Microclimatic drivers of thermoregulatory behaviour in Spectacled Flying Foxes

Air temperature is the number managers use to predict heat risk for flying foxes, and it is not enough. I watched spectacled flying foxes in their daytime roosts and recorded what each animal did. At the same time I measured air temperature, wind, humidity and solar radiation. Temperature predicted whether an animal was thermoregulating at all.

It did not predict the expensive behaviour. The escalation to active fanning followed intense solar radiation, interacting with temperature. Heat vulnerability is a microclimate problem, so a warning built on air temperature alone will miss the worst hours.

Original abstract as submitted

Climate change is exerting profound impacts on biodiversity, but these effects are often mediated by physiological constraints that influence the ecological and demographic performance of species. To predict and anticipate emerging threats, it is critical to understand the environmental drivers that trigger physiological stress responses in vulnerable species. In this study, we investigated the thermoregulatory behaviour of the Spectacled Flying Fox (Pteropus conspicillatus), a species increasingly affected by extreme heat events. Through focused behavioural observations, we tracked individual flying foxes’ thermoregulatory behaviour in their daytime roosts while simultaneously recording key microclimatic variables, including air temperature, wind speed, humidity, and metrics of solar radiation intensity and exposure. Our analyses reveal that while ambient temperature is a strong predictor of thermoregulatory activity, it only partially explains the escalation to high-cost behaviours such as active fanning. Instead, intense solar radiation emerged as a pivotal factor, interacting with temperature to drive behavioural transitions. These results highlight that physiological stress in spectacled flying foxes —and therefore their vulnerability to heatwaves—is governed by a complex interplay of microclimatic conditions, rather than temperature alone. Understanding these mechanisms is essential to improving predictions of climate change impacts and informing conservation strategies for vulnerable species.