Dean Baigent-Mercer, conservation advocate for Forest and Bird, said the return of kakariki was "hugely significant".
"They've become extinct on the Northland mainland in our lifetime. Occasionally they do fly over from the Poor Knights or the Hen and Chickens, but as far as we know they haven't nested on mainland Northland since the early 1980s."
In the 1880s kakariki were so common their feathers were used to stuff mattresses, he said.
Unlike other birds re-introduced to the islands kakariki could easily fly to the mainland so they could become a common sight in backyards around the Bay, travelling in flocks and making a "cheerful chatter". On the mainland, however, they would be vulnerable to predators.
"So it's up to all of us if we want kakariki back in our everyday lives," he said.
The mainland Bay of Islands had a chain of pest control projects from Purerua Peninsula in the north all the way around to Rawhiti. However, there were still gaps, and everyone could contribute by trapping rats and possums in their own gardens, or by joining a pest control project targeting the four worst offenders - possums, rats, stoats and feral cats.
That not only benefited kakariki but also boosted numbers of tui, grey warblers, kukupa and ruru (moreporks).
"We have only the crumbs of what there used to be ... With pest control we can increase the number of birds that are around and bring back the ones we've lost."
Kakariki made their nests in holes in trees or banks and could be prolific breeders, laying several clutches of eggs in spring and summer with three to nine eggs per nest.
That meant numbers could increase quickly if predators were absent, as shown by saddlebacks on Urupukapuka and Moturua. They were only re-introduced in 2015 but were "absolutely everywhere" on the islands.
