Australian flying fox die-offs

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.

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

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. On occasion, the federally endangered spectacled flying fox (Pteropus conspicillatus) may be affected as well, further threatening the species in Australia.

Impacts on demography

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

Impacts on behaviour
Main article: Bat § Thermoregulation

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 bases of trees where they form piles of lethargic and dead bats.

List of recorded Australian flying fox die-offs
EventDateStateAreaNumber of camps affectedMinimum mortality estimateMaximum mortality estimateSpecies affectedSource
1February 1791NSWSydneygrey-headed flying foxTench 1793[1][2]
2December 1905NSWHelidongrey-headed flying foxRatcliffe, 1932[1][3]
3January 1913NSWMallanganeegrey-headed flying foxRatcliffe, 1932[1][3]
4January 1994QldTownsville and Ipswich21000grey-headed flying fox, black flying foxWelbergen et al., 2008[4]
5December 1994NSWCabramatta and Gordon260006000grey-headed flying foxWelbergen et al., 2008[4]
6late 1900sNT12929grey-headed flying foxTidemann & Nelson 2011[4]
7January 2000QldIpswich500500grey-headed flying fox, black flying foxWelbergen et al., 2008[4]
812 January 2002NSWMurwillumbah93679grey-headed flying fox, black flying foxWelbergen, Klose et al., 2008[4]
9January 2003NSWCabramatta and Gordon250005000grey-headed flying foxWelbergen et al., 2008[4]
10January 2004NSWBellingen130008000grey-headed flying foxWelbergen et al., 2008[4]
11December 2004NSWCoff's Harbour210005000grey-headed flying foxWelbergen et al., 2008[4]
12December 2005Qld, NSW, Vic356138900grey-headed flying fox, black flying foxWelbergen et al., 2008[4]
13January 2006NSW, Vic642734843grey-headed flying foxWelbergen et al., 2008[4]
14December 2006 to January 2007VicMelbourne2207207grey-headed flying foxWelbergen et al., 2008[4]
15January 2014Qld>25100000grey-headed flying fox, black flying foxMurphy 2014, Saunders 2014[4]
16November 2014NSWCasino and Richmond Valley270007000grey-headed flying fox, black flying foxGodfrey 2014[4]
17November 2018Qld3300040000spectacled flying fox, black flying fox[5]
18December 2019VicMelbourne4500grey-headed flying fox[6][7]

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 (PDF). 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. doi:10.2307/993. JSTOR 993.
  4. Thomas J. O'Shea; Paul M. Cryan; David T.S. Hayman; Raina K. Plowright; Daniel G. Streicker (2016). "Multiple mortality events in bats: a global review". Mammal Review. 46 (3): 175–190. doi:10.1111/mam.12064. PMC 5942905. PMID 29755179.
  5. https://www.bbc.com/news/world-australia-46859000
  6. "Flying foxes are dying en masse in Australia's extreme heat". Animals. 7 January 2020.
  7. "Heat stress and the Australian flying fox". BBC News. 24 January 2020.
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