A group of people have captured the call of what some believe is the South Island Kokako.

The last verified sighting was a decade ago - after having not been seen since the 1960s.

Trustee Inger Perkins said a group believed they captured the sound of the bird in Grey Valley recently.

A six second clip of three descending notes embodies the haunting quality of the bird's signature call.

"Our experts believe it is, but we've said in the past that the sound recording isn't the definitive evidence that we need, but it's certainly really strong evidence."

The South Island Kokako Charitable Trust released a wanted poster for sightings of the bird - with a reward of $5,000.

The reward has since been doubled to $10,000 earlier this month. 

Perkins said they've further received up to 50 encounter reports, of which experts are getting excited about.

"Some of them are in recent months and recent years, but some of them are quite a bit older.

"We're finding that people might have reported it some years ago when the birds were still thought to be extinct, so they were turned away by the Department of Conservation."

Perkins said they're hoping for some photographic evidence so conservation can kick into action.

LISTEN TO WHAT COULD POSSIBLY BE THE BIRD CALL ABOVE