For the veteran searchers seeking signs of the long-lost South Island kokako, a valley east of Puysegur Point in Fiordland National Park sounds like a breakthrough.

The bird was believed extinct in the 1960s, a tuneful victim of predators and loss of habitat.

But the South Island Kokako Investigation Team has kept compiling reports of the grey bird with distinctive orange wattles at each side of the beak. The North Island kokako has a bluish wattle.

And now an offshoot of January's hunt for more kakapo in Fiordland has led to hopes that the team has another valley to check in detail, with a community of the supposedly extinct birds living there.

For Christchurch researcher Ron Nilsson, the breakthrough has come after more than 20 years of collating reports and checking regions in Nelson, the West Coast, Fiordland and Stewart Island.

He went to the other valley, on the South Island's south coast, when the search for more kakapo had ended without success.

A team was dropped in by helicopter to check out reports they heard from a geologist remapping Fiordland. The map maker had provided grid references.

"We landed at 1pm and by 2pm we had heard the first of the calls," said Mr Nilsson. The calls kept coming in sequences of about five, and up to 10. They heard at least 50 calls in the first afternoon.

Some recordings were made and better gear was set up next day, but it proved to be the hottest day of the summer in Fiordland and the forest went silent.

Mr Nilsson believes the concentration of calls in such a confined area indicates a possible viable breeding population. The abundance of calls indicates the birds are actively calling to mates and marking out territories.

In recent years, searches for the South Island kokako have been in Granville State Forest in the West Coast's Grey Valley and further north in the Paparoa Range near Charleston.

"In those places there may be one or two birds in 5000ha of forest. This one is different. I think there is a small group of birds there. You have got a sense that it's very important."

The group was in the area for just over a day, but accomplished a lot in that time. Now the pressure is on to convince the Department of Conservation - or a sponsor - that an urgent return visit is necessary.

There has been a tussock mast and a beech mast - a year when those plants produce much more seed than normal. That will bring a rise in the number of mice, and then an increase in the predators that feed on the mice.

When the mice run short as a food source, the predators - rats and stoats - may start eating native birds and the fragile group of kokako may be vulnerable.

The concentrated activity near the landing site meant the second grid reference point nearby had not yet been checked.

"These were very encouraging signs," said Mr Nilsson.

What is a Kokako?

* A member of the New Zealand wattlebird family, which includes the North Island and South Island kokako and the extinct huia.

* North Island kokako have blue wattles below their beaks. There are fewer than 400 pairs left.

* South Island kokako have orange wattles. They are assumed to have died out in the 1960s but may have survived in small numbers.