It was touted as a remarkable success, but, in just under two years, an ambitious reintroduction program has resulted in the death of all wild eastern bettongs on mainland Australia.

Key points: Of the 67 eastern bettongs introduced to the wild 18 months ago, none remain

Of the 67 eastern bettongs introduced to the wild 18 months ago, none remain During the trial release, some joeys were born to the population, the first in 100 years

During the trial release, some joeys were born to the population, the first in 100 years Conservationists say the trial shows fox numbers need to be further lowered

In April 2017, the first eastern bettongs to be born in the wild in 100 years were found wriggling in their mother's pouch.

Eight months earlier, the bettongs who bred those joeys had been released into a restricted area of the lower Cotter River catchment, 20 kilometres southwest of Canberra.

All 67 eastern bettongs and their young have now perished, mostly as a result of foxes.

But the team behind the program said the outcome, though depressing, had given them a new "feather in the cap of their learning".

ACT Parks and Conservation director Daniel Iglesias said the trial had proven that eastern bettongs could, at least for a period of months, reproduce in a wild habitat shared with predators.

Sad, but that's science for you: researchers

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Until the unprecedented wild breeding trial, the species had not existed in the wild of mainland Australia since the 1920s.

The only place in Australia they remain secure is in Tasmania, due to the absence of their main predator, the fox.

In the ACT there are two protected populations: just over 100 living at Mulligans Flat Woodland Sanctuary and a breeding population at Tidbinbilla Nature Reserve.

Both groups flourish behind a fence that protects them from foxes.

When the wild breeding trial began, scientists were cautiously hopeful, but well aware of the risks.

"It's not ideal to lose animals. This is the wild, and we are in an environment where we can only supress fox and cats, we can't get rid of them," ecologist Will Batson said in 2017.

Feral pest baiting, the team acknowledged, was arduous work.

At one stage they were servicing 150 bait stations each week, while using between 30 and 40 wildlife cameras to monitor what animals were in the area.

The program reduced fox numbers "significantly", enough to make history with those first bettong joeys.

Australia's 'appalling' conservation record

In 2017, scientists discovered joeys in the pouches of wild bettongs for the first time in a century. ( ABC News: Craig Allen )

Associate Professor of Wildlife at Deakin University Ecology Euan Ritchie said the results were tragic.

"Obviously we have an appalling conservation record in Australia," he said.

"Over 30 species have become extinct since European arrival and we really need to be doing everything we can to encourage recovery of a mammal population.

"That's really challenging and we have to take calculated risks sometimes."

ACT Chief Minister Andrew Barr holds a bettong, while announcing an eco-tourism strategy during the territory election. ( ABC News: Ian Cutmore )

Associate Professor Ritchie more funding for conservation was essential in the struggle to return extinct wildlife to their native habitats.

"Australia spends much less than one per cent of it's total budget on environmental protection and conservation of its native plants and animals, which is much less than other countries around the world," he said.

"So we need an immediate increase to be at least two per cent of GDP.

"We simply can't afford not to."

Associate Professor Ritchie said a number of factors could have led to the trial's poor outcome, including insufficient ground cover — to help the bettongs hide from predators — or higher numbers of other prey that could have attracted the foxes.

"I think the thing that we also need to focus on is that, in this case, although foxes have taken the bettongs, there are instances of similar species surviving in the wild as well in the presence of cats and foxes," he said.

Despite bloodshed, trial gives hope for small mammals

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Mr Iglesias said the next step was to analyse the trial's findings to determine how best to turn that early success into a long-term strategy.

"One of the greatest questions for conservation in Australia is how can we reintroduce animals into an environment where there's predators like foxes," he said.

"If we could solve that problem, it would mean we could reverse one of the worst records in the world for the loss of mammals from a single continent."

He said the trial had given them some "tantalising bits of information" that could provide a solution.

"In the end all 67 of those bettongs were taken by foxes but what we learned in the process is that we can have the bettongs with the foxes," he said.

"But what we now need to focus on is how can we maintain that population of foxes low enough so that the bettongs can survive and reproduce ongoing forever.

"That's the key big challenge we have now."