Cave divers search for rare ghost bats after flooding

Deep in Queensland's outback, flat, scorched country plunges into a maze of caves marked only by a few limestone boulders.

For Indjalandji-Dhidhanu traditional owner Ian Saltmere, Camooweal's cave network, about two hours north of Mount Isa, is more than a geological phenomenon.

"In our dream time, there's what we call a rough-tailed goanna and that's where he goes and digs his hole and that [cave is] where he came out of," Mr Saltmere said.

But in 2023, flooding swept through the region, inundating the labyrinth of underground caves.

"I'd seen the caves just filling up one after another and then … it started circling," Mr Saltmere said. "It was like a whirlpool."

As the floodwater receded, attention turned to a rare colony of endangered ghost bats feared to have been wiped out.

A new research project, co-ordinated by the Department of Environment, Tourism, Science and Innovation in collaboration with traditional owners and cave divers, is working to understand whether the bats have survived and how the isolated population can be protected.

Queensland Parks and Wildlife Service senior conservation officer John Augusteyn said finding answers was critical to the species' survival.

"Ghost bats are listed as endangered … they've declined across their range and in numbers," Mr Augusteyn said.

A bat-eating bat

With an upturned nose and white fur, Australia's largest carnivorous bat is unmistakeable.

Mr Augusteyn said the mammal was found right across northern and central Australia and it fed on prey including snakes, birds and other bats.

"They can actually catch them on the wing when they're flying through but, often, they're almost like owls, where they will sit in a favourite perch listening for their prey below," he said.

"They can hear both low and high frequency calls, which means they can listen for their prey and also detect it using echolocation."

But in recent years, cane toads, mining development and cave disturbances have left many of their former roosting sites empty.

The search for scat

Ghost bats are notoriously difficult to find, so researchers have turned to the bats' droppings for clues about the colony's survival.

Grant Pearce is the lead cave diver responsible for collecting the precious samples.

"They're a particular size and a particular shape and even a particular odour. We don't taste them though," he said.

Using environmental DNA (eDNA) droppings and collected prey samples, researchers have started analysing how many bats are thought to exist in the colony, what they are eating and even if they are pregnant.

But working in caves in a landscape where temperatures regularly reach 40 degrees Celsius is no easy feat.

"We have to abseil down into them, and we pop down into large galleries big enough to fit several houses in," Mr Pearce said.

"It's pretty hot work down there … you can sweat buckets of water on each trip without any problem at all.

"But it's worth it when you actually find what you're looking for."

Bittersweet findings

While the full results are not expected until later next year, preliminary testing has confirmed the endangered bats survived the flooding.

Mr Augusteyn said small pockets of air deep within the cave network may have allowed the bats to survive until the floodwater receded.

But further examination revealed population numbers were dwindling and the colony was genetically isolated.

"Sadly, it's a very low genetic diversity," he said.

"If they go extinct, there's no chance of recolonisation."

As the wet season approaches, researchers and divers will have to return in the new year to finish the final stages of fieldwork.

Key questions about where and when the bats breed remain unanswered, but Mr Saltmere is determined to uncover the species' secrets.

"We've got to look after them … it's something to fight for," he said.