Return of the Frog: Conservation Breeding Gives the Southern Stuttering Frog a Way Home

The temperate rainforests of eastern Australia once echoed with the call of the Southern Stuttering Frog. But the same cool, moist conditions that make these forests ideal habitat also favour one of this species' deadliest enemies, the amphibian chytrid fungus. This devastating disease has driven catastrophic declines in frog populations worldwide [1], and the Southern Stuttering Frog has been one of its many victims. Today, the species has disappeared from almost two-thirds of its former range [2], but a new recovery program [3] hopes to safeguard the species from extinction and return frogs to their former range.

The Mission

Australia ranks among the highest countries worldwide for biodiversity loss, with declines exacerbated by contemporary climate change and natural disasters, including drought conditions and bushfires. In response to the widespread destruction caused by the 2019–2020 mega fires that devastated wildlife along the east coast of Australia, the Australian government provided vital funding for rehabilitation and recovery efforts. The Symbio Conservation Foundation was one of nine organisations nationally to receive funding to establish state-of-the-art conservation facilities for captive assurance populations and Conservation Breeding Programs (CBPs) for threatened species. The Southern Stuttering Frog, Mixophyes australis, was among these species, with a CBP established at Symbio Wildlife Park in 2022 following construction of a carefully designed, purpose-built facility [3]. The mission was to establish an ex situ assurance population, achieve successful reproduction, and reintroduce the species into the wild in areas where it has gone extinct.

The Species

The Southern Stuttering Frog, Mixophyes australis, was originally considered to form the southern clade of Mixophyes balbus, but was determined to be a distinct species in 2023 [4]. The species is experiencing ongoing declines and, while not yet formally listed, is categorised as Endangered under IUCN criteria A2(a) and B2(a)(b) based on the observed extent of population decline and distribution contraction. Evidence points toward the lethal effects of the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) as the primary driver of the species' decline, with habitat loss and climate change placing additional pressures on this threatened species.

Progress to date

In 2022, 200 tadpoles were sourced from two distinct wild populations to establish the assurance population. The program faced some initial challenges and mortality, but following revision of water management and husbandry practices, and disease treatment of metamorphs, it has successfully reared Bd-free individuals to adulthood to establish the breeding colony [3]. The program has achieved consistent and successful reproduction from early 2024, with over 42 highly fertile clutches spawned to date (as of 1 July 2026) and exceptional tadpole survivorship. Overall, the program has resulted in the reintroduction of over 8,700 first-generation (F1) tadpoles across 15 release sites within the species' historical range in New South Wales (NSW), Australia — a remarkable milestone and celebrated success, particularly given the infancy of the program.

This CBP is not only a critical step in the survival of the Southern Stuttering Frog, but also a broader effort to restore the biodiversity of their ecosystems. By returning these frogs to their native environments, we are contributing to the long-term health and resilience of these important habitats. Symbio Conservation Foundation is deeply committed to being at the forefront of conservation efforts, working tirelessly to ensure that Australia's wildlife has the best chance of survival. Through continued collaboration with expert partners and our passionate team, we are hopeful that this program will not only secure a future for the species but also set the stage for other successful recovery projects across Australia.

The Future

The CBP's primary objective is to continue to breed and release viable offspring into the Illawarra and South Coast regions of NSW. Monitoring of reintroduced populations (visual surveys and audio-recording devices) will continue, and there is already evidence of wild breeding at one release site, following a trial release in 2020 prior to the establishment of the CBP. As released offspring mature to adulthood over the coming years, we will obtain a better indication of the program's success as we collect data and observations on survival to maturity and reproduction in the wild across our reintroduction sites. Within the CBP, tadpoles from a third wild source population have been collected and are currently being reared to maturity to enter the breeding program and enhance the genetic diversity of the colony. Additionally, a research program has been initiated to investigate optimal nutrition for the species to maximise the release of wild-fit offspring.

The Team

To ensure science-based decision making for all conservation actions, conservation planning for the Southern Stuttering Frog involves expert engagement with a senior threatened species officer, conservation managers, academic researchers, and senior ecologists. We acknowledge the contributions and expert knowledge provided by the following individuals who have been integral to the success of the program to date: Jarrad Prangell, Amber Harrison, Matthew Radnidge, Garry Daly, Rachel Melrose, Chad Beranek, Aimee Silla, Phillip Byrne, Michael McFadden, Damien Esquerré, Kamryn Carter, and Michael Mahony.

Funding: The Southern Stuttering frog Conservation Breeding Program is funded by the Symbio Conservation Foundation and Symbio Wildlife Park, Australia. Initial construction of the breeding facilities were funded by the Australian Government's Bushfire Recovery Program for Wildlife and their Habitats.

References

1. Scheele, B.C., Pasmans, F., Skerratt, L.F., Berger, L., Martel, A., Beukema, W., Acevedo, A.A., Burrowes, P.A., Carvalho, T., Catenazzi, A., et al. 2019. Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science 363: 1459–1463. https://doi.org/10.1126/science.aav0379
2. Daly, G., & Craven, P. 2011. The disappearance of the Stuttering Frog Mixophyes balbus at Macquarie Pass National Park, New South Wales. Australian Zoologist 35: 846–852. https://doi.org/10.7882/AZ.2011.036
3. Harrison, A.R., Prangell, J., Radnidge, M., & Silla, A.J. 2026. Conservation breeding success of the recently described Southern Stuttering Frog, Mixophyes australis. Conservation 6(2): 63. https://www.mdpi.com/2673-7159/6/2/63
4. Mahony, M.J., Bertozzi, T., Guzinski, J., Hines, H.B., & Donnellan, S.C. 2023. A new species of barred frog, Mixophyes (Anura: Myobatrachidae) from south-eastern Australia identified by molecular genetic analyses. Zootaxa 5297(3): 301–336. https://www.biotaxa.org/Zootaxa/article/view/zootaxa.5297.3.1

Watch

The Symbio Conservation Foundation's conservation breeding programs — including the Southern Stuttering Frog, Green and Golden Bell Frog, and Bellinger River Turtle — are featured in this short film.