The southern bent-wing bat is one of five Australian mammals listed as critically endangered, but La Trobe PhD researcher Emmi Scherlies said the reasons for its dramatic decline were a mystery.

"In the '60s they counted 200,000 bats at Naracoorte – in 2009 it was down to 20,000," she said. 

“There are a number of theories, but ultimately we just don’t know why.” 

That original population figure could have been much higher, Scherlies said, noting that some colonies of cave-dwelling bats in the Americas can reach more than 20 million – making the current numbers all the more concerning.

“When you’re talking about critically endangered species you’re used to hearing of 200 individual animals left and, although in this case we’re still talking about thousands of bats, that rate of decline is just so drastic that if something were to happen – like a big drought – there is a certainly a risk of them going extinct,” she said.

And the southern bent-wing would probably never recover were its population to dip into the hundreds, the Bendigo-based scientist said. 

Though the bats enter a state of torpor in caves throughout south-western Victoria and south-eastern South Australia in winter, in summer they congregate to breed in just two sites: one in Warrnambool and the other in Naracoorte.

“When the bats congregate en masse they lift the temperature at Bat Cave an additional 12 degrees,” Scherlies said. 

“And they need to raise the temperature in these maternity chambers to keep their pups warm, because they’re born without fur.

“So we assume they wouldn’t be able to see their population drop to, say, 200 bats, and still raise the temperature to the level they need to raise their young.” 

But Scherlies is hoping her PhD research can help prevent that assumption from being tested. 

“We don't realise how much good bats do us each and every night,” Scherlies said. 

“The southern bent-wings only eat insects, so every night they eat thousands of mosquitoes and moths and agricultural pests – they're doing us a big favour.

“Without bats, our world would be a really awful place.” 

In January next year and again in 2017 she’ll head to Naracoorte with a team of researchers to inject 2000 bent-wings with the latest in animal-tracking technology: passive integrated transponders, or PIT tags. 

Scherlies’ hopes the microchips will start piecing together the puzzle and – ultimately – solving the mystery of the bats’ rapid decline. 

“We don’t even know so many of the basics: how many males are there and how many females are there in the cave? Is that a problem? Once the young are birthed are they coming back the next year or did they not even make it through there first winter?”

“Winter is a hard time for them, if they didn’t manage to fatten up enough they might not even be making it through that first season – but to all those sort of questions we just don’t have the answers.” 

The latest in animal-tracking technology could solve the mystery of the disappearing southern bent-wing bat – which has frustrated the efforts of scientists for decades. 

“Ironically it’s one of the most studied bats in Australia and yet we know so little about it,” PhD researcher Emmi Scherlies said. 

The problem has been an inability to monitor the same bats over successive years. 

“It’s only been in the last 30 years or so we’ve been able to trap them and really study them,” she said. “That also requires re-trapping bats… and the re-trap rate is really low.”

But the days of attaching bands to bat wings could now be numbered. Scherlies and her team from La Trobe will instead inject the bats with PIT tags – microchips similar to those used in domestic dogs, but far smaller. 

The team will attach antennae around the entrance the one of the two places in the world the bats congregate to breed: Bat Cave in Naracoorte. Though the technology is high-tech, some of the testing was more DIY. La Trobe professor Noel Meyers devised a home-made cannon to test tags.

“We wanted to test our measurements if, say, nine bats went through at same time at different speeds,” he said. “We measured for a slow poke going 10 kilometres per hour… and even got one flying at 160km p/h!”

Ruth Lawrence has been leading expeditions into the Naracoorte Caves National Park for nearly two decades but has never been allowed into the highly-restricted Bat Cave. 

“I’ve been a caver for 35-years and I’ve never been allowed to go in before… until October,” she said. 

The La Trobe senior lecturer entered the world heritage site to help install the antennae which will track the southern bent-wing bats which breed there every summer.

“The entrance to Bat Cave is just a hole in the ground, maybe four metres in diametre,” she said. “There’s a fixed ladder which descends into the cave and once you climb down it just opens up into a chamber maybe 50m across.”

From there, the a tunnel winds its way though the limestone – narrow and some points and wide at others. Its walls are white and floor shades of muddy brown until, you reach the maternity chamber, where the antennae will be installed in January. 

“The floor of that cave is pitch black,” she said. “It’s got to be the darkest cave in Naracoorte.”

The reason: thousands of furless, bent-wing pups cling to the roof while their mothers forage.

“All that guano is… extremely ‘aromatic,’” Lawrence. “Then there’s the buzz of thousands of bats talking to one another.”

Hearing that buzz and smelling that guano was the culmination of years work for Department of Outdoor and Environmental Education lecturer.

“I've been talking students from Bendigo La Trobe to Naracoorte for 17 years looking at a variety of different aspects of the caves, from the groundwater to the stalactites and the stalagmites,” she said.

“We look at the biota in the caves, both the ancient dead – as in the fossil deposits that make it a world heritage site – and the existing fauna.

“The bats are a such an important living component to the cave system… but we’re never allowed in Bat Cave.” 

It was on one of these trips that PhD researcher Emmi Scherlies – then an undergrad – first saw the southern bent-wing. But it wasn’t until last month she held one in her hand.

“They’re so light and so adorable, all soft and furry with cute little eyes,” she said.