More than 3,000 critically endangered Baw Baw frogs have been released in Victoria’s east as part of a record-breaking conservation breeding program.
Zoos Victoria’s reintroduction of 3,000 tiny froglets and 40 adult frogs into the high-altitude forests of the Baw Baw plateau, about 120km east of Melbourne, was the largest in its breeding program for the species.
With fewer than 500 individuals remaining in the wild, Deon Gilbert, a threatened species biologist with the zoo, was hopeful many of the new recruits would survive and bolster the dwindling population.
Releasing the tiny froglets – roughly the length of a grain of rice and carefully reared by the zoo’s specialist amphibian keepers – was nerve-racking, Gilbert said. “You just hope for the best for all of them. It’s up to them from there.” Adult frogs measure up to six-centimetres long.
Once abundant, the species – found only on a “really small patch of real estate on the Baw Baw plateau” – had suffered a 98% population crash mainly due to a disease called the chytrid fungus, Gilbert said. They also faced overlapping threats due to climate change, historic logging practices and development.
Dr Kirsten Parris, a professor and amphibian ecologist at the University of Melbourne, said the Baw Baw frog was one of the rarest of Victoria’s 38 frog species. Very few people had heard or seen the “super cute” and “chunky” frog, she said, given its small distribution in a relatively remote part of the state.
No Baw Baw frogs were recorded in a recent citizen science frog census called Frog Month Victoria, she said, which received more than 1,200 records of frog calls from all parts of the state. They did, however, receive some calls of another nationally listed species – the vulnerable growling grass frog – from parts of Melbourne and the Bellarine peninsula.
Baw Baw frogs had developed some specialised reproductive strategies, Parris said, which made it harder for populations to recover from threats such as chytrid fungus.
“It lays eggs in little nests in moist areas. The tadpoles have a semi-terrestrial life and then turn into little frogs,” she said.
They put additional effort into making their eggs, but lay fewer – about 100 – compared with more common frogs, such as the pobblebonk frog that lays more than 1,000.
In the wild, the Baw Baw frog’s entire reproductive cycle happens underground in the absence of sunlight, Gilbert said. Tadpoles, which are “pure white” from the lack of sunlight, survive thanks to huge yolk sacs.
It could take four to six years for recently released froglets to reach maturity, he said. If they survived to adulthood, some might live up to 15 years old.
Gilbert was quietly optimistic the new batch could help bolster wild populations, after successfully returning smaller numbers of frogs in recent years. A recent survey undertaken at a trial release site – a patch of suitable habitat where no wild Baw Baw frogs had been recorded – revealed the zoo-bred froglets were capable of surviving in the wild.
“I couldn’t believe it, to be honest, when we went in to start surveying and were having all these frogs call back at us for the first time,” he said.
Finding frogs in the forest was “almost impossible”, Gilbert said, particularly Baw Baws, which had a penchant for hiding under soil and leaf litter. So to help with tracking, the adult frogs were released fitted with radio transmitters attached to a small belt around their hips.
The team would also rely on their trio of specialised wildlife detection dogs – Kip, Finn and Sugar – who were trained to systematically sniff out Baw Baw frogs and sit calmly until their handlers and biologists confirmed the discovery.
The zoo’s recovery team plan to check in on the latest arrivals in October, during a small window of time when male Baw Baws would be calling. It will be a long wait until then.
These types of recovery programs were a “lesson in patience”, Gilbert said, adding it was important to share hopefulness and optimism when things were going in a positive direction.
