Heatwaves are now hotter, longer and more frequent than 50 years ago, and this trend is set to continue under anthropogenic climate change (Cowan et al., 2014). Extreme heat events are well known to result in substantial die-offs in flying-fox populations (Mo et al., 2021; Ratnayake et al., 2019; Welbergen et al., 2008), with many tens of thousands of black, grey-headed and spectacled flying-foxes having succumbed due to heat stress across SA, Vic, NSW, & Qld during the past decade alone.
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A now-common intervention aimed to help mitigate the worst of the impacts of extreme heat events on flying-foxes involves ‘spraying’ (or ‘misting’) of the roost environment. This practice is known to reduce ambient temperatures via evaporative cooling; however, it can also increase humidity, and under extreme conditions this is known to reduce the effectiveness of animal thermoregulatory mechanisms (e.g., Cooper and Withers, 2008; Kurta, 2014; Lasiewski et al., 1966; Procter and Studier, 1970; Webb et al., 1995), and so risks exacerbating heat stress. The combined effects of spraying on roost temperature and humidity, and hence flying-fox heat stress, have not been formally assessed, impeding the development of effective heat stress interventions (Mo and Roache, 2020).
To address this, we are undertaking a project in which we: i) map temperature and humidity across roosts subject to spraying, to quantify explicitly the effects of spraying on a roost’s microclimatic conditions; and ii) collect behavioural and physiological data on thermoregulatory behaviours in response to the (altered) microclimatic conditions, to construct a temperature-humidity index (‘heat stress index’) for flying-foxes. In combination, these approaches enable us to infer and validate the efficacy of spraying on flying-fox heat stress and establish much-needed temperature-humidity thresholds for intervention.
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AIM: The aim of this project is to validate the efficacy of spraying for mitigating flying-fox heat stress and to establish much-needed temperature-humidity thresholds for intervention.
RESEARCH UMBRELLA: Flying-foxes and extreme heat events
TEAM: Prof Justin Welbergen (WSU); Dr Christopher Turbill (WSU) Dr Jessica Meade (WSU); Dr John Martin (Ecosure); Dr Annabel Dorrestein (Tel-Aviv University; WSU), Eliane McCarthy (University of Sydney; WSU), Samantha Yabsley (WSU)
PARTNERS: Matthew Mo, Elisabeth Timmiss (NSW DPE)
References
- RATNAYAKE, H. U., WELBERGEN J.A., VAN DER REE, R & KEARNEY, M. R. (2021) Variation in fur properties may explain differences in heat-related mortality among Australian flying-foxes. Australian Journal of Zoology, 68:285-295
- MO, M., ROACHE, M., DAVIES, J., HOPPER, J., PITTY, H., FOSTER, N., ... & WELBERGEN, J. A. (2021). Estimating flying-fox mortality associated with abandonments of pups and extreme heat events during the austral summer of 2019–20. Pacific Conservation Biology. doi: 10.1071/PC21003
- RATNAYAKE, H. U., KEARNEY, M, R., GOVEKAR, P., KAROLY, D. & WELBERGEN, J. A. (2019) Forecasting wildlife die-offs from extreme heat events. Animal Conservation, 22(4): 386-395. DOI: 10.1111/acv.12476
- WELBERGEN J. A., BOOTH, C. and MARTIN, J. Killer climate: tens of thousands of flying foxes dead in a day. The Conversation, 24-2-14
- WELBERGEN, J. A. (2012) Impacts of extreme events on biodiversity – lessons from die-offs in flying-foxes. Proceedings of the International Symposium on the importance of Bats as Bioindicators. Granollers, Barcelona. ISBN: 978-84-87790-69-0
- WELBERGEN, J. A., KLOSE, S. M., MARKUS, N. & EBY, P. (2008) Climate change and the effects of temperature extremes on Australian flying-foxes. Proceedings of the Royal Society of London, Series B 275, 419-425