Flying-fox colonies, extreme heat events and the need for empirically tested intervention methods: towards a temperature-humidity index for the Grey-headed Flying-fox <i>Pteropus poliocephalus</i>

ABSTRACT Numerous intervention methods are used to mitigate flying-fox mortalities during extreme heat events, which range from administering assistance to individuals to roost-scale interventions. However, there is little scientific evidence supporting most of these interventions, limiting interpretations of efficacy to anecdotes. In 2020, the NSW Government initiated a collaborative research trial with Western Sydney University and Campbelltown City Council to investigate the effects of sprinklers on roost microclimate and behavioural responses in the Grey-headed Flying-fox Pteropus poliocephalus. A sprinkler system for two treatment sites within a flying-fox roost was designed pro bono by an agricultural engineer and installed through a donation from World Animal Protection, with wildlife carers from Sydney Metropolitan Wildlife Services providing on-ground support. A key aim of this work is to establish a temperature-humidity index for the Grey-headed Flying-fox to enable identification of temperature-humidity thresholds for safe interventions. After four summers, only a single day of extreme heat has occurred, during which flying-foxes unusually roosted away from both treatment sites and the control site. Preliminary findings are promising, but the research trial needs more summers to collect more substantial data, especially observation of flying-foxes’ responses to the sprinklers during extreme heat conditions.