As Mulligans Flat Woodland Sanctuary arm-up to cull rabbits for native species' protection, predator reintroduction is having the opposite effect, seeing animals eaten to avoid overpopulation.
Staff have identified the fur of vulnerable eastern bettongs in the scats of eastern quolls since their reintroduction to the sanctuary's northern enclosure in 2016.
But, while quolls are known to prey on small mammals, it was impossible to know whether they had been killed and eaten, or scavenged already dead, an ACT government spokeswoman said.
The predation was helping to maintain the health of prey populations in Mulligans Flat and the ecosystem more broadly, but a plan to shoot and kill all rabbits in the sanctuary could prove counter-intuitive and wildly expensive, pest control expert Dr Mike Braysher says.
This would be especially true if Mulligans Flat was considering more wild release programs, such as the one in the Lower Cotter that left 67 eastern bettongs dead.
Former Mulligans Flat manager Dr Will Batson had previously not ruled them out, saying animals would be considered on a "case-by-case basis".
The ACT Scientific Committee indicated it would advise the government against further wild releases of bettongs, saying it would not be sensible until some new fox control technology came about.
"Why spend all this cost on eradication when [rabbits would] have to exist with these other animals in the wild anyway, if that's the way they're going? It just doesn't make sense," Dr Braysher said.
"I would contend, although maybe they'd protest, that they should have an area with quolls, bettongs and a few rabbits and see where they can survive."
The number of rabbits in Mulligans Flat's northern enclosure and the resulting culling cost was still being determined but three had been detected on March 27, the government spokeswoman said.
One female rabbit was able to give birth to 50 kits a year and an unchecked rabbit population would compete with native species for food and disturb the groundcover.
An eradication program in the same enclosure in 2016 was funded under ACT Parks and Conservation's operational budget and an additional $125,000 was contributed by the territory government.
Dr Braysher said it would be almost impossible to know if all rabbits had been eradicated because the last remaining ones usually became "so scared and skittish, they learned to avoid things".
It would be impossible to eradicate entire populations of rabbits and foxes in the wild, he said.
Mulligans Flat's northern enclosure alone has 20 gates around its exterior, most of which are left unlocked during sanctuary opening hours. They had been designed to close automatically after being opened and staff had been educating Canberrans about the importance of shutting them, the government spokeswoman said.
"The predator proof fence is specifically designed to exclude rabbits," she said.
Dr Braysher said Mulligans Flat should be clear with the public about its purpose; whether it would raise predator-wary animals to eventually be released into the wild, or forever act as a display enclosure for native species.
"It's not going to stop at bettongs. There's no clear plan and no real thought about, 'Is this really realistic? Where's it going to go and where's it going to end?'," he said.
"It's all ad hoc and that's fine to some extent, but the amount of money, staff and resources involved is huge and has the potential to be ... even more.
"It's like Nero fiddling while Rome burns."
Dr Batson initially said the sanctuary would be closed from 6pm to 6am, Monday to Thursday until October as rangers hunt rabbits. The government spokeswoman said the length of the program was still being determined.
A release in the sanctuary's southern enclosure was scheduled for later this year. Having just been expanded, it was the subject of another eradication project.