North Island brown kiwi on rise in NZ

Conservationists in New Zealand are revelling in the first recorded increase in the North Island brown kiwi population, reversing decades of plummeting bird numbers.

Until the latest expert assessment of New Zealand's birds - which are conducted every five years - each kiwi species has been categorised as vulnerable or worse.

However, the latest report moves the North Island brown kiwi from "At Risk - Declining" to "Not Threatened".

For Save The Kiwi trust executive director Michelle Impey, it's exciting to reach the conclusion that efforts to rebuild the population of NZ's iconic native species are working.

"For everyone that's doing the work, it's a huge endorsement," she told AAP.

"For the first time in the history of this program that we've been able to save they're no longer going down, we have a prediction they're going up. It's hugely significant."

Department of Conservation principal science advisor Hugh Robertson goes further, estimating the species has already grown from a low watermark of 25,000 birds, back up to about 27,000 to 28,000.

"It's fantastic ... Just really great for the kiwi that they've turned the corner. Still a lot of work to do, but they're out of the threatened category," he told AAP.

Dr Robertson has spent three decades monitoring and caring for NZ's unique birdlife and is the lead author of the assessment.

His estimate is that one million kiwis would have roamed NZ prior to human settlement, showing the savage impact of introduced species and habitat loss.

The five species now number about 75,000.

"When I started doing kiwi research we don't even know what the threats to kiwi were," he said.

"If you'd asked people 30 years ago, 'What are the threats?' you'd say habitat loss and dogs ... we just really didn't realise that stoats and ferrets was such a big problem."

Dr Robertson says the credit for the turnaround must go to thousands of New Zealanders invested in saving the country's favourite bird: keepers, trappers, scientists, donors, landowners and more.

A number of strategies have been crucial, including predator control.

Kiwis flourished prior to human settlement, when the only mammals in New Zealand were bats.

European settlers brought a wide array of pests and invasive species, including stoats, ferrets, rats and possums, all of whom kill kiwis and other native birds before they develop.

"Stoats are the number one problem for kiwi chicks, so trapping efforts are aimed primarily at stoats and also ferrets where ferrets are," Dr Robertson says.

The deployment of 1080 poison is particularly effective as "rats will also eat the baits, and then stoats will eat the possum carcasses, so they get a secondary poisoning dose".

Another strategy is Operation Nest Egg, a nationwide program which sees kiwis hatched and reared in captivity and fenced sanctuaries until they're big enough to fend for themselves.

The program, at great expense and effort, increases the likelihood of hatched chicks reaching adulthood from five per cent to 65 per cent.

Once kiwis reach about one kilogram in weight, they're considered sturdy enough to take on stoats, and are realised into the wild.

Dr Robertson said some of the volunteer efforts were inspirational.

"Hundreds of community groups are trapping and poisoning predators all around the North Island and and the results of their work is seeing increases again," he said.

"In Taranaki ... they've now got something like 1300 pairs of kiwi.

"On the Coromandel Peninsula, lots of community groups there are seeing really positive growth and a doubling or tripling of the population there since we started management back in 2000."

Local dog owners have also heeded the call, restraining their pets to allow the native birds to flourish.

"In one big project at Whangarei Heads, the population has gone from that 200 birds to over 1000," Dr Robertson said.

"Dogs can wipe out a population really quickly, but the whole community there is really supportive.

"If anyone sees a dog wandering without on a lead or the owner attached, they stop and say 'you need to tie your dog up', or they grab the dog and return it to the owner or to the pound."

The growth in numbers comes with an important caveat: the North Island brown kiwi is now rated "Not Threatened" but still requiring conservation support.

Ms Impey said all five kiwi species still needed support to flourish.

"This is a very good indicator but ... the niggling fear is that people have the view that the job is done. It's far from that," she said.

"We rely on sponsors and donors. We need to take this as a pat on the back and to keep going."