NZ's unique native frogs 'just hanging on'

New Zealand's three native frogs have endured in our wilderness for tens of millions of years - but now the tiny amphibians are close to the brink, a new stocktake has found.

"Our frogs are just hanging on, there's no doubt they're still in grave danger," Conservation Minister Eugenie Sage said of a status report published today.

The Archey's, Hamilton's and Hochstetter's frogs were markedly different to all other frog species on the planet, and had barely changed in their 70 milion years here.

"They don't croak like most frogs, they hatch as 'froglets' – almost fully formed frogs – rather than tadpoles, and their pupils are round rather than slit-shaped," Sage said.

The male Archey's frog carried his offspring on his back.

Archey's frog, meanwhile, had an improved status from "Threatened – Nationally Vulnerable" to "At Risk – Declining".

But this change was due to a better understanding of likely population trends, rather than observed increases in their populations.

As with other native species, predators and habitat loss were threatening frogs with extinction, and current conservation efforts were helping the species.

Eleven Hochstetter's frog populations previously assessed separately had been combined into a single assessment for the report, following new research that indicated their genetic distinctiveness was not sufficient to consider them as separate species.

Despite the merger, Hochstetter's frog was still classified as "At Risk – Declining", reflecting the ongoing decline anticipated across all Hochstetter's frog populations.

The most widespread native frog, and found across the upper half of the North Island, the species was the most aquatic of the native frogs.

It was generally dark brown, grew up to 48mm long, had partially webbed feet and had more warts than the other native frogs.

Hamilton's frog, the largest native frog, growing up to 51mm long, had changed from "Threatened – Nationally Critical" to "Threatened – Nationally Vulnerable".

That was due to new genetic research indicating that two frog populations on different islands - the Hamilton's frog and the Maud Island frog - were actually one species, despite earlier being considered separate.

The species continued to survive as original populations only on Takapourewa/Stephen's Island in Cook Strait and Te Pakeka/Maud Island in the Marlborough Sounds, where it was carefully managed by the Department of Conservation (DoC).

Fossil records showed the Hamilton's frog was once spread from Waikato to Punakaiki.

DOC has established populations on other islands as insurance against a disaster, such as a fire or pest incursion wiping out the remaining populations.