Taranaki's kōkako population is slowing climbing, with four more of the endangered birds making the region home over the past week.

Released into the Parininihi Forest, near Urenui, the new residents are a part of a catch and release operation in which 20 kōkako will be taken from the Rangitoto Ranges, on the northern edge of Pureora Forest Park, King Country, and relocated to the area this month.

Leading the efforts, Tiaki te Mauri o Parininihi Trust, responsible for bringing the rare bird back to rural Taranaki after a near 20-year absence, hopes to one day have 500 kōkako living at Parininihi.

And according to trust chair Davis McClutchie, they are well on their way.

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Eighteen years after the last kokako, named Tamanui, was moved from Parininihi to a captive breeding programme run by the Department of Conservation (DOC), 12 of his descendants were brought to the national forest in May last year.

Davis said the additional 20 kōkako marked an important milestone for the Ngāti Tama-led trust and are critical in building a genetically healthy and robust kōkako population.

But he said the programme was bigger than just Parininihi.

"As we strengthen and expand our pest control work and increase native populations, biodiversity corridors can be created connecting our work to other projects", Davis said.

Volunteer Phil Andrews, of Shell Taranaki, will be on the ground helping with the catching this week.

As well as having a work connection with the project through the Trust's sponsor, Shell, Andrews also has a personal connection with his family once owning a farm at the very end of Whitecliffs.

He lived on the farm until he was four years old and can recall the bush disappearing due to possums.

"It's great to see this being reversed and the bush being restored and kōkako returning after 30 years of extinction," he said.

Amanda Rogers, one of the technical specialists, said the biggest challenge with catching the birds was encountering enough calm, fine weather.

"The Rangitoto Range is the highest in elevation of any place we've caught kōkako and it tends to be windy and wet," she said.

"One of our net sites is 900m above sea level, and we've already had a snowfall this April."

She said it was no easy feat nabbing the birds, with the task usually requiring about five people to run a catching attempt.

There were many jobs involved, including surveying tracks for kōkako, tree climbing, slingshot firing, chopping and rigging sites and luring the bird into the net.

"A​nd not least of all, distracting kōkako with a delicious banana while they receive coloured leg bands."