The mōhua (yellowhead) bird's numbers have risen dramatically, while other native bird numbers have doubled in the 21 years since 1998, the Department of Conservation (DoC) says.
Results analysed by DoC show numbers of mōhua have gone from just 14 birds to 444 in the latest study undertaken, in November 2018.
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Numbers of tuī, bellbirds, and several others had also steadily increased.
DoC principal science advisor Dr Colin O'Donnell told Newshub the yellowhead had disappeared from about 90 percent of the South Island's forests.
"Now, they're still in a few sites. [There's] a small population in the Marlborough Sounds we've re-established, there's a population we're trying to recover in Arthur's Pass, and then some on the offshore islands of Fiordland and Aspiring National Park."
Dr O'Donnell said successful predator control had re-established populations on the mainland.
According to DoC's website, in the 1800s, the mohua was one of the most "abundant and conspicuous" of New Zealand's forest birds.
DoC says with the arrival of Europeans came forest clearances and the introduction of new predators, causing numbers to decline.
The mōhua's fluorescent yellow colour made it a "stunning bird", Dr O'Donnell told Newshub - but because it rests in tree holes, it's more vulnerable to predators.
He said it was exciting to see the increase in numbers.
"That's very gratifying to see [that we] can recover a bird back close to before humans came to New Zealand," he told Newshub.
The mōhua have also bred in captivity at Orana Park in Christchurch, DoC says.