Bat thermoregulation in the heat: Limits to evaporative cooling capacity in three southern African bats

Czenze, Zenon J.; Naidoo, S.; Kotzé, Antoinette; McKechnie, Andrew E.

doi:10.1016/j.jtherbio.2020.102542

Cited by 19 publications

(18 citation statements)

References 52 publications

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“…While 40°C may be a good benchmark for assessing baseline heat stress risk for bat boxes, thermal tolerance likely varies within and among species (Ancillotto et al, 2018; Czenze, Naidoo, Kotze, & McKechnie, 2020; Henshaw & Folk Jr., 1966; Licht & Leitner, 1967). Furthermore, thermoregulatory strategies may change with latitude (Czenze, Brigham, Hickey, & Parsons, 2017; Dunbar & Brigham, 2010; Encarnação, Otto, & Becker, 2012), which may affect regional intraspecific heat tolerance.…”

Section: Thermal Tolerance Of Temperate Batsmentioning

confidence: 99%

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes

Crawford

O’Keefe

2021

Conservat Sci and Prac

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Bat boxes are commonly deployed to mitigate the loss of bat roosting habitat. Due to a dearth of microclimate research, numerous untested commercially available bat boxes, and the uncertain impacts of a rapidly changing climate, the overheating risk presented to bats by bat boxes is largely unquantified. Based on limited research, we know many boxes overheat (i.e., temperatures >40 C). A lack of standardized protocols to evaluate microclimate and misleading information available to the public leads to a murky understanding of risks involved with deploying bat boxes. Herein, we evaluate the thermal tolerance of temperate-zone bats, delineate areas of concern regarding the risks to temperate-zone bats when bat boxes are deployed, identify strategies for reducing overheating risk, suggest methods for assessing microclimate, and provide a visual framework to assess overheating risk. Identifying suitable design and placement combinations is crucial to developing region-specific strategies to mitigate against overheating. We urge consideration of the risks involved with using bat boxes, advocate for rigorous testing before deployment, and suggest using alternatives when possible.

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Section: Thermal Tolerance Of Temperate Batsmentioning

confidence: 99%

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes

Crawford

O’Keefe

2021

Conservat Sci and Prac

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“…under roofs; Kunz & Lumsden, 2003). There is some evidence that variation in heat tolerance among sympatric species is correlated with the thermal properties of roosts, with species experiencing hotter T roost possessing higher heat tolerance limits and evaporative cooling capacity (Bronner et al, 1999;Cory Toussaint & McKechnie, 2012;Czenze, Naidoo, et al, 2020;Marom et al, 2006;Minnaar et al, 2014;Noakes et al, 2021). Here, we test the hypothesis that bat heat tolerance and evaporative cooling capacity have co-evolved with roost preferences.…”

Section: Introductionmentioning

confidence: 95%

“…Evaporative cooling is the only avenue for heat dissipation available to bats when T roost > T b , with evaporative water losses constituting as much as 80%-85% of overall water flux (Arad & Korine, 1993;Studier, 1970). Several authors have examined bat thermal physiology and roost preferences in tropical and subtropical regions (Bronner et al, 1999;Churchill, 1991;Churchill et al, 1997;Cory Toussaint & McKechnie, 2012;Czenze, Naidoo, et al, 2020;López-Baucells et al, 2017;Maloney et al, 1999;McDonald et al, 1990;Monadjem, 2005;Turbill, Körtner, et al, 2003;Turbill, Law, et al, 2003), where most bat diversity is found. However, data collected under standardized conditions for many more species are needed to evaluate how bat thermal physiology has evolved with roost preferences, the role of thermal physiology in determining species' habitat requirements and the capacity of tropical and subtropical bats to respond to rapid anthropogenic global heating (IPCC, 2021).…”

Section: Introductionmentioning

confidence: 99%

Caves, crevices and cooling capacity: Roost microclimate predicts heat tolerance in bats

et al. 2021

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1. The microsites that animals occupy during the rest phase of their circadian activity cycle influence their physiology and behaviour, but relatively few studies have examined correlations between interspecific variation in thermal physiology and roost microclimate. Among bats, there is some evidence that species exposed to high roost temperatures (T roost ) possess greater heat tolerance and evaporative cooling capacity, but the small number of species for which both thermal physiology and roost microclimate data exist mean that the generality of this pattern remains unclear.2. Here, we test the hypothesis that bat heat tolerance and evaporative cooling capacity have co-evolved with roost preferences. We predicted that species occupying roosts poorly buffered from high outside environmental temperature exhibit higher heat tolerance and evaporative cooling capacity compared to species inhabiting buffered roosts in which T roost remains well below outside conditions.3. We used flow-through respirometry to investigate thermoregulation at air temperatures (T a ) approaching and exceeding normothermic body temperature (T b ) among six species with broadly similar body mass but differing in roost microclimate (hot vs. cool roosts). We combined these data with empirical measurements of T roost for each study population.4. Hot-roosting species tolerated T a ~4°C higher than cool-roosting bats before the onset of loss of coordinated locomotion and non-regulated hyperthermia. The evaporative scope (i.e. ratio of maximum evaporative water loss [EWL] to minimum thermoneutral EWL) of hot-roosting species (16.1 ± 2.4) was substantially higher than that of cool-roosting species (5.9 ± 2.4). Maximum evaporative cooling capacities (i.e. evaporative heat loss/metabolic heat production) of hot-roosting species were >2, while the corresponding values for cool-roosting species were ≤1.5. The greater heat tolerance and higher evaporative cooling capacity of hotroosting species compared with those occupying cooler roosts reveal variation in bat evaporative cooling capacity correlated with roost microclimate, supporting the hypothesis that thermal physiology has co-evolved with roost preference.

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“…They reach their thermal limits when body temperature approaches 41-44°C due to overheating or dehydration [3,4]. The maximum temperatures experienced by mammals are increasing because of extensive habitat modification [5] or more frequent and more intense heatwaves associated with global climate change [6], and these maxima can be fatal [7][8][9][10][11]. Indeed, heatwaves have led to several recent mass mortalities of flying foxes (Pteropus spp.)…”

Section: Introductionmentioning

confidence: 99%

“…By accumulating heat instead of dumping it and thereby tolerating an increase in body temperature, the need for evaporative cooling can be postponed or even avoided, and considerable amounts of water can be conserved [15,16]. The classic example of this adaptive hyperthermia comes from dromedary camels (Camelus dromedarius), which regularly cycle between 41°C in daytime and 34-35°C at night when dehydrated [17], but other mammals also allow hyperthermia during hot phases (llamas [18], elephants [19], large treeshrews [20], ringtail possums [11], bats [7,16,21]).…”

Section: Introductionmentioning

confidence: 99%

Tropical bats counter heat by combining torpor with adaptive hyperthermia

Reher

Dausmann

2021

Proc. R. Soc. B.

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Many tropical mammals are vulnerable to heat because their water budget limits the use of evaporative cooling for heat compensation. Further increasing temperatures and aridity might consequently exceed their thermoregulatory capacities. Here, we describe two novel modes of torpor, a response usually associated with cold or resource bottlenecks, as efficient mechanisms to counter heat. We conducted a field study on the Malagasy bat Macronycteris commersoni resting in foliage during the hot season, unprotected from environmental extremes. On warm days, the bats alternated between remarkably short micro-torpor bouts and normal resting metabolism within a few minutes. On hot days, the bats extended their torpor bouts over the hottest time of the day while tolerating body temperatures up to 42.9°C. Adaptive hyperthermia combined with lowered metabolic heat production from torpor allows higher heat storage from the environment, negates the need for evaporative cooling and thus increases heat tolerance. However, it is a high-risk response as the torpid bats cannot defend body temperature if ambient temperature increases above a critical/lethal threshold. Torpor coupled with hyperthermia and micro-torpor bouts broaden our understanding of the basic principles of thermal physiology and demonstrate how mammals can perform near their upper thermal limits in an increasingly warmer world.

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Bat thermoregulation in the heat: Limits to evaporative cooling capacity in three southern African bats

Cited by 19 publications

References 52 publications

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes

Caves, crevices and cooling capacity: Roost microclimate predicts heat tolerance in bats

Tropical bats counter heat by combining torpor with adaptive hyperthermia

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