The kōkako population in the Pirongia Forest Park in Waikato is expected to reach about 60 this year after the native bird had disappeared from the maunga in the 1990s.
A joint project between the Department of Conservation and the Pirongia Te Aroaro O Kahu Restoration Society (PRS) has worked to bring back the kōkako.
About 40 were released in the park in 2017 and 2018 to kickstart a breeding programme.
Clare St Pierre from the society said with the latest nesting season over it is hoped another 20 chicks will be raised successfully.
''It was in the 1990s the last were captured to stop them going extinct, so DOC arranged that. I think there were five caught and they were transferred to a captive breeding programme and luckily some of them bred and so their progeny was still available to us to bring some back.''
St Pierre was involved in the founding of the society at a time when there were no kōkako at all in the park.
''At the first meeting to start up the society, people came who said we remember hearing the kōkako back in the 1980s and they wanted to hear it again and that was one of the founding aspirations.''
She said the birds were in decline due to predators, such as rats, stoats, possums, feral cats and hedgehogs which all took their toll.
''The eradication target is to keep them under 2 percent index.''
The main work of the society is to look after bait stations on the maunga.
Volunteers also set traps around the base of the nesting tree.
"We set 20 rat traps and one to two possum traps and check them every four days. We reset and re-bait, as necessary. Rats and possums have been caught, so it is necessary," she said.
Once a nest has been identified, a schedule is drawn up and every four days a volunteer checks on a nest for an hour, recording the birds' behaviour.
DOC biodiversity ranger Cara Hansen works closely with the PRS providing technical advice and support.
"The PRS is doing fantastic work on the maunga, including 1300 hectares of annual pest control, which DOC supplements with landscape-scale pest control across the entire 12,500 hectares of forest. It's making a difference, and the birds are evidence of that.
''Fledging day is long anticipated by all. It's when a young bird, encouraged by its parents, wanders off the nest and takes its first daring leap off the branch. When it makes the leap, there is a sense of personal accomplishment.''
But not all birds are lucky in love.
"In Pureora Forest Park a majestic male kōkako was caught for translocation to Pirongia in 2018. He weighed 283g (a small adult is 190g) so he's really big," St Pierre said.
''The big male bird, aptly named Pavarotti, [after the late Italian opera singer] has been seen with three females and has attempted a duet with two. Unfortunately, Pavarotti hasn't yet found 'the one'. We're hoping he finds true love next season."