Ghost bat autopsy finds cane toad bones, explains population's freefall in NT, Qld: expert

Cane toad bones found in a mummified ghost bat's stomach have been described as the "smoking gun" that explains the mammal's local extinction in Queensland and parts of the Northern Territory.

The discovery could spell doom for Australia's only carnivorous bat, with their last northern strongholds in Arnhem Land and the Kimberley in the path of the feral toad.

It has also shed light on the mysterious rapid decline of small to medium-sized mammals in northern Australia - considered by some to be the result of the complex interaction of changing fire regimes, new kinds of feral grass, and the long-term toll of cats, dogs, toads and other pests.

Scientists have said a wave of extinction was rolling through the tropical north.

Environmental consultant Dr Arthur White has been making expeditions to Kakadu National Park to discover why ghost bats have entirely vanished from the Riversleigh area and the Boodjamulla National Park in Queensland.

"We were really puzzled by this," he said. "We had no clear-cut explanation for why ghost bats should have declined.

"We had circumstantial evidence the decline seemed to happen 15 to 20 years after the arrival of cane toads in an area.

"That implied cane toads were involved in the loss of ghost bats. We went looking for evidence."

That meant foraging for cane toad bones in the dung on cave floors. No-one had yet been able to prove ghost bats ate cane toads.

On his most recent trip, in the depths of a remote cave, he found the object of his quest.

"At one site we found a whole lot of dead ghost bats on the floor of the cave," he said.

"We collected them and brought them back and autopsied them. One of the bats had the remains of a young cane toad still in its stomach.

"It was very easy to identify what that meal was. It was the first proof we had of ghost bats actively preying on cane toads - and paying for it with their life."

Cane toad toll takes 20 years to register

There are now an estimated 10,000 ghost bats in the wild, with the figure declining by 10 per cent every 24 years, according to Dr Damien Milne, a senior scientist with the NT Government's Department of Land Resource Management.

"In recent times there have been significant declines in Queensland," he said. "In the Pilbara area they expect all the ghost bat sites will be potentially mined in the next 30 years.

"In the dry season they form maternity colonies. There are only a handful of maternal colonies across whole of Australia. If that gets stuffed up then its bad news for the entire population.

"The Top End and the Kimberley seems to be OK. The largest known colony in Australia is at Pine Creek.

"A count done a few years ago recorded 1,500 individuals. The last count was 564."

But Dr White said ghost bat populations had suddenly slumped 15 to 20 years after the arrival of cane toads in Riversleigh, and he suspected a sudden a similar decline was underway at Kakadu.

"Ghost bats are locally extinct in the Riversleigh-Boodjamulla area," he said.

"Cane toads first came into the area in 1986. It took 15 to 20 years before we really noticed something was seriously wrong with the populations.

"In the case of Kakadu cane toads didn't reach that part of the world until 1995. We're really starting to see populations fall away.

"We've investigated all of the largest known colonies in the Kakadu National Park. Of those only one appears to be viable - the others either have no ghost bats in them at all or are down to their last one or two."

Carnivorous ghost bats the 'fighter jets' among flyers

The ghost bat - Australia's only carnivorous bat - is "the F/A-18 of the animal world", according to Darwin naturalist Ian Morris.

They deploy fine-flying skills and sharp eyesight to snap birds, insects and other bats on the wing. They are also known to drop from trees on unsuspecting prey.

"They are a very complex highly evolved animal," Mr Morris said.

"Once they capture something they return to a large rock or a flat, hard area and they'll eat the food there. They dismember and eat the bits they want. They leave behind wings and feathers.

"You can keep coming back morning after morning and see what they've been eating.

"One ghost bat one time out at Oenpelli was using the wing of a Cessna in a hanger as its feeding table. The poor guy that owned the Cessna thought someone was sabotaging him every day.

"There was blood running down the side of the plane. All sorts of mess on the wing.

"He thought someone was having a joke at his expense until I pointed out that's what ghost bats do. Your plane has been selected and you should feel pretty honoured.

"They've got no hands. They've got a huge set of choppers. They have to basically dismember and eat whatever it is they've caught with their mouth.

"It can be messy."

Ghost bat once common throughout Australia

At the beginning of the 20th century the ghost bat ranged through eastern and central Australia and as far south as the Flinders Ranges.

Furtive and nocturnal, few noticed when the bat was gone.

"Entire colonies of ghost bats died in their caves," Mr Morris said.

"There are no ghost bats in South Australia. They went from a common animal to extinct in a short space of time. They were in eastern Australia as well. Queensland had good colonies until recently.

"We're next in that process with toads settling around us now.

"Arnhem Land and the Kimberley had big populations of ghost bats. The Kimberley still does. How long we can maintain that I don't know."