Australian flying fox die-offs

Thermal image of a juvenile grey-headed flying fox during an extreme temperature event

In the last two decades tens of thousands of Australian flying foxes have died during extreme heat events.^[1] Flying fox die-offs feature arguably among the most dramatic mass mortality events witnessed in nature, but they can be indicators of heat stress in more cryptic fauna where impacts are more difficult to assess. The die-offs are important additional threats to Australian flying-foxes and the ecosystem services they provide, and highlight the complex implications of climate change for behaviour, demography, and species survival.

Impacts on species

Two Australian flying fox species have reportedly been affected by extreme heat events: the grey-headed flying fox (Pteropus poliocephalus) and the black flying fox (P. alecto). Where mixed-species colonies are affected the black flying fox suffers substantially higher mortality than the grey-headed flying fox.^[1] However, summer temperatures are more extreme within the range of the grey-headed flying fox than within the range of the black flying-fox, and therefore the actual total number of casualties is much higher among grey-headed flying foxes than black flying foxes.

Impacts on demography

Mortality is especially high among dependent young and lactating females, but any demographic category can be affected.^[1]

Impacts on behaviour

Observations in flying fox colonies during extreme heat events have revealed that flying foxes go through a predictable sequence of thermoregulatory behaviours with rising temperatures:^[1]

• wing-fanning
• shade-seeking and clustering
• panting
• salivation

Beyond this, individuals tend to be found near the base of trees where they form piles of lethargic and dead bats.

List of known Australian flying fox die-offs

Event	Date	State	Area	Number of camps affected	Minimum mortality estimate	Maximum mortality estimate	Species affected	Source
1	February 1791	NSW	Sydney				grey-headed flying fox	Tench 1793[1][2]
2	December 1905	NSW	Helidon				grey-headed flying fox	Ratcliffe, 1932[1][3]
3	January 1913	NSW	Mallanganee				grey-headed flying fox	Ratcliffe, 1932[1][3]

... followed by 16 recorded instances in Eastern Australia between 1994 and 2007, involving thousands of dead bats.^[1]

References

1. Justin A. Welbergen, Stefan M. Klose, Nicola Markus & Peggy Eby (2008). "Climate change and the effects of temperature extremes on Australian flying-foxes". Proceedings of the Royal Society B: Biological Sciences 275 (1633): 419–425. doi:10.1098/rspb.2007.1385. PMC 2596826. PMID 18048286.
2. Tench, Watkin (1793). Complete account of the settlement at Port Jackson; Including An Accurate Description of the Situation of the Colony; of the Natives; and Of Its Natural Productions. London: G. Nicol and J. Sewell.
3. Francis Ratcliffe (1932). "Notes on the fruit bats (Pteropus spp.) of Australia". Journal of Animal Ecology 1 (1): 32–57. JSTOR 993.

External links

• ARKive – images and movies of the grey-headed flying-fox (Pteropus poliocephalus)
• Background: P. poliocephalus
• Brief history of Megachiroptera / Megabats