatures and longer torpor bouts to conserve energy (Dunbar and Brigham 2010). Results of winter activity studies conducted in milder climates, where food is available throughout the winter, are not applicable in the north (Hope and Jones 2012)

Methods

Results

Conclusion