Infrared insights: behavioural and environmental heat loss strategies in flying-foxes

Thermal resilience in animals under heat stress depends on both behaviour and access to thermally favourable microhabitats. In grey-headed flying-foxes (Pteropus poliocephalus), behaviours such as licking and pressing against tree trunks are assumed to promote evaporative and conductive heat loss, but their thermal effects remain poorly quantified. We used thermal imaging across four hot days (air temperature [Ta] range: ~31 to 39 °C), capturing 110 thermographs of 325 individuals. Surface temperatures (Ts) of bats and trees were compared to assess thermoregulatory patterns. Bats hanging from trees approached thermal equivalence with tree surfaces at high Ta (~39 °C), while bats pressed on branches or trunks maintained a greater differential (~2.4 °C), indicating posture-specific heat gain. The Ts varied significantly by body part; the dorsal surface was warmest, while the thumb and radius were coolest and increased least with rising Ta. These Ts were further distinguished by licking that significantly reduced Ts across licked and unlicked body surfaces (~2 °C), independent of body part. These findings provide direct evidence that tree-pressing and licking behaviours aid in heat management for flying-foxes experiencing hot environmental conditions.