Spotted tree frog

The spotted tree frog belongs to an ancient group of ground frogs who were already hopping through Gondwanan rainforests, some 40 million years ago.

As Australia tore away from Antarctica and slowly drifted north, it began to dry out, and the cool, moist rainforests shrank. Relict species like ancestors of the spotted tree frog sought refuge in the south-eastern temperate mountain forest streams, amongst the elevated peaks and plateaus of the Southern Alps and great eastern escarpment.

Then, in the 1960s, something started going very badly for the spotted tree frog. First came the introduction of tadpole-devouring trout. But the real killer was the arrival of frog chytrid fungus. This devastating global disease clogs a frog’s skin, affecting their ability to breathe.

Historically the NSW population of spotted tree frogs was known from just two streams, in the Upper Murray and Upper Swampy Plains catchments of the Snowy Mountains. By 1998 one of these populations in Kosciuszko National Park had completely disappeared, and the last remaining frogs were succumbing to chytrid infection.

In the summer of 1998, research scientists undertook an emergency rescue operation to collect frogs for captive breeding. They found the remaining wild population in Kosciuszko had just a solitary, lonely male frog, his unanswered mating calls resounding through the catchment. He was the last wild spotted tree frog left in NSW.

The long-term survival of the NSW population now rested on the warty shoulders of this sole surviving male frog (who researchers named ‘Dirk Diggler’, after the movie Boogie Nights). With breeding partners sourced from across the Victorian border, Dirk began what would become a decades-long captive breeding operation at the Amphibian Research centre in Melbourne to repopulate wild spotted tree frogs into their former habitat.

Initially, captive-bred frogs thrived after being released back to the wild. Sadly, it wasn’t long before Dirk’s offspring faced infection from chytrid fungus, which once again decimated their numbers in the wild.

But chytrid has a weakness. It doesn’t like environments with temperatures over 28 degrees C. So, in 2014, researchers started an experimental wild colony of spotted tree frogs in a new catchment, with warmer conditions. To everyone’s delight, they thrived.

The higher temperatures of the catchment, along with the frogs’ habit of sun basking on warm rocks along the river, have kept this new population disease free.