Lord Howe Island's entire population of endangered woodhens has been released back into the wild after a successful captive management program.

Key points: Endangered Lord Howe Island woodhens have been released back into the wild

Endangered Lord Howe Island woodhens have been released back into the wild They were moved into captivity, along with Lord Howe currawongs, for their safety during a rodent eradication program on the island

They were moved into captivity, along with Lord Howe currawongs, for their safety during a rodent eradication program on the island The woodhens and currawongs are thriving and have already resumed breeding

The birds were taken into captivity to keep them safe during a large-scale rodent eradication program on the world-heritage-listed island, 600 kilometres off the Mid North Coast of New South Wales.

The program was introduced on the popular tourist island last year because the rodents had reached huge numbers and were killing native birds and wildlife and ravaging crops and gardens.

The Member for Port Macquarie, Leslie Williams, said the rodent eradication project was the largest ever attempted on an inhabited island.

"This is the largest single conservation action in the state's history," she said.

The Lord Howe Island woodhen is found only on the island, and each individual is monitored. ( ABC RN: Ann Jones )

"It was made possible thanks to a partnership between the Lord Howe Island Board and Department of Planning Industry and Environment."

Relief and sacrifice for project supervisor

Lord Howe Island rangers and Sydney Taronga Zoo staff were involved in the program. ( Supplied: Lord Howe Island Board )

The woodhens and many of Lord Howe Island's currawongs, a threatened sub-species of the mainland pied currawong, were captured and placed in captivity before the rodent eradication began mid-way through 2019.

Around 230 woodhens were held in specially designed enclosures on the island during the program with Taronga Zoo playing a vital role.

The Taronga Zoo Lord Howe Island Captive Management Project supervisor, Michael Shiels, said years of planning, including a trial run, went into the project.

"We had to sit down and work out what to feed them and how to look after them, and how many staff we would need and what kind of facility we would need to construct," he said.

"The enclosures had to be mouse-proof and rat-proof and safe for the birds."

Mr Shiels, who spent around 10 months on Lord Howe Island during the project, said there was a great sense of accomplishment when the birds were released.

"It is a great deal of pressure having almost every animal of a single species in the palm of your hand," he said.

"So to have them out and know we've done a good job is an amazing relief, there's a great sense of achievement and it's exciting.

"I just got home, it was a big commitment, and also a big commitment from my wife and three kids, as I was on Lord Howe for pretty much the whole time."

Helicopters used in 'extremely inaccessible territory'

All the Lord Howe currawongs have also been released back onto the island, after the baiting program. ( ABC News: Mridula Amin )

Mr Shiels said an important part of the program was working out how to capture and release the birds.

The remote nature of some of the mountain-top territories meant helicopters had to be used during both the capture and release process.

"We designed a crate that could fly underneath the helicopter with the birds in them, so each bird was in an individual crate within that," he said.

"There were three layers, so we called it a 'woodhen hotel', and it was clipped under the helicopter using a large cable."

The Chair of the Lord Howe Island Board, Peter Adams, said the woodhens and currawongs were released in stages.

They started with the Lord Howe Island currawongs late last year, then the mountain populations of woodhens, and finally, in recent weeks, the lowland woodhens.

"The helicopters were used to take the first woodhens back to Mt Gower and Mt Lidgbird," Mr Adams said.

"It's extremely high and inaccessible territory, so it was really the only way to take them back safely and release them where they were caught."

The view from Mt Gower on Lord Howe Island shows just how difficult it is to access all terrain. ( Supplied: Jack Shick Photography )

Birds back breeding 'within minutes'

Mr Adams said the woodhens and currawongs had both settled back in well and were already breeding.

"The woodhens in the mountains were released earlier," he said.

"The scientists who released them reported that within minutes their mating activity had commenced, so that was an interesting side-story — they wasted no time.

The endangered Lord Howe Island woodhen will be monitored after the pest eradication. ( ABC News: Mridula Amin )

"The breeding period is spring and summer, they can breed several times a year, and we already have two confirmed chicks that have been born and are successfully running around from some of the first few woodhens that were released.

"The currawongs were released in October and they have already successfully had chicks and settled back into their different territories."

Residents on Lord Howe Island are glad to have some of their feathered friends back home.

"The people on the island have missed the Lord Howe Island woodhens that were off in the captive management program," Mr Adams said.

"They will wander around your yard, they will announce themselves, the residents of the island love them very much.

"We have already had happy stories about them returning to various yards and areas around the island, they are very friendly and quite bold.

"Traditionally they haven't really had predators."

Rodent traps were used on Lord Howe Island during the large-scale pest eradication. ( ABC News: Mridula Amin )

Rodent eradication on track for success

Lord Howe Island will now be monitored for two years, with strict biosecurity measures enforced to prevent rodent incursions.

Researcher Melanie Massaro checking a Lord Howe currawong. ( Supplied: Melanie Massaro )

"If no rats or mice are spotted over the next two years we will be able to declare Lord Howe Island a rodent-free zone," Mr Adams said.

"We will be monitoring and ensuring the program has been successful, looking at biodiversity and all sorts of things."

Researchers are also specifically studying the impact of the rodent removal on the Lord Howe currawong.

Melanie Massaro from Charles Sturt University said she hoped the study would provide a broader understanding of the impact on the overall ecosystem.

"An ecosystem is really the interaction of various species, so if you then take out a huge biomass, which the rodent eradication is doing, obviously that will change the entire ecosystem," Dr Massaro said.