Microbats face extinction due to climate change, vegetation clearance

One of Australia’s tiniest species of bat — weighing about the same as a 50-cent coin — could be extinct in less than 40 years, according to new research.

Population trends show the critically endangered southern bent-wing bat are declining at a rate that would result in the species being wiped out within three generations.

They are one of 60 species of microbats in Australia and weigh about 15 grams.

They are mainly found in just a few maternity caves in western Victoria and the world heritage-listed Naracoorte Caves in south-east SA.

La Trobe University ecologist Emmi van Harten began her research in 2015 to learn more about the their activity and how well they were surviving.

She said it was clear urgent action was needed.

“Using the survival rate information we have, no matter what assumptions we make, it does paint a picture that they are in decline, and particularly during drought periods,” Dr van Harten said.

“Assuming the current threats and everything stay in place, if that does occur, then they’re approaching close to extinction within 36 years.”

Dr van Harten said the first year of the study was conducted during severe drought conditions, which showed the lowest survival rates in the population.

Visitors to Naracoorte’s Blanche Cave can spot some of the local bat population.(ABC South East SA: Bec Whetham)

Plummeting towards extinction

She said several threats were causing the bat population to decline.

“But we think that a few of the major threats are loss of foraging resources – there’s been a lot of clearance of natural vegetation and wetland drainage and a drying climate as well at play that’s limiting foraging resources,” she said.

Dr van Harten said hope remained to save the species.

“I do want to highlight here that although that sounds really bleak, that’s if nothing changes and that we really can change that around,” she said.

“There’s limited things that individuals can do in some ways, there’s a lot happening behind the scenes as well.”

bent wing bat
Researchers say bent-wing bats could be extinct within 40 years.(Supplied: Steve Bourne)

Dr van Harten said a national recovery plan had been formed to look at a lot of the bigger picture and how the trajectory of the southern bent-wing bat could be changed.

She said it was important that people stayed out of the caves where bats were roosting and breeding as they were susceptible to disturbance.

“If you do want to go to some caves, or even see the southern bent-wing bat, Naracoorte Caves is a great place to do that.”

Rebuilding homes

Dr van Harten said it was critical to restore natural vegetation and wetlands.

“There’s lots of great community work, volunteer work happening in that space,” she said.

Inside a cave with people touring
Naracoorte Caves offer visitors a chance to view the bats and their pups in the maternity cave.(ABC South East SA: Selina Green)

She also encouraged people to spread the word about how important bats were to Australia’s ecosystems.

“They do kill bats and have been known to take some southern bent-wing bats.”

Bats tagged for monitoring

Dr van Harten’s study started in 2015 and involved tagging about 3,000 of the bats with microchips.

That allowed the research team to track the bats each time they flew in and out of their cave.

Much of that research centered around the Naracoorte’s “bat cave”, which provides a safe haven for breeding females each year.

Despite their diminutive size, the southern bent-wing bat can fly up to 70 kilometers away from their maternity cave in just a few hours.

“It’s told us all these things that we didn’t know before,” she said.

“And it’s incredibly complex and incredibly exciting.”

A PIT-tag used for bats
Tiny PIT-tags have been inserted under the skin of 1,000 Southern Bent-wing bats at Naracoorte’s Bat Cave over summer.(ABC South East SA: Kate Hill)

Dr van Harten hoped future research would reveal more about the bats’ foraging and prey.

She said whole new movement patterns had been identified within the population.

“So once the young become independent, we thought that they stayed there for quite some time at the maternity cave,” she said.

She said they were detected at other caves before suddenly returning to the maternity cave.

“We think that this fits in with what they call the maternal guidance hypothesis, where it seems like the mums are showing all the babies around the landscape, essentially, so that they know where to go,” she said.

“And that’s just one example – there’s so many more questions, both just from understanding how fascinating and amazing this species is, but also for guiding conservation efforts as well.”


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