Vehicles, natural predators and foxes have been blamed for the death of 70 per cent of eastern quolls reintroduced on the Australian mainland earlier this year.

Twenty of the marsupials were released in Booderee National Park at Jervis Bay on the NSW south coast in March.

Hailed as a landmark re-wilding trial, it was the first time the eastern quoll had returned to the wild on the mainland since they were wiped out more than 50 years ago.

The quolls were fitted with tracking collars so their every movement could be tracked, and the initial results of the pilot has found 14 of the 20 animals have died.

Rewilding Australia director Rob Brewster said the organisation had had no data on what exactly would happen to the spotted marsupials when they were released to the wild.

"We've still got six going, four girls and two boys, but it's been a range of threats that we've identified," he said.

"I guess we can use that information to design a program for next time we trial a reintroduction of eastern quolls.

"Overall, it's a reasonable result for a pilot trial and it provides us with a lot of valuable information on the real threat levels to eastern quolls on mainland Australia."

Four of the remaining eastern quolls in Booderee National Park are females, with the other two males. ( Supplied: WWF )

Two of the unlucky quolls had a run-in with a diamond python — one was discovered in a python's stomach and the other was found dead with a python tooth embedded in it.

"We haven't yet confirmed whether it was a direct result of that python attack, but we always knew that natural predation might play a role in impacting our very small population of eastern quolls," Mr Brewster said.

"We've also had road mortalities. None of our quolls have left the national park. That is a success for us.

"However, four of our quolls took up residence near some fairly busy roads and they were unfortunately hit by cars.

"We always knew it was a potential threat but we didn't think it would be as significant as it has been."

Foxes still a big problem

Some of the quolls fell victim to foxes, despite concerted baiting programs in the national park, and another one was taken by a domestic dog.

Mr Brewster said while it was impossible to completely remove foxes from the area, they were ramping up efforts to control numbers outside the park.

Tasmanian Quoll Conservation Program species coordinator Wade Anthony said any loss of quolls in the project was disappointing.

"It was a nervous time for us. Obviously they're animals that have been bred in captivity at our sanctuary, and a reintroduction like this comes with associated risks," he said.

"To see those sorts of numbers, we're talking 75 per cent over three months. It's probably higher than we expected.

"There will be people that sit on either side of the fence here and say we shouldn't have done it or should have done it."

Hope for baby quolls over coming months

Mr Brewster and Mr Anthony remain confident the remaining quolls will survive and breed over the coming months.

Rob Brewster and Wade Anthony are hoping the remaining quolls will successfully breed. ( ABC News: Barbara Miller )

"We know the boy quolls are very interested in the girl quolls at the moment. They're essentially playing musical sheds," Mr Anthony said.

"They're moving between some built structures in the park that they're sheltering in and they're interacting.

"Hopefully over the next couple of months our tracking program will pick up some very small eastern quoll babies. That will be a very good sign for the project."

The project team will now assess whether the threats can be limited enough to allow for a further round of quoll rewilding.