The Watson's Tree Frog (Rawlinsonia watsoni) has been teetering on the edge of extinction in Victoria, but a new recovery program is hoped to turn this situation around.
The species had not been seen for 19 years and was feared extinct before it was rediscovered during an arboreal mammal and owl survey in 2015 (1). Thousands of surveys have since been conducted across historic known sites and at hundreds of new sites with predicted highly suitable habitat. By 2018/19, the species was known from more than 40 sites; however, over 80 per cent of these were subsequently burnt during Australia's devastating 2019–20 Black Summer bushfires. Watson's Tree Frogs have been increasingly difficult to find since the fire event.
The survey team, from Wild Research Pty Ltd, the Arthur Rylah Institute, Wildlife Unlimited, Zoos Victoria, Parks Victoria, and the Victorian Department of Energy, Environment and Climate Action, has tested and developed a range of methods to find the species. These include visual encounter surveys, call playbacks, eDNA surveys, passive acoustic recorder surveys, and even a trial using detection dogs. Varying approaches have been needed to address the challenge of finding this cryptic species in the often-dense forest habitats it occupies. Call playback surveys and passive acoustic recorders have proven particularly useful in locating the frog, which has a unique deep, slow, whistle-like call.
Despite all this effort, the team became increasingly concerned about the species' risk of extinction. By 2023, Watson's Tree Frogs were known at only around 10 sites, most no bigger than a child's swimming pool. To make matters worse, the frogs were known to be breeding at only six of these. Unsurprisingly, genetic studies have corroborated low diversity and small effective population size (2). A range of threats are considered to have driven the declines, including habitat disturbance from forestry activities, chytridiomycosis, introduced deer and pig activity, and intense, widespread bushfire events. Further work is required to determine how best to protect the species from these threats.
The team has taken emergency action, collecting tadpoles from breeding sites for a new conservation breeding program. In February 2023, the wild-caught tadpoles were first quarantined to clear chytrid infections and then transferred to purpose-built enclosures in Melbourne Zoo's Amphibian Bushfire Recovery Centre. Zoos Victoria built two centres, with six bio-secure and climate-controlled rooms, to care for frogs in the aftermath of the bushfires, with funding assistance from the Australian Government's Wildlife and Habitat Bushfire Recovery Program.
Melbourne Zoo's team rapidly developed a husbandry program to rear the tadpoles and a breeding recipe for the frogs. Almost 95 per cent of tadpoles survived and began to metamorphose in March 2023. The frogs reached maturity within 18 months, with the first captive breeding event occurring in July 2025.
The Zoo team, supported by Wild Research, produced almost 1,500 tadpoles in the first breeding year. The team began releasing tadpoles in November 2025 and juvenile frogs in March 2026. So far, almost 1,200 tadpoles and 200 frogs have been released to 30 new wild sites. These releases are hoped to increase the number of wild sites by 300 per cent, from 10 to 40. Other captive-bred individuals have been held back to contribute to the conservation breeding program, while others will be released at a more advanced (adult) life stage to help boost the wild population. The team will track the survival of released animals at the tadpole, juvenile, and adult life stages to inform ongoing recovery efforts.
Ultimately, the recovery of Watson's Tree Frog will depend on sustaining this momentum and translating early successes into long-term population resilience. While the conservation breeding and release program represents a critical turning point, it must be coupled with continued monitoring, targeted threat mitigation, and adaptive management across the species' range. Ongoing funding and strengthening collaborations among researchers, government, conservation practitioners, and the broader community will be essential to refine recovery actions and respond to emerging challenges. With coordinated, evidence-based efforts, there is now a genuine opportunity not only to prevent extinction, but to rebuild secure, self-sustaining populations of this iconic species in the wild.
Acknowledgments
We are grateful to teams from the Arthur Rylah Institute for Wildlife Research, Wildlife Unlimited, Moogji, Parks Victoria, and the Victorian Department of Energy, Environment and Climate Action. The efforts of Rena Gaborov, Louise Durkin, Lauren White, Carlos Pacioni, Claire McCall, Glen Johnson, Joseph Leman, Deon Gilbert, Ebony Gatto, Ryan Moes and Tom Fair have been particularly important to the project's success. Funding for this project has been provided by the Victorian Government Nature Fund program, Zoos Victoria, the Australian Government, and WIRES NSW.
References
- Gillespie, G. R., McNabb, E. & Gaborov, R. (2016). The biology and status of the large brown tree frog Litoria littlejohni in Victoria. Victorian Naturalist 133, 128–138.
- Durkin, L., White, L., Stock, S., Pacioni, C. & West, M. (2023). Adequacy of timber harvesting exclusion zones for Watson's Tree Frog. Unpublished report for the Policy and Planning Division, Bushfire and Forest Services, DEECA. Arthur Rylah Institute for Environmental Research, Department of Energy, Environment and Climate Action, Heidelberg, Victoria.