Work

Controlled hyperthermia by flying-foxes in the wild: understanding mammalian tolerance to hotter summer conditions

Year: 2025

Type: article

Abstract: Extreme heat events increasingly challenge the thermoregulatory capacities of wildlife, as the frequency, intensity, and duration of these events rise under climate change. Biologging can reveal the physiological and behavioural responses of wild animals to natural variation in environmental conditions, but few studies have recorded thermoregulatory patterns during extreme heat events. Flying-foxes ( Pteropus spp.) are convenient bioindicators of the impacts of extreme heat events on wildlife because they often roost in accessible colonies in trees where population-level consequences, including mass mortalities, can be readily observed. To understand how flying-foxes thermoregulate in response to extreme heat, we used implanted temperature-sensitive transmitters to record the core body temperature (T b ) of 17 free-living, adult male grey-headed flying-foxes ( Pteropus poliocephalus ) on 142 days across two Austral summers, including six days when air temperature (T a ) exceeded 42 °C and thousands of flying-foxes died. Flying-foxes exhibited daily heterothermy, with a decrease in T b after dawn (minimum: 35.9 ± 0.1 °C; absolute: 31.1 °C) followed by an increase in T b during the day (maximum: 38.7 ± 0.2 °C; absolute: 44.3 °C). Above T a of 29.5 °C, bats allowed T b to rise above normal levels (i.e., controlled hyperthermia). On extreme heat days (T a > 42 °C), T b increased by up to 6 °C to a daily maxima between 40.5 to 42.4 °C, and, consequently, T a did not exceed T b until reaching 40 °C, which is 2.5 °C higher than without controlled hyperthermia. Large variation in T b , as exhibited by grey-headed flying-foxes, reduces the physiological costs of exposure to thermal conditions in summer. Controlled hyperthermia during extreme heat events increases the range of T a , allowing non-evaporative heat loss and hence decreases water loss. The ability to manage elevated T b and high rates of evaporative water loss will shape the resilience of many mammals to future extreme heat events.

Source: Journal of Thermal Biology

DOI: 10.1016/j.jtherbio.2025.104153