The South Island kokako was last sighted in 1967 at Mt Aspiring and was officially declared extinct in 2007.
But although the 'grey ghost' was officially declared extinct there are some who will not accept it has gone for ever - and they swear they have heard and seen it.
Secretive and ilusive, few have heard the bird's haunting organ call and even fewer have seen its grey plumage and bright orange wattles.
But Rhys Buckingham is convinced the bird is still alive, and he has spent the past 36 years scouring some of the most remote parts of the South Island trying to find it.
Asked whether he believes the bird has been written off too early, Buckingham said: "definitely yes". For years he has been a lone voice but lately some big names in the animal world have added their weight to the claim that the extinct bird could possibly be one of the rarest creatures on earth.
Ruud Kleinpaste, better known as the Bugman, is a trained ornithologist and is adamant he saw a kokako in south Westland as recently as last February.
"I was driving down the road, just south of Haast... and there was this bird with a very labouring flight and long tail, short rounded wings and I thought to myself you are dreaming. I wound down the window and that is when I hear the sound of a kokako."
Kleinpaste said the sound of a kokako is unmistakable and once you've heard one, he says "you will never forget it".
The South Island kokako has red wattles instead of blue and is secretive and shy about breaking into song.
"A South Island kokako vocal, there is a sense of unreality simply because this isn't supposed to happen. They're supposed to be extinct," Buckingham said.
Experts say the ability of the birds to be right in the midst of people and be invisible is extraordinary.
Over recent months there have been a cluster of sightings in South Westland and Buckingham said there's no reason for the bird to have left.
"They take territory and they'll stay there."
Opinions are divided about the best way of proving the birds really are alive. One radical suggestion is to shoot a bird because there is a much better chance of getting a definitive identification with a shotgun than with a camera.
And Buckingham cannot understand why the bird is so quiet.
"It's a songbird, it's got a voice, it's got a remarkable voice," he said.
Those lucky enough to have seen the bird all agree it was simply a case of right place and right time.
Kleinpaste said they are very illusive birds and they can see you before you see them.
Buckingham claims to have seen the bird, and just over a year ago recorded its song. But he hasn't been able to get a photo and he's not alone. In 140 years, the illusive bird has never been photographed or filmed in the wild.
"To have... some recordings of a bird and to get the glimpse of
a bird does give me a lot of hope. That bird's still there, we've
got the means to get it, one day our luck will change and we'll get