Warming up for dinner: torpor and arousal in hibernating Natterer’s bats (Myotis nattereri) studied by radio telemetry

Abstract

The frequency and function of arousals during hibernation in free-living mammals are little known. We used temperature-sensitive radio transmitters to measure patterns of torpor, arousal and activity in wild Natterer's bats Myotis nattereri during hibernation. Duration of torpor bouts ranged from 0.06 to 20.4 days with individual means ranging from 0.9 to 8.9 days. Arousals from torpor occurred most commonly coincident with the time (relative to sunset) typical for bats emerging from summer roosts to forage. Bats with lower body condition indices had a shorter average duration of their torpor bouts. We found a non-linear relationship between duration of torpor bout and ambient temperature: the longest average torpor bouts were at temperatures between 2 and 4°C with shorter bouts at lower and higher ambient temperatures. One individual was radio-tracked for ten nights, remained active for an average of 297 min each night and was active for longer on warmer nights. Our results suggest that vespertilionid bats use relatively short torpor bouts during hibernation in a location with a maritime climate. We hypothesise that Natterer's bats time arousals to maximise opportunities for potential foraging during winter although winter feeding is not the sole determinant of arousal as bats still arouse at times when foraging is unlikely.

Spatiotemporal and demographic variation in the diet of New Zealand lesser short‐tailed bats (Mystacina tuberculata)

“…The difference in winter climate between the two sites could partially explain differences. Aerial insect abundance can decrease dramatically with decreasing T a (Jones et al., 1995), and T a  < 10°C has often been reported to constrain insect abundance (Hope & Jones, 2012; Park, Jones, & Ransome, 2000). During winter, mean night T a in Hauturu (12.1 ± 2.4°C) is higher than Pureora (6.2 ± 2.7°C), mean night T a  > 10°C occurred on 92% of observation nights in Hauturu compared to 7% in Pureora, and T a never dropped below 0°C in Hauturu but did so on 26% of nights in Pureora (Czenze, Brigham, Hickey, & Parsons, 2017a).…”

Hibernation energetics of free-ranging little brown bats

“…Most studies of torpor and hibernation in free-ranging mammals report on parameters associated with T b or skin temperature (T sk ) such as torpor bout duration or minimum torpid T sk (Hope and Jones, 2012;Michener, 1992;Munro et al, 2005;Park et al, 2000) but the commodity of interest for these studies is energy (Brigham et al, 2011;Willis, 2007). Estimates of hibernation energy requirements are important for answering fundamental and applied questions about hibernation, such as identifying crucial winter habitats for bats, and predicting impacts of disturbance, disease, yearto-year variation in weather patterns or climate change Boyles and Willis, 2010;Frick et al, 2010;Humphries et al, 2002;Landry-Cuerrier et al, 2008).…”

“…LandryCuerrier et al, 2008;Michener, 1992;Munro et al, 2005), only a handful of studies of thermoregulation during hibernation exist for free-ranging bats and many of these are for tropical or sub-tropical species (Cory Toussaint et al, 2010;Liu and Karasov, 2010;Stawski et al, 2009;Turbill, 2006;Turbill and Geiser, 2008). Very few studies have reported long-term body temperature profiles of temperate-zone bats in winter (Hope and Jones, 2012;Park et al, 2000). Temperate-zone bats may spend energy reserves differently from rodents during hibernation.…”

Echoes in the dark: Technological encounters with bats

“…This paper therefore proceeds through accounts of encounters with swarming bats and results from bat detection surveys between summer 2010 and winter 2011. Reflections on the embodied practice of detection are entwined with successful experiments in technological attunement, achieved through ongoing ecological monitoring of swarming and a study of hibernal ecology at Greywell Tunnel (see Hope and Jones, 2012). The threatened status of many European bat populations is concerning and demands action.…”

“…The study of hibernators in these climates is of particular relevance in light of climatic induced environmental change, whilst the devastating effect of the fungal pathogen Geomyces destructans on hibernating bats in North America (Frick et al, 2010) has highlighted the need for a better understanding of torpor patterns in wild bat populations. Research conducted by Hope and Jones (2012) sought to better understand the frequency of arousal from torpor in Natterer's bats, and investigate if one reason for arousal on winter nights is to take advantage of foraging opportunities.…”