Chris Jolly keeps track of the quolls through radio signal-emitting collars the creatures wear. (ABC News: Mitch Woolnough)
Conservationists who successfully evacuated a threatened quoll population to an uninhabited island have discovered the creatures may have lost their genetic instinct to avoid predators.
With the species in rapid decline, an insurance population of northern quolls was sent to colonise Astell Island off the coast of north-east Arnhem Land.
It was 2003, and the endangered marsupials were already in trouble by the time toxic cane toads arrived in the Northern Territory.
Although no quolls previously lived on Astell Island, its remoteness meant it was deemed to have a low likelihood of cane toad invasion.
Forty-five quolls were sent there.
“They absolutely boomed in number from 45 to thousands in just a few years, so it was just a great success,” evolutionary biologist and PhD student Chris Jolly said.
Quoll numbers on the island reportedly rose to about 8,000.
Two steps forward, one step back
Researchers, meanwhile, had discovered quolls could be trained not to eat cane toads by feeding them small cane toads laced with a nausea-inducing chemical.
“It’s basically the same process that we go through if we drink vodka heavily one night and throw up repeatedly; the next day we smell vodka and we turn our heads,” Mr Jolly said.
“Animals have to be a lot more cautious, so if something makes them sick they’ll almost never touch it again.”
Chris Jolly has spent many hours tracking quolls, both living and dead, through Kakadu National Park. (ABC Radio Darwin: Jesse Thompson)
To prove the training would work among the Astell Island quolls, Mr Jolly and his colleagues devised a plan to release two groups — one trained, one untrained, but both collared with radio transmitters — into Kakadu National Park.
The plan drew input from academics at the University of Melbourne and the University of Technology Sydney, funding from the Australian Research Council and support from the NT Government.
It was going well until researchers unearthed another evolutionary weakness.
“The ones that weren’t trained, they quickly found toads and ate them and died unfortunately,” said Mr Jolly, who spent long periods of time tracking radio signals through the park’s harsh savanna woodland.
“But the ones that we did train survived for a bit longer.
“Unfortunately, they came to a sad demise at the teeth of our native predator, the dingo, which was a bit of a surprise to us all.”
A similar experiment revealed that Astell Island quolls, unlike those from Queensland, failed to avoid food laced with the scent of their predators.
This led researchers to the realisation that the strong evolutionary pressure that prompted quolls to avoid cane toads and dingoes had disappeared on the paradisiacal island.
The signal sent from radio collars slows once the quolls die, alerting researchers to their fate. (Supplied: Chris Jolly)
Return to the mainland
While the researchers have succeeded in saving the quolls as a stopgap measure, they now face the problem of reintegrating the cohort into the wild.
Although only 13 generations of quolls had lived on the island, Mr Jolly was taken aback by the “very, very rapid” loss of their instincts.
“It seems obvious in hindsight that if you remove animals from their predators, over time they will lose the ability to deal with them,” he said.
One option now is to gradually put the Astell Island quolls back in contact with their predators.
Introducing de-sexed dingoes to the island would cause natural selection on the population and reintroduce a natural fear of their predators, while ensuring the dingo population remained stable.
“If we want to go further and reintroduce them back into the native areas they came from, which is the ultimate goal of all threatened species management, we need to ensure that they can go back into the wild,” Mr Jolly said.
“While we’re isolating them from these threats, it’s possible that we’re sending them down an evolutionary trajectory that just makes them incompatible with release into larger Australia.”