Four of the bettongs were killed by foxes and one by a bird of prey with six other deaths under investigation. Another bettong may still be alive with a faulty collar and all six surviving females have pouch young.

Eastern bettongs have survived only in fox-free Tasmania for about 100 years. Sixty bettongs were transferred to predator-proof areas of Canberra in 2012 with the population since growing to about 275.

The trial reintroduction of the species in the Lower Cotter Catchment represents the next phase of mainland reintroduction of what is sometimes called the rat kangaroo.

A review of the outcomes of the trial, expected mid-February, will be used to determine whether bettongs could survive in the wild.

"Due to the unknowns surrounding this project - because it's never been attempted before with a species on the mainland in this kind of environment - the lowest risk is to release a few animals, monitor them really carefully, gain as much information as possible so then it allows you to make an informed decision about a bigger project in the future and whether it's feasible or not," research lead Will Batson said.

"What we have proven is that bettongs aren't necessarily a big beacon in the landscape sucking all the foxes in, so in that way I'd say it's been massively encouraging, and currently although it's not definitive until the review, I think we've shown that there's a possibility that we could get viable populations of this species established with foxes and cats in the wild environment."

ACT Parks and Conservation director Daniel Iglesias said the trial reintroduction was imperative in saving the eastern bettong from extinction. But he said even if the trial proved successful there were no guarantees a population would be established in the ACT.

"To those that think 'oh, gee, you're exposing these animals and some of them may die', I would say the big picture is what we're looking at," he said.

"If we're going to seriously look in this country at reversing decline in our native animals we need to be supporting innovative projects like this one that have a go."

An intensive fox and dog management program spanning 8000 hectares has been underway since mid-2015 to allow for the project.

Only when pre-determined reductions in levels of fox activity were met were the bettongs released. It is unknown how much the fox management program cost.

"The other important thing to note is that by reducing the foxes we're also delivering a benefit to other animals that are susceptible to animals," Mr Iglesias said.

"Foxes will take lizards, they take birds, and by controlling foxes in this way we're reducing the pressure on those animals as well, so there's actually a much bigger benefit to controlling the foxes than just protecting the bettongs."

Threatened Species Commissioner Gregory Andrews paid tribute to the work of the Australian National University, the ACT government, Mulligan's Flat and the Woodlands and Wetlands Trust for their role in the program.

The Lower Cotter Catchment eastern bettong project forms part of the Australian Government's National Environmental Science Programme.