Seven Tasmanian devil joeys have been born in the wild at Aussie Ark wildlife sanctuary in NSW's Hunter Valley - the first such births on the Australian mainland in 3000 years.
Aussie Ark said this was "a special kind of baby boom".
Aussie Ark, in partnership with Re:wild and WildArk, are celebrating the birth of the joeys born to adults released last year into the 400-hectare wild sanctuary, in Barrington Tops, for the first time ever.
Aussie Ark drew international attention when Hollywood superstar Leonardo DiCaprio pledged $1 million through the US-based organisation Global Wildlife Conservation, following the devastating bushfires in Australia.
DiCaprio is part of the Re:wild project, through his work with the US-based organisation Global Wildlife Conservation.
Tim Faulkner, president of Aussie Ark, said he was "very proud" of the births, which he described as a "very big milestone".
"There is so much at stake here," Mr Faulkner said.
"We have been working tirelessly for the better part of 10 years to return devils to the wild of mainland Australia, with the hope that they would establish a sustainable population.
"If the devils don't breed, it's all over.
"Once they were back in the wild, it was up to them, which was nerve wracking. We had been watching them from afar until it was time to step in and confirm the birth of our first wild joeys. And what a moment it was."
WildArk general manager Kirstin Scholtz said it was "an inspirational achievement by the Aussie Ark team".
"It shows the positive impact we as humans can have on the environment, if we want to," Ms Scholtz said.
"The project, while in its infancy, shows the potential that exists to return our wilderness areas to the thriving, abundant ecosystems they once were. I encourage all Australians to join us on this journey."
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Mr Faulkner said the joeys were the size of "shelled peanuts" when first spotted in their mother's pouch.
"The joeys are born after only a 21-day pregnancy. [At that point] they're the size of a grain of rice. They crawl their way into the pouch. Once they're there, they become fused onto mum's teat," he said.
Aussie Ark released 26 adult Tasmanian devils into its wild sanctuary in late 2020, with seven of those being reproductive females.
Given this, Aussie Ark is estimating the birth of up to 20 joeys in the wild this year.
"Initial pouch checks of the seven confirmed so far, show the joeys are in perfect health and developing as they should be," Mr Faulkner said.
Aussie Ark rangers will continue to monitor the mother devils through camera traps and will conduct follow-up pouch checks in the coming weeks to ensure the health and wellbeing of the mother and joeys.
Tasmanian devils vanished entirely from mainland Australia in large part because they were out-competed by introduced dingoes, which hunt in packs.
Dingoes never made it to Tasmania, but a transmissible, painful and fatal disease called devil facial tumour disease (DFTD) did.
It's the only known contagious cancer. It decimated up to 90 percent of the wild population of Tasmanian devils. Just 25,000 devils are left in the wild of Tasmania.
"Having a population of Tasmanian devils away from the diseased landscape in Tasmanian is crucial," Mr Faulkner said.
"By having devils back in the environment, they help regulate feral introduced pests like the fox and cat."
As such, the devils help other native animals to survive and thrive.
"The ultimate success is a self-regulating, self-sustaining population of devils on mainland Australia balancing the greater ecology," he said.
"But this is in its infancy."
Scientific work will be needed to "know that it works".
Mr Faulkner said Aussie Ark's plans were to "rewild Australia".
"The devil is leading us on that journey."
For the last decade, the Aussie Ark team has been building an insurance population of Tasmanian devils and learning everything they can about the animals, including about their reproductive physiology, behaviour and ecological needs, leading to the reintroduction of 26 adult devils last year.
"The fact that the adults have adapted so quickly is remarkable and the joeys are one of the most tangible signs that the reintroduction of Tasmanian devils is working," said Don Church, president of Re:wild.
"This doesn't just bode well for this endangered species, but also for the many other endangered species that can be saved if we rewild Australia, the country with the world's worst mammal extinction rate.
"Tasmanian devils are ecosystem engineers that can restore and rebalance the wild to the benefit of other native wildlife, the climate and people."
As native apex predators and the world's largest carnivorous marsupials, Tasmanian devils help control feral cats and foxes that threaten other endangered and endemic species.
Because they are scavengers, they help keep their home clean and free of disease.
Aussie Ark selected the 26 devils for reintroduction based on those most suitable to breed with one another without any inbreeding.
The wild sanctuary prevents the spread of disease, feral pests, noxious weeds and fire, which was catastrophic last year for many parts of the country. The wild sanctuary also keeps cars out, ensuring that the devils learn not to associate cars with food - an association that could be deadly when they are more widely released.
Aussie Ark's Tasmanian devil breeding program is the most successful conservation breeding facility for the endangered species on mainland Australia.
Aussie Ark founded a Tasmanian devil breeding program in 2011 with 44 individuals. Today, it's home to more than 200 devils, which is about 50 percent of the entire captive insurance population spread across mainland Australia.
Over the years, more than 390 devils have been born [in captivity] and raised at Aussie Ark in a way that encourages and fosters their natural behaviours, helping ensure that they maintain all the skills they need to survive in the wild.
In the next two years, Aussie Ark will do two additional releases of 20 devils each. The animals will be monitored through regular surveys, radio collars fit with transmitters and camera traps.
This will give the researchers the opportunity to learn about how the devils are faring, where they are claiming territory, what challenges they are facing, what they are eating and whether they're reproducing.
In one recent discovery, Aussie Ark rangers witnessed two Tasmanian devil sisters who had been apart for two years come back together again in the wild. All of this information will help to inform future releases, including in Tasmania and elsewhere on the mainland, to continually refine the process.
"We've been amazed by the dedicated work of Aussie Ark to repopulate Australia's wildlife. This breeding milestone with the Tasmanian devil program on the mainland represents such a positive step towards seeing our endangered marsupials flourish," said Mark Hutchinson, co-founder of WildArk.
"Tim Faulkner and the whole team are an inspiration to us at WildArk and we're so fortunate to call them partners."
The Tasmanian devil is one of seven cornerstone species critical to Australia's ecosystem that Aussie Ark plans to reintroduce to the wild sanctuary in the coming years.
These species were chosen to help restore natural balance: Eastern quoll, brush-tail rock wallabies, rufous bettong, long-nosed potoroo, parma wallabies and southern brown bandicoots.