Hot bats: extreme thermal tolerance in a desert heat wave

Abstract

Climate change is predicted to increase temperature extremes and thus thermal stress on organisms. Animals living in hot deserts are already exposed to high ambient temperatures (T a) making them especially vulnerable to further warming. However, little is known about the effect of extreme heat events on small desert mammals, especially tree-roosting microbats that are not strongly protected from environmental temperature fluctuations. During a heat wave with record T as at Sturt National Park, we quantified the thermal physiology and behaviour of a single free-ranging little broad-nosed (Scotorepens greyii, henceforth Scotorepens) and two inland freetail bats (Mormopterus species 3, henceforth Mormopterus) using temperature telemetry over 3 days. On 11 and 13 January, maximum T a was ∼45.0 °C, and all monitored bats were thermoconforming. On 12 January 2013, when T a exceeded 48.0 °C, Scotorepens abandoned its poorly insulated roost during the daytime, whereas both Mormopterus remained in their better insulated roosts and were mostly thermoconforming. Maximum skin temperatures (T skin) ranged from 44.0 to 44.3 °C in Scotorepens and from 40.0 to 45.8 °C in Mormopterus, and these are the highest T skin values reported for any free-ranging bat. Our study provides the first evidence of extensive heat tolerance in free-ranging desert microbats. It shows that these bats can tolerate the most extreme T skin range known for mammals (3.3 to 45.8 °C) and delay regulation of T skin by thermoconforming over a wide temperature range and thus decrease the risks of dehydration and consequently death.

Surface reflectance drives nest box temperature profiles and thermal suitability for target wildlife

“…Ambient summer temperatures during this study were relatively mild for southeast Australia; for example, Melbourne reached 45.1°C on 19 December 2015 [45]. Our findings suggest that on extremely hot days such as these, endothermic animals occupying all boxes are likely to experience significant thermal stress [29,65], potentially forcing them to vacate boxes [57,66], thereby increasing predation risk [67]. This is likely to have a significant negative influence on the fitness of animals occupying nest boxes compared to those in natural hollows during summer.…”

Modelling mammalian energetics: the heterothermy problem

“…, with corresponding skin temperatures up to 45.8°C [76]. In general, however, our capacity to model mammalian responses to high T a is hindered by a general lack of understanding of upper limits in T a tolerance and how flexible they are [2,8,12,77].…”

No phenotypic plasticity in nest-site selection in response to extreme flooding events

“…By contrast, consideration of phenotypic plasticity as a response to ECEs has been mostly theoretical [9][10][11][12]. Phenotypic plasticity may allow individuals to respond pre-emptively to upcoming ECEs or adapt once the extreme conditions arise through behavioural or physiological change [12][13][14]. To pre-empt future ECEs, individuals must possess a reliable cue to predict future conditions [15].…”