Australian flying-fox numbers soaring again

The population of Australia’s vulnerable grey-headed flying-fox are bouncing back, leading scientists to be “optimistic” about the future of the species.

Grey-headed flying-foxes (Pteropus poliocephalus) are among the largest flying mammals in the world. These bats can have a wingspan of more than 1 metre. They are mostly found along Australia’s east coast from Victoria to central Queensland but are also found around the south coast as far as Adelaide.

The bats are intelligent and social. They have relatively complex communication compared to other animals, producing more than 20 different vocalisations.

These animals are also important pollinators.

Habitat clearing and adverse effects of climate change have led to a decline in numbers. Tens of thousands of flying-foxes have died in summers with pronounced heat waves, such as in 2019. They are officially listed as a vulnerable species.

But getting a handle on the numbers of the flying animals, who gather in tightly packed “camps,” has proven tricky. This was made even more difficult during COVID-19 pandemic lockdowns and the 2019–20 megafires which spread through the southeast of the continent – both making regular counts challenging or impossible.

A new census by scientists at the CSIRO has given scientists a better sense of the grey-headed flying-fox numbers and the results are encouraging. The findings are published in the public access journal PLOS ONE.

Nearly 12,000 surveys visiting 912 roosts of grey-headed flying-foxes (GHFF) from November 2012 to August 2022 are included in the analysis. The counts were taken by Australia’s National Flying-fox Monitoring Program (NFFMP)

“We found that the Vulnerable GHFF population was relatively stable over the 10-year survey period,” the authors write. “The quarterly counts fluctuated considerably, but our consistent long-term data shows that these fluctuations did not necessarily represent population changes, but expected variation in survey effort, accuracy and precision.”

Modelling suggests the stable population is about 622,000–692,000 bats.

The researchers note that the IUCN listing of flying foxes as “vulnerable” is based on an “inferred” population decline to 467,000 in November 2019, during the megafires. But the population trends highlighted by their findings suggest that grey-headed flying-foxes should be delisted as a threatened species, the authors say.

“There is often reticence about delisting threatened species. There may be concerns that the science underpinning such decisions may be flawed, or inertia and dogma regarding a species’ status or population trajectory might be at play. In this situation the status quo may be difficult to challenge,” they write.

“The data presented here are a good-news story,” they add.

Intensifying heatwaves and other extreme weather conditions necessitate close monitoring of the population, the authors say. Such methods could include mobile bird and bat detection radars and artificial intelligence video interpretation software.

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