Samantha Yabsley

Candidature

PhD Candidate

Thesis Title

The impacts of extreme heat events on Australian flying-foxes

Research Project

Extreme heat events are predicted to increase in frequency and duration with ongoing climate change, yet relatively little is known about the impacts of extreme heat events on wildlife populations, particularly for terrestrial vertebrates. This difficulty likely stems from the sporadic and unpredictable nature of extreme heat events, and that many species are reclusive and inconspicuous in the landscape making it difficult to document the impacts spatiotemporally.
Flying-foxes (Pteropus spp.) have emerged as an ideal model for studying the impacts of extreme heat events because the effects are relatively easy to observe; they are highly social and conspicuous, roosting colonially in exposed canopy tree branches during the day. This makes them useful bioindicators for inferring the impacts on other more-cryptic wildlife species. In addition, flying-foxes perform an essential role in maintaining the genetic diversity of native forests via long-distance pollination and seed dispersal, and as such they reflect the health of the ecosystems they exist in.  
Previous research on Australian flying-foxes has indicated that exposure to air temperatures > 42°C is highly correlated with mortality, with many extreme heat events leading to the death of thousands, or even tens of thousands of individuals in a single day. However, there appears to be variation in local exposure to extreme heat events, and previous research indicates within- and between- species differences in sensitivity to heat stress. Gaining a better understanding of the drivers of exposure and sensitivity to heat stress is essential to developing targeted and effective heat stress mitigation.
To help mitigate the worst of the impacts on flying-foxes in Australia, some wildlife rehabilitators and land managers rely on sprinklers to cool the roost microclimate and the animals with water. Yet, the consequences of the use of sprinklers on the roost microclimate, animal physiology and behaviour have not been formally tested. In the absence of published scientific evidence, there are concerns that under certain circumstances, these well-intentioned strategies may actually exacerbate heat stress by a) increasing relative humidity which is known to impair evaporative heat loss in other mammals, or b) the use of sprinklers could potentially startle the animals and cause them to move to less thermally favourable areas of the roost that are more exposed to the heat.
During my candidature, I aim to conduct spatial analyses to better understand the historical, current and future exposure of the Pteropus genus to extreme heat events globally, and to rank the known Australian flying-fox roosts by their risk of exposure to extreme heat. I aim to better understand the environmental conditions that cause heat stress in each of Australia’s mainland species by investigating the temperature and humidity onsets for thermoregulatory behaviours as a proxy for heat stress. I also aim to provide the much-needed evidence base for the use of sprinklers in heat stress mitigation, by studying the effects of the sprinklers on roost microclimate and flying-fox behaviour under a range of ambient starting conditions including during extreme heat events. I also aim to build upon an existing population model to determine the implications of extreme heat events on the long-term persistence of Australian flying-foxes.
The research outcomes will be directly useful to land managers for prioritising ‘at risk’ flying-fox roosts, more precisely predict where heat stress and mortality will occur and which species will be most vulnerable, and provide the much-needed evidence base for the use of sprinklers in heat stress mitigation.

Website https://www.animalecologylab.org/samantha-yabsley.html

Publications

Meade J, McCarthy ED, Yabsley SH, Grady SC, Martin JM, Welbergen JA, (2025) 'Using Night-Time Drone-Acquired Thermal Imagery to Monitor Flying-Fox Productivity—A Proof of Concept', Remote Sensing, 17(3), art. no. 518

Yabsley, S. H., Meade, J., Hibburt, T., Martin, J. M., Boardman, W. S. J., Nicolle, D., Walker, M., Turbill, C & Welbergen, J. A. (2022). Variety is the spice of life: flying-foxes exploit a variety of native and exotic food plants in an urban landscape mosaic. Frontiers in Ecology and Evolution, 10:907966

Yabsley, S. H., Meade, J., Martin, J. M., & Welbergen, J. A. (2021). Human-modified landscapes provide key foraging areas for a threatened flying mammal: The grey-headed flying-fox. Plos One, 16: e0259395.

Supervisors

Professor Justin Welbergen, Dr Jessica Meade, A/Professor Chris Turbill.