Deep in caves across south-east South Australia and western Victoria, thousands of southern bent-wing bats are sleeping their way through the long, cold winter months.
Hidden under the skin of a number of these tiny bats is a microchip, allowing a La Trobe University researcher to follow their movements and hopefully shed some light on why the secretive species is in decline.
The bats, known as Miniopterus schreibersii bassanii, are one of just five Australian mammals listed as critically endangered and a national recovery plan has been developed to help the species survive and flourish in the wild.
Naracoorte's aptly named Bat Cave is one of the two key maternity sites for the species and it is here where PhD student Emmi Scherlies is hoping to learn more, with the help of some state-of-the-art tracking equipment.
Holding a PIT — or Passive Integrated Transponder — tag, Ms Scherlies shows the tiny size, necessary for it to be inserted into an equally tiny bat.
"Southern bent-wing bats are only 15 grams, the equivalent of a 50 cent coin," she said.
"The body is the size of your thumb."
The tag acts as a kind of barcode for an individual animal, with an antenna in the cave recording the comings and goings of the tagged bats, giving Ms Scherlies an insight into their movements.
"Bats are very good at keeping their secrets," she said.
"By tagging the bats, we are able to track them over time and see what happens. We can follow the bat's movements and survival over time."
PHOTO: 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)
Catch and release
Over three weekends last summer, Ms Scherlies and 25 other volunteers worked through the night to catch and tag 1,000 bats, often emerging from the dark of the cave when the sun was just beginning to rise.
One of the most common questions Ms Scherlies gets asked is, "How do you catch a bat"?
She explains it takes time, patience and a lot of willing volunteers.
Using a bank of harp traps, which are a large metal frame with two layers of strings stretched across, volunteers wait until the bats fly in and flutter down between the strings to a waiting catching bag below.
But the method can be a little hit or miss for the wily micro bats.
"Theoretically, it works," she laughed.
"They are very good fliers and a large proportion will just navigate through both banks of strings and just keep flying."
Once caught, the tiny PIT tag was inserted under the skin and the bats were released.
The volunteers had a very narrow window to target the young bats, which are important to the study.
"January is when the young bats start becoming independent and start flying by themselves, so we wanted to tag a significant amount of those young bats because we knew how old they were," she said.
Answering the big questions
Over the length of the study, Ms Scherlies is hoping to answer some of the bigger questions facing the species.
Are young bats at higher risk of dying during their first year? Do females have a higher mortality rate than males?
"There is a lot of things that we don't know," Ms Scherlies said.
"But ultimately it would be nice to be able to shed some light on questions like why they are in decline and why their population isn't growing."
The population of southern bent-wing bats has been steadily declining in the last 40 or 50 years and no-one is sure why.
Back in the early 1960s, their numbers at Naracoorte were estimated to be as high as 200,000, with the lowest count in 2009 at around 20,000.
"There is still a lot of questions about why exactly that is. Certainly there were episodes where significant drop-offs happened during drought but we don't know why their population isn't growing again," she said.
Data is already piling in for Ms Scherlies to wade through.
"There is in excess of 200,000 detections at the moment," she said.
PHOTO: La Trobe University PhD student Emmi Scherlies is studying the Southern Bent-wing bat population at Naracoorte Caves. (ABC South East SA: Kate Hill )
Study to expand
Next summer, Ms Scherlies and her team of volunteers will return to Bat Cave to tag 1,000 more animals.
There are already plans to use a second antenna at additional cave sites next year to build a bigger picture of the tagged bats movements at different sites and over different seasons.
The study will run until 2018.
The tiny species of micro bat has captured her imagination, Ms Scherlies confesses and her interest has even earned her the nickname "Batgirl" among her colleagues.
"I just think they are absolutely magical, amazing. They are placental mammals, just like us and incredibly intelligent," she said.
"There is information that we need to know and hopefully we help find something out and help conserve this species for the future."