Project co-ordinator Richard Robbins said, going by the photo and the bird's behaviour, there was a "reasonably high" chance it was a juvenile that had hatched on Moturua in spring.
Before the reintroduction, kakariki occasionally visited the Bay of Islands but their prospects on the mainland was dismal due to predation and the difficulty of finding a mate at such low population densities.
In recent years, however, their prospects had improved due to pest control. The kakariki was spotted in an area of "very effective" pest management by community group Bay Bush Action, Mr Robbins said.
Meanwhile it appeared the birds released on the island had a good breeding season. Late last month motion-activated cameras had captured the first island-hatched fledglings feeding with their parents.
You're on candid camera: Video of the first fledglings hatched on Moturua Island making the most of a millet-seed feeding station:
It was clear they had been hatched on the island because, unlike the birds translocated from Hauturu (Little Barrier), they had no leg bands.
Unlike other species released on to the islands as part of Project Island Song kakariki were able to fly away, but at least 35 were still on Moturua.
''We always knew some of the kakariki would either visit or disperse to the mainland, and over time once the islands are full of kakariki we hope that they will also become a common sight on the mainland too,'' Mr Robbins said.
It was vital, however, that a self-sustaining population established itself on the islands first. Project Island Song volunteers had set up feeding stations and nesting boxes on Moturua to encourage the birds to stay.