Feasting, not fasting: winter diets of cave hibernating bats in the United States

Abstract

Temperate bat species use extended torpor to conserve energy when ambient temperatures are low and food resources are scarce. Previous research suggests that migratory bat species and species known to roost in thermally unstable locations, such as those that roost in trees, are more likely to remain active during winter. However, hibernating colonies of cave roosting bats in the southeastern United States may also be active and emerge from caves throughout the hibernation period. We report what bats are eating during these bouts of winter activity. We captured 2,044 bats of 10 species that emerged from six hibernacula over the course of 5 winters (October–April 2012/2013, 2013/2014, 2015/2016, 2016/2017, and 2017/2018). Using Next Generation sequencing of DNA from 284 fecal samples, we determined bats consumed at least 14 Orders of insect prey while active. Dietary composition did not vary among bat species; however, we did record variation in the dominant prey items represented in species’ diets. We recorded Lepidoptera in the diet of 72.2% of individual Corynorhinus rafinesquii and 67.4% of individual Lasiurus borealis. Diptera were recorded in 32.4% of Myotis leibii, 37.4% of M. lucifugus, 35.5% of M. sodalis and 68.8% of Perimyotis subflavus. Our study is the first to use molecular genetic techniques to identify the winter diet of North American hibernating bats. The information from this study is integral to managing the landscape around bat hibernacula for insect prey, particularly in areas where hibernating bat populations are threatened by white-nose syndrome.

Winter torpor expression varies in four bat species with differential susceptibility to white-nose syndrome

“…Interestingly, M. leibii maintained the highest T sk during both torpor and arousal and were consistently active throughout the life of the transmitter. Data from winter captures and diet analysis from this region indicate M. leibii arouse from torpor regularly and engage in foraging throughout the hibernation period, frequently leaving hibernacula on winter nights, when temperatures are greater than − 1 ℃ 20 , 27 . This species is known to occupy a large portion of eastern North America, with the northern extent of its limit in southern Canada 50 .…”

“…Myotis grisescens are year-round cave dwellers that are large-bodied and highly gregarious, hibernate in cold microclimates, and can be active throughout winter 20 , 60 . Dietary analysis of M. grisescens guano collected from active bats during winter indicates that this species is regularly eating aquatic insects through the hibernation period, likely from waterways in or near hibernacula that provide ample foraging opportunities year-round 27 . Coupled with adequate energy intake throughout winter, the physical and behavioral traits of M. grisescens may enable this species to resist or tolerate Pd infections with minimal adverse effects on survival, much like M. leibii 20 , 53 .…”

“…Periodic arousal from hibernation has been hypothesized as one mechanism that may influence a species’ susceptibility to WNS 10 , 23 , 24 , 26 . Although repeated arousals from torpor can be detrimental to individuals infected by Pd , occasional arousals in regions where winters are less severe may enable populations of some species to persist 10 , 23 , 27 . Episodic activity during winter raises body temperature, often above the optimal growth range of the fungus (~ 12.5–15.8 °C) , and increases immune function, potentially inciting immune defense against Pd 28 – 32 .…”

Biomarker Metabolites Discriminate between Physiological States of Field, Cave and White-nose Syndrome Diseased Bats

“…Southern bats, unlike northern species of insectivorous bats, commonly fly out of the cave to feed during warmer winter periods, detected by cave bats via lower cave barometric pressure. This winter feasting activity requires energetically costly arousals that consume some fat reserves, but presumably result in a net energy gain if sufficient insects are consumed during these feeding bouts [ 70 , 71 ]. Some cave bats regularly fly to new locations within caves to find better conditions for hibernating sites (with different temperature or humidity conditions).…”

Emergence activity at hibernacula differs among four bat species affected by white‐nose syndrome

“…This episodic activity also raises body temperature, activating the immune system, and possibly slowing Pd growth, potentially resulting in milder infections (Prendergast et al, 2002; Dobony et al, 2011; Rowley & Alford, 2013; Verant et al, 2014). Furthermore, activities during arousals likely include drinking and foraging, which could help individuals combat some of the major effects of WNS infection, such as dehydration and starvation (Bernard et al, 2021; Cheng et al, 2019; Reynolds et al, 2017; Verant et al, 2014).…”