RNZ's Morning Report birdcall has helped solve a mystery about grey-backed storm petrels in Fiordland.

The grey-backed storm petrel, one of New Zealand's smallest seabirds, are found around the southern ocean in subantarctic waters.

While they tend to stay close to colonies after breeding, there have long been rumours of a breeding colony in Fiordland.

A clue to where the storm petrels might breed within Fiordland was revealed in March 2019, when a passive acoustic recording device used to monitor kiwi calls picked up several mystery bird calls.

Bird expert Dr Colin Miskelly gave a presentation on Sunday about how the birds were ultimately found, and the surprising role Morning Report's daily bird calls had to play in their discovery.

Bird expert Dr Colin Miskelly.

Miskelly told Morning Report on Tuesday that a sound file of the mystery bird call ended up on his desk and although he had never heard it before, he guessed it was the grey-backed storm petrel.

In February 2020, he organised through the Department of Conservation to take a dog, trained at finding birds, to Fiordland but nothing was found.

He suggested this was because stoats had reinvaded a number of islands in the area at this time and it was possible they had "mucked up" any chance of finding the birds.

In 2022, the mystery bird call was again picked up on a recording device which let experts know the birds were still there.

Grey-backed storm petrel on Rangatira Island, Chatham Islands. Photo: SUPPLIED / Colin Miskelly

Two months later in May, Miskelly said he was listening to the Morning Report birdcall, as he always did, and the mystery bird call featured.

He managed to find out it was indeed a grey-backed storm petrel that had been recorded on a remote island within the Kerguelen Islands in the Indian Ocean in 1987.

Miskelly said Morning Report was given the recording in 2014 but it had taken until 2022 for it to be played.

The riddle was solved, he said.

"It was the same call we had recorded in Fiordland and it confirmed that this is where the storm petrels are. It's great."

Miskelly said there was still a bit of work to do.

Experts would have to return to the site, located the birds, find out how many there are and if they are doing OK.

The island they were believed to be on was one of the "best places" possible in Fiordland for them to choose to breed on as threats by stoats, for example, was low.

Reproduced with permission