Long‐term video surveillance and automated analyses reveal arousal patterns in groups of hibernating bats

Abstract

Understanding natural behaviours is essential to determining how animals deal with new threats (e.g. emerging diseases). However, natural behaviours of animals with cryptic lifestyles, like hibernating bats, are often poorly characterized. White‐nose syndrome (WNS) is an unprecedented disease threatening multiple species of hibernating bats, and pathogen‐induced changes to host behaviour may contribute to mortality. To better understand the behaviours of hibernating bats and how they might relate to WNS, we developed new ways of studying hibernation across entire seasons. We used thermal‐imaging video surveillance cameras to observe little brown bats (Myotis lucifugus) and Indiana bats (M. sodalis) in two caves over multiple winters. We developed new, sharable software to test for autocorrelation and periodicity of arousal signals in recorded video. We processed 740 days (17,760 hr) of video at a rate of >1,000 hr of video imagery in less than 1 hr using a desktop computer with sufficient resolution to detect increases in arousals during midwinter in both species and clear signals of daily arousal periodicity in infected M. sodalis. Our unexpected finding of periodic synchronous group arousals in hibernating bats demonstrate the potential for video methods and suggest some bats may have innate behavioural strategies for coping with WNS. Surveillance video and accessible analysis software make it now practical to investigate long‐term behaviours of hibernating bats and other hard‐to‐study animals.

Long-term patterns of cave-exiting activity of hibernating bats in western North America

“…Although we counted almost 15 times more of that species than western small-footed myotis during hibernacula surveys, because small-footed myotis are more difficult to observe when hibernating 73 , 74 , we documented western small-footed myotis exiting caves after arousal from torpor during hibernation on average 3 times more than Townsend’s big-eared bats. Different arousal and flying patterns during winter have been documented for other species hibernating together 3 , 75 , 76 , and generally it takes more energy for larger bats to arouse and fly than smaller bats 20 , 77 . Also, difficulty exists when comparing winter activity of bat species using acoustic recordings, because of species-specific differences in intensity of echolocation calls and atmospheric attenuation 57 , 61 , 78 , especially for Townsend’s big-eared bats as their calls are lower intensity compared with calls of western small-footed myotis 52 , 60 .…”

Possibility for reverse zoonotic transmission of SARS-CoV-2 to free-ranging wildlife: A case study of bats

“…At least 25 of the ecologically diverse vespertilionid species of bats in the US and Canada hibernate [ 86 ], which might influence their susceptibility to or interactions with viruses, as has been postulated for common vespertilionids infected with α-CoVs and rabies virus [ 44 , 87 – 89 ]. Hibernation strategies vary among species of bats (e.g., degree of sociality, thermoregulatory behaviors, habitat selection) [ 90 ], but bat body temperatures during hibernation generally remain consistently below 10º C for periods lasting 7–9 months per year [ 91 ], providing a potential mechanism to limit viral replication and spread [ 92 ]. Experimental studies to assess the ability of SARS-CoV-2 or other β-CoVs to survive and replicate in bats (cell lines and individuals) at low temperatures [ 92 , 93 ] would provide additional insight into risk of reverse zoonosis.…”

“…Examples of other “hands-off” methods applicable to both bat disease and conservation research include the following: virus discovery and characterization focused on existing specimens archived in scientific museums or through partnerships and collaboration with established national bat disease monitoring or surveillance programs [ 147 , 148 ]; monitoring echolocation calls to determine the occurrence, distributions, and seasonal or nightly activity patterns of bats [ 133 , 149 ]; digital imaging methods for counting bats and studying physiology and behaviors in the context of disease [ 90 , 108 ]; sampling guano from below bat roosts to determine bat species and individual identity, population dynamics, and daily or seasonal patterns of bat occupancy and pathogen shedding [ 71 , 150 – 152 ]; and mathematical modeling to predict susceptible host species, virus sharing among hosts, spread patterns, or to estimate mortality in affected populations [ 5 , 70 , 122 , 135 ]. Promising areas for innovation include making technologies for bat research more accessible to a broader global user base, less expensive, easier to use, and scientifically reproducible through open-source hardware, software, and laboratory methods [ 153 , 154 ].…”

Hibernation temperature-dependentPseudogymnoascus destructansinfection intensity in Palearctic bats

“…The stability of the body surface temperature facilitated us to model the infection intensity as expressed by the fungal load and the number of UV fluorescent skin lesions relative to body surface temperatures measured at the end of hibernation. Other species may choose different temperatures at different points in winter even within the same cave system (Figure 1), but without more data collected with temperature sensitive data-loggers on hibernating bats [ 38,68], we are currently at the limit of what is known. Moreover, the same species use different temperatures across their distribution range and different species choose different temperatures within one hibernaculum ( Figure 1).…”