Temperatures below leaf litter during winter prescribed burns: implications for litter-roosting bats

Abstract

Some bat species, including eastern red bats (Lasiurus borealis), roost for short periods beneath leaf litter on the forest floor during winter in the south-eastern USA, a region subjected to frequent fire. The variability in fuel consumption, the heterogeneous nature of burns, and the effects of litter and duff moisture on forest-floor temperatures during winter burning could influence potential survival for bats beneath the leaf litter if they are unable to escape on-coming flames. We measured temperatures below leaf litter in 64 south-slope plots during nine controlled burns in the Ouachita Mountains of Arkansas to determine the probability of survival. Maximum temperature recorded under leaf litter at each plot averaged 292°C (±20 s.e.) and ranged from 10 to 717°C. Only three (5%) of the plots experienced temperatures that were deemed survivable (<60°C sustained for 60 s) during burns on warmer winter days (air temperatures 15.0–26.1°C). Temperatures below the leaf litter measured just before the arrival of fire (average = 19.6°C) suggested that if bats were roosting in plots they would have been in shallow torpor, which would have enabled faster escape from approaching flames. Burning during the warmer periods of winter (e.g. ≥15°C) and during afternoons could potentially improve survival by bats roosting under leaf litter by reducing arousal and escape times.

A new cue for torpor induction: charcoal, ash and smoke

“…Interestingly, in these two species, smoke was sensed even by torpid individuals and induced rapid arousal, whereas none of the antechinus were still torpid when smoke was introduced in the present study. Arousal from torpor in response to smoke has also been recorded in bats (Scesny, 2006) and it is possible that fire cues other than smoke may influence activity and arousal from torpor, such as an increase in T a or changes in humidity (Dickinson et al, 2010;Perry and McDaniel, 2015). Regardless, it is likely that smoke is perceived as a warning signal and will elicit an escape response in both torpid and normothermic small mammals, therefore strengthening the chances of surviving an approaching fire front provided a secure shelter can be found in time.…”

“…Further, the third activity bout in the afternoon (in addition to two activity bouts at night) started in response to smoke at a time when the animals would not have known whether they would be fed or not; therefore, this emergency response was not food related. The intrusion of smoke into a nest site would indicate the vulnerability of this particular site to fire and heat (Dickinson et al, 2010;Perry and McDaniel, 2015), probably causing animals to retreat into a more secure shelter. In our experimental setup, such secure sites like underground burrows or rocky crevices (Howard et al, 1959) were not provided, perhaps explaining the protracted length of the activity bout following smoke exposure.…”

“…The physiological and behavioural responses of individual mammals to fire have attracted some recent scientific attention (Scesny, 2006;Dickinson et al, 2010;Doherty et al, 2015;Perry and McDaniel, 2015;Doty et al, 2016;Matthews et al, 2016;Nowack et al, 2016a;Stawski et al, 2016). For example, volant bats employed less torpor, characterised by reduced metabolic rate and body temperature (T b ), shortly after a wildfire in comparison to 2 years later (Doty et al, 2016).…”

Bats in a changing landscape: Linking occupancy and traits of a diverse montane bat community to fire regime

“…Myotis evotis, the only species in our study area for which roosting preferences with relation to fire have been studied, selected roosts away from burned areas (Snider, Cryan, & Wilson, 2013). High severity fire destroys canopy, hence reducing roost availability for foliage roosting species like L. cinereus and L. blossevillii; fire may also cause direct mortality of these species if it occurs during winter when they may roost within leaf litter (Johnston & Whitford, 2009;Perry & McDaniel, 2015). However, many of the species in our study area use snags, hollows, crevices, and exfoliating bark to roost, structures that may be created or enhanced by fire (Johnson, Edwards, Ford, & Gates, 2009;O'Keefe & Loeb, 2017).…”

Physiological and behavioral responses of an arboreal mammal to smoke and charcoal-ash substrate

“…Small ground-dwelling mammals as well as some bat species enter torpor beneath leaf litter on the forest floor and might not be able to respond to a fast spreading fire (Perry 2012;Perry and McDaniel 2015). Therefore, terrestrial animals are likely to be more affected by even low intensity fires than arboreal mammals, which may be out of reach of the fire in their tree hollows, unless the fire scorches the canopy.…”