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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

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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

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

Impacts on behaviour

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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

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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]
4 January 1994 Qld Townsville and Ipswich 2 1000 grey-headed flying fox, black flying fox Welbergen et al., 2008[4]
5 December 1994 NSW Cabramatta and Gordon 2 6000 6000 grey-headed flying fox Welbergen et al., 2008[4]
6 late 1900s NT 1 29 29 grey-headed flying fox Tidemann & Nelson 2011[4]
7 January 2000 Qld Ipswich 500 500 grey-headed flying fox, black flying fox Welbergen et al., 2008[4]
8 12 January 2002 NSW Murwillumbah 9 3679 grey-headed flying fox, black flying fox Welbergen, Klose et al., 2008[4]
9 January 2003 NSW Cabramatta and Gordon 2 5000 5000 grey-headed flying fox Welbergen et al., 2008[4]
10 January 2004 NSW Bellingen 1 3000 8000 grey-headed flying fox Welbergen et al., 2008[4]
11 December 2004 NSW Coff's Harbour 2 1000 5000 grey-headed flying fox Welbergen et al., 2008[4]
12 December 2005 Qld, NSW, Vic 3 5613 8900 grey-headed flying fox, black flying fox Welbergen et al., 2008[4]
13 January 2006 NSW, Vic 6 4273 4843 grey-headed flying fox Welbergen et al., 2008[4]
14 December 2006 to January 2007 Vic Melbourne 2 207 207 grey-headed flying fox Welbergen et al., 2008[4]
15 January 2014 Qld >25 100000 grey-headed flying fox, black flying fox Murphy 2014, Saunders 2014[4]
16 November 2014 NSW Casino and Richmond Valley 2 7000 7000 grey-headed flying fox, black flying fox Godfrey 2014[4]
17 November 2018 Qld 33000 40000 spectacled flying fox, black flying fox [5]
18 December 2019 Vic Melbourne 4500 grey-headed flying fox [6][7]

References

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  1. ^ a b c d e f g 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. ^ a b 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. ^ a b c d e f g h i j k l m 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. ^ "How one heatwave killed 'a third' of a bat species in Australia". BBC News. 15 January 2019.
  6. ^ "Flying foxes are dying en masse in Australia's extreme heat". Animals. 7 January 2020. Archived from the original on 8 January 2020.
  7. ^ "Heat stress and the Australian flying fox". BBC News. 24 January 2020.
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