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The South Island kokako is now listed as officially extinct, but one of its most dedicated fans is still a believer.

Ron Nilsson, of Christchurch, has spent more than 20 years searching for the South Island kokako, which he says he has heard up to 100 times and seen once.

Conservation officials yesterday formally declared the South Island kokako extinct, saying there had been no confirmed sightings for more than 40 years.

But Mr Nilsson said he saw a bird just five years ago in Westland.

"I watched the bird flit across an old forestry road."

Mr Nilsson, a self-taught bird expert who has worked for the Wildlife Service, said he knew it was a kokako because of its size and behaviour.

"They are bigger than a tui ... like a small native pigeon. It has a peculiar body movement, like a saddleback."

Mr Nilsson said some of his colleagues had also seen and heard the elusive bird.

He planned to get back into the Fiordland bush in the next month to continue his search.

He has also searched remote valleys in Nelson, Westland and Stewart Island for signs of the grey bird with orange wattles at each side of the beak.

"There are half a dozen places where it could be."

He said that unlike the Department of Conservation, he would not have the audacity to say something was extinct.

"They are just saying that so they don't have to spend money and take the time and effort of looking for it. They are covering their bottoms, really."

In a reverse decision, DoC removed the New Zealand storm-petrel (Oceanites maorianus) from the extinct list after a population was discovered in the Hauraki Gulf in 2003.

Rod Hitchmough, a scientific officer at DoC, said the kokako decision had attracted controversy but it was probably extinct years ago.

Mr Hitchmough, who compiled DoC's latest lists of threatened species, which also declared six native insects and snails extinct, said the kokako was last seen in the South Island in 1967.

There had been further reports on Stewart Island in 1987 and other more recent but uncorroborated sightings.

The North Island kokako population is endangered, with fewer than 400 pairs.

Conservation Minister Chris Carter said the new threatened species list updated the "threat classification" status of 5819 of New Zealand's native plants and animals, and 44 had been given a significant change in status.

Almost half of those were listed in one of the seven threatened categories, and the rest required further research to determine if these were threatened or not.

"Some have improved, like the crested grebe and black petrel, and others, such as the grey duck and rifleman, are more endangered," Mr Carter said.

"It's a wake-up call for us, as a country.

"Human-induced threats and the introduction of predators and pests continue to plague our native species," he said.

"The species that make up our country - the unique bird, reptile, plant and insect species that are endemic to these islands of ours - are what helps to make us New Zealanders, give us a unique place in the world and give us our identity."

Settlement of New Zealand by Maori and Europeans had made an incredible impact on the nation's biodiversity, the minister said.

The total number of threatened species reported in the new list rose by 416 to 2788 - in many cases because new information had become available since the lists were last reviewed in 2002.

Another 984 species have been listed as "data-deficient".

Mr Carter said the list would be used to prioritise management of threatened species.

The battle to retain biodiversity was not only about resources but also depended on expertise in developing management plans and providing the science for managing threatened species.