A small colony of the native mouse, distinguished from the non-native house mouse by its bigger ears, currently exists at the Australian National University and inside Mulligans Flat.

According to documents tabled in the ACT Legislative Assembly, conservationists aim to breed a "long-term insurance colony" at Tidbinbilla, ultimately releasing them to re-establish a wild population in the capital.

Tidbinbilla senior wildlife officer Jennifer Pierson said the goal was to create a self-sustaining population that was big enough last through the "bust" of Australia's boom and bust cycles.

"Often times that means populations in different places as well, so if one does temporarily blink out that's a fair natural process sometimes but you do need to have that other population," Ms Pierson said.

But while she said it was important to have a goal "to get animals beyond the fences", they had no concrete plans to reintroduce more native animals in the wild.

Previous reintroduction plans by the ACT government for the eastern bettong came under fire when it was revealed all 67 bettongs released between 2015 and 2017 died, with the last eaten by a fox in March last year.

"It did provide an opportunity for us to learn a little more," Ms Pierson said.

The eastern bettong is extinct on the Australian mainland mainly due to predation by introduced feral animals like foxes or cats.

Ms Pierson said the population of New Holland mice at Mulligans Flat helped researchers understand the role it played in native ecosystems

While the hapless critter was food for larger, native mammals like owls, it also helped disbursed seeds through its droppings.

"There's a pretty incomplete knowledge of the full role that they play," Ms Pierson said.

"We might not have a full understanding of what animals do for an ecosystem until the ecosystem's not functioning anymore."

Australian National University ecologist Professor Adrian Manning said the project had huge national significance.

The university's environmental school, the Fenner School, keeps a colony of the mice.

"As far as we know this is the only captive population of this threatened species in Australia," Professor Manning said.

"It emphasises how important the ACT's role is in national species conservation."

Professor Manning said the mouse had been able to persist in some spaces along the coast but inland it had struggled.

"A key factor involved is ... as elsewhere in Australia ... foxes and cats," Professor Manning said.

"Changed fire regimes as well may have affected their population.

"There's quite a bit of concern about their status in the wild."

The Bramble Cay melomys, a rat native to the island of the same name in Torres Strait, was declared extinct by the federal government in February.

It was said to be the first mammalian extinction caused by human-induced climate change in the world.

Australia has the worst mammalian extinction rate in the world.