The Guardian: Back from the brink of extinction: hunting for the world's rarest frog

by Oliver Milman

March 9, 2015

If you’re planning on scouring a vast Australian mountain range looking for what is probably the rarest frog in the world, scientists suggest a rudimentary approach works best.

“We shout out ‘hey frog, hey frog’ and listen for a call back,” says David Hunter, a threatened species officer at the New South Wales state government. “I hate to think how many times I’ve shouted that out.”

A more technological approach – camera traps, for example – wouldn’t really work given the endangered southern Corroboree frog measures just 3.5cm in length.

The frogs – the females are largest and pear-shaped when carrying eggs – are coloured by flashes of bright yellow as a warning to predators of the toxins developed from the gobbling up of ants. But the frogs aren’t fully visible unless you stoop down for a close look.

The other key difficulty in finding the frog is the vanishingly tiny numbers of the species’ population. In January, Hunter and his team found there were just four frogs – two male, two female – in Kosciuszko national park in the southern part of New South Wales, its entire range.

Such a miniscule band of wild survivors – four in the entire world – means the southern Corroboree is “effectively extinct”, Hunter says.

But the combined effort of Australians academics, zoos and governments mean that the frog is being dragged back from the brink – with potentially huge implications for other amphibian species around the world that have been decimated by a deadly fungus.

Chytrid fungus has spread across six continents and has been blamed for causing the decline or extinction of around 200 frog species since the 1970s. In Australia, six frog species are thought to have been wiped out by the fungus, which is carried in water and by other frogs. The fungus causes a disease called chytridiomycosis on the skin that fatally impairs frogs’ ability to maintain electrolyte, water and oxygen levels.


The southern Corroboree frog was seemingly destined to be its next victim. But a pioneering collaboration has seen southern Corroboree frog numbers steadily climb in captivity, with last week containing an important milestone in a plan to reintroduce the animals back into the wild.

Amphibian experts from Melbourne Zoo and Sydney’s Taronga Zoo, along with NSW government wildlife officials, released 80 frogs into an enclosed, fungus-free area of Kosciuszko national park. 

The release, the first time that adult Corroborree frogs have been reintroduced back into the mountains that once teemed with millions of the animals, could mark a key turning point in the global effort to reverse plummeting amphibian numbers.

“This is huge, it doesn’t get any bigger for frog people,” explains Jon Birkett, head of Melbourne Zoo’s reptile house.

Birkett has been carefully nurturing Corroborree frog numbers since the 1970s, initially in fish tanks and now in more sophisticated quarantined premises that prevents any chance of the fungus reaching the frogs. Melbourne now has 196 frogs, while Taronga has more than 400.

The idea is that if the released frogs can survive and thrive in the enclosures, their copious offspring – females can lay up to 30 eggs at a time – could be reintroduced more widely and help develop better resistance to the fungus, which entered the Kosciuszko region in the 1980s.

“We can facilitate the co-evolutionary relationship between the pathogen and the frog to produce more resistant animals,” says Hunter. “Just by keeping these frogs alive in the wild, we’ll be producing healthier, stronger animals and help the evolution of them alongside this pathogen.

“It’s hugely exciting. We don’t see having the frogs in captivity as an adequate end point for this species. We need to have them back out in the wild where they are part of the ecosystem.”

Hunter said the released frogs’ offspring could be distributed more widely within a year and, if successful, the colony would represent a breakthrough in the effort to reverse the worrying decline of many frog species.

“This pathogen is a global problem and anything we can do here can be applied elsewhere in the world,” he said. “It has huge potential. Keeping animals in captivity is resource intensive and here we are trying to maintain frog populations at very low cost. If it works, it’ll look after itself. It is, as far as I’m aware, a world first for an endangered frog.”

Frogs are often overlooked in what’s termed the sixth great extinction event that is sweeping the globe. Large mammals – tigers, polar bears, orangutans and so on – tower over amphibians in both stature and the public’s spasmodic attention on conservation.

But times are desperate. About a third of the world’s amphibians are now endangered, according to the International Union for Conservation. Climate change, as well the chytrid fungus, poses a major risk to frogs, especially for the likes of the southern Corroborree, which lives in an alpine region and may struggle to adapt to a warmer, dried out environment.

Without really knowing much about it, Australia, and the world, is losing some incredible creatures. For example, the fungus has already killed off the gastric brooding frog, a creature that swallowed it eggs, developed its young in its stomach and gave birth via its mouth.

The next year or so will give a clearer indication whether the southern Corroborree will become another lost species or whether an improbable, almost audacious, recovery effort can be pulled out.

“I’m personally optimistic that we can have them back out into the wild in good numbers,” Hunter, who has worked on the issue for 18 years, says.

“We have such a unique environment in Australia so it’s a huge tragedy to think that future generations might not have the opportunity to experience remarkable animals like the Corroborree frog in the wild.

“I really think that would be a massive loss to humanity.”

haggadah Section: -- Ten Plagues