Two faint bird calls in Kahurangi National Park may have revealed location of elusive South Island kōkako

Two faint bird calls in the Kahurangi National Park may have revealed the location of the elusive South Island kōkako.

But to be sure, experts need more proof and they're offering $10,000 for it.

Deep inside the thick forest of the Kahurangi National Park near Nelson is a resident who hasn't been seen in 50 years. The South Island kōkako.

"We're pretty confident simply because of what they're hearing and seeing around that site," South Island Kōkako Charitable Trust general manager Inger Perkins told Newshub.

"So what the kaka are doing, what the tui are doing.

"The softness of it, the melancholy nature of it, that seems to say kōkako to me."

The strongest suggestion yet of its existence is taking flight thanks to a sighting and audio recording made along the Heaphy Track just two weeks ago.

Experts played the call back to a kaka to gauge their response. It's left them close to 100 percent sure it was the South Island kōkako.

"From the structural point of view yes," Trust advisor Rhys Buckingham told Newshub.

"From the fact that the kaka didn't respond to it a bigger yes and the fact that he had that associated sighting."

With its distinctive yellow and orange wattle, it's different to the blue wattled North Island kōkako which has a population of more than 1600 pairs.

The last confirmed sighting of the South Island kōkako was in 1967 after which it was believed to be extinct.

"Reports of seeing the bird in the forest near Reefton back in 2007 meant that DoC changed their classification from extinct to data deficient," Perkins said.  

That's where the public comes in and the Trust is asking trampers to keep an eye and ear out.

They're offering a $10,000 reward to confirm the South Island population is still flying.

Watch the full story above.