A burning question: what are the risks and benefits of mammalian torpor during and after fires?

Abstract

Although wildfires are increasing globally, available information on how mammals respond behaviourally and physiologically to fires is scant. Despite a large number of ecological studies, often examining animal diversity and abundance before and after fires, the reasons as to why some species perform better than others remain obscure. We examine how especially small mammals, which generally have high rates of energy expenditure and food requirements, deal with fires and post-fire conditions. We evaluate whether mammalian torpor, characterised by substantial reductions in body temperature, metabolic rate and water loss, plays a functional role in survival of mammals impacted by fires. Importantly, torpor permits small mammals to reduce their activity and foraging, and to survive on limited food. Torpid small mammals (marsupials and bats) can respond to smoke and arouse from torpor, which provides them with the possibility to evade direct exposure to fire, although their response is often slowed when ambient temperature is low. Post-fire conditions increase expression of torpor with a concomitant decrease in activity for free-ranging echidnas and small forest-dwelling marsupials, in response to reduced cover and reduced availability of terrestrial insects. Presence of charcoal and ash increases torpor use by captive small marsupials beyond food restriction alone, likely in anticipation of detrimental post-fire conditions. Interestingly, although volant bats use torpor on every day after fires, they respond by decreasing torpor duration, and increasing activity, perhaps because of the decrease in clutter and increase in foraging opportunities due to an increase in aerial insects. Our summary shows that torpor is an important tool for post-fire survival and, although the physiological and behavioural responses of small mammals to fire are complex, they seem to reflect energetic requirements and mode of foraging. We make recommendations on the conditions during management burns that are least likely to impact heterothermic mammals.

Welcome to the Pyrocene: animal survival in the age of megafire

“…Sleepy lizards aren't alone-a growing diversity of animal species from fire-prone landscapes have been found to sense incipient fire (Geiser et al, 2018;. This capacity to detect, recognise, and respond to olfactory cues raises obvious parallels with another widespread and lethal selective force-predation.…”

“…That 13 other species in the same room did not react suggests that the sleepy lizard's response is probably not merely a generic response to novel stimuli but a fine-tuned response to a cue with a specific interpretation. While most other examples of animals responding to fire cues come from wildcaught animals (Geiser et al, 2018)-and therefore cannot distinguish between learned and innate responses-captive bred fat-tailed dunnarts (Sminthopsis crassicaudata) arouse from torpor when exposed to smoke, also suggesting an innate response (Stawski, Matthews, et al, 2015).…”

A physiological understanding of organismal responses to fire

“…However, complications may arise for the many mammalian and avian species that employ torpor (a temporal reduction in metabolic rate and body temperature) during winter in response to a decrease in temperature and resource availability. While some torpid mammals are able to respond to fi re cues such as smoke, their responses are often slowed at colder temperatures [7]. Therefore, these torpid animals would be at risk of mortality during winter management burns conducted at very cold temperatures, as they would be less likely to rewarm from torpor and escape.…”

“…Therefore, these torpid animals would be at risk of mortality during winter management burns conducted at very cold temperatures, as they would be less likely to rewarm from torpor and escape. Studies conducted in Australia also revealed that some small terrestrial mammals become energetically constrained even after mild fi res that only reduce ground cover and understorey vegetation [7]. Conversely, some bats are less energetically constrained as they are able to take advantage of the more open foraging conditions.…”

“…Promisingly, many research stations and agencies conduct experimental and management burns in numerous countries. Researchers can take advantage of these burns to ensure they obtain a robust data set, including before and after a fi re and in nearby control areas, as has been done recently in Australia [7].…”