Forty odd years ago, rangers up in the Brindabellas couldn't hear each other speak over the loud croak of northern corroboree frogs on the night air. Then in the 1980s, the chytrid fungus reached Australia, spreading an infection now responsible for wiping out hundreds of frog species world-wide.

Today, fewer than 200 northern corroboree are estimated to survive in the wild, with their southern counterparts already listed as critically endangered.

After scientists rescued scores of northern corroboree frog eggs from the 2003 firestorm that ripped through their habitat, Tidbinbilla nature reserve became ground zero for the nation's largest breeding program to try to save the species.

But, fresh from releasing another 600 young adult frogs into the alpine wetlands of Namadgi on Tuesday, scientists say the species is still facing a perfect storm of threats including climate change.

Peter Cotsell from Namadgi and Tidbinbilla national parks said reduced rainfall, past human activity in the area including mining and now the fungus meant local populations were still low 16 years on from the bushfires.

"We've got frogs still out there, they're surviving but they're not growing," he said. "They're struggling."

The fungus, which eats away at a frog's vulnerable skin, is often carried into habitat by humans, on boot soles and car tyres.

Researchers believe it spread through the African clawed frog, which was shipped all around the world for use as the first mainstream pregnancy test between the 1930s and 60s - after a zoologist discovered injecting the urine of a pregnant woman into the amphibian caused it to ovulate.

At the time, the test was considered 98 per cent accurate (two researchers remarked that, when comparing the diagnoses of two experienced doctors and the frog, "only the frog was correct").

As different tests were developed and the frog species found its way into new habitats, so did the fungus.

Tuesday's corroboree release was the largest since 2014 for the Canberra program, which has also been releasing eggs into the wild in the hope they might develop a resistance to the fungus. At least one pair of frogs have since successfully bred in the wild.

John McRae, an ACT ranger of more than 12 years, said researchers were now looking at how frogs might be adapting to the threat, including sunning themselves more often to potentially kill the fungus through heat.

The frogs are slower to mature than many other species and, when the breeding program began at Tidbinbilla, he said the team was forced to get "experimental".

"We had to try a few things, different temperatures, different ambience, you know, play some music," he laughed.

"You don't just whack a few frogs in a tub and hope they hop to it. Actually [this species] don't even hop, they walk."

Mr Cotsell said the program had now evolved into semi-wild outdoor enclosures, where frogs were growing bigger and stronger than those bred indoors.

The markings of each frog's belly are as distinctive as a finger print, and help the team keep track of those released. Of course, that's not the only method.

"When we do a [ground] survey, we call and the frogs call back," Mr McRae said.

"We literally call out 'Hey Frog!' loud and sharp and the frogs give us like a startled alarm call back."

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