Now, almost 25 years later, the two kōkako share their Hunua Ranges home with 105 other breeding pairs.
He also acknowledged public backlash to the use of 1080 poison to rid the site of pests as one means to achieve that end.
In September 2018, the Friends of Sherwood Trust brought an injunction in a bid to stop Auckland Council and the Department of Conservation from dropping 1080.
In an Environment Court judgment, Judge Melanie Harland said she didn't believe there would be "serious harm" to the environment if the poison was distributed throughout the area.
The judgment gave the green light for the drop to go ahead as planned in the Hunua Ranges Regional Parklands, Whakatiwai and Waharau in late 2018.
"The preliminary results say that we have had a massive impact on the rat population, in a way that we couldn't have done, realistically or practically, with any other mechanism," Goff said.
"I think all of us want to have a legacy where we leave our environment better than we found it."
Goff said Auckland Council would need "every mechanism available" to achieve its goal of being predator-free in 2050.
One challenge the Hunua Ranges project faced in the beginning was teaching the native New Zealand birds a new dialect.
"We had one breeding pair to begin with so we needed to create a greater genetic diversity," Ward said.
"Those birds came from the King Country, but the interesting thing about kōkako is they have different dialects.
"So to anchor those birds here, to maintain them in this location, we needed to play their dialect [on loud speakers] so they didn't get scared away by the Hunua birds.
"That happened for the first few years until we started to build a population and it was self sustaining in the Hunua Ranges."
Ward said the same thing would need to happen in the future if the Hunua Ranges were to become a kohanga for other areas establishing kōkako.
"As we build up the population, we would hope to have birds move from here to other locations."
Declan Morrison, who manages the Kōkako recovery project, said the greatest reward was seeing nests he had watched daily eventually fledge chicks.
"They're a particularly special bird. They look better than most of them and they sound amazing."
He said rat numbers had a very tangible effect on the project's success.
"As soon as the rat numbers get low enough, the fledgling success rate just goes through the roof," Morrison said.
"The rats are quite good climbers because they're ship rats. So they will climb up the nest, scare off the parents and eat the eggs or chicks, and the odd parents as well, if they're hungry enough."