Securing a Future for the Northern Corroboree Frog

Up in the mountainous regions of south-eastern Australia, one of its most iconic and brightly-coloured inhabitants is facing the real risk of extinction within our lifetime.

The Northern Corroboree Frog (Pseudophryne pengilleyi) is a small, myobatrachid frog that occupies high elevation seepages, sphagnum bogs, wet tussock grasslands and subalpine woodlands in the mountainous regions of south-eastern Australia. The species is also culturally significant to the Traditional Owners of the high country where it occurs (1).

The species is easily recognised, with its most striking feature being its vivid patterning. The bright yellow to greenish-yellow longitudinal stripes alternate with black ones, whilst its ventral surface possesses a mixture of yellow and white spots and blotches on a black background. The intense colouration of this frog is a signal to potential predators of its toxicity. This species possesses a combination of powerful phenolic alkaloids in its skin, combining pumiliotoxins, obtained from their diet, with pseudophrynamines that have been synthesised by the frog.

Despite this, this very important species has been decimated in recent decades, with the population declining heavily since the 1980s. It is now listed under state and federal government classifications as Critically Endangered. The primary cause of their decline has been infection with amphibian chytrid fungus (Batrachochytrium dendrobatidis) (2). The species is very susceptible to the pathogen, with the fungus being well suited to its cool climate habitat. Furthermore, ongoing declines are greatly facilitated by its co-existence with the Common Eastern Froglet (Crinia signifera). The froglet acts as a reservoir host species, amplifying the presence of the fungus in the environment and offering no respite for the corroboree frog (3).

Unfortunately, this species has also suffered from additional threats. Climate change is having an increasing impact on this species, due to an increased frequency of prolonged droughts (4). As this species creates moist, terrestrial nests, often around ephemeral pools or seepages, it relies on pool inundation from rainfall or snowmelt for eggs to hatch and the tadpoles to survive to metamorphosis.

Furthermore, periods of extended drought have resulted in large bushfires, which have been demonstrated to impact on this species (5). Additional threatening processes include weed incursion and habitat disturbance by feral herbivores, including feral pigs (Sus scrofa) and feral horses (Equus caballus) (6).

Conservation breeding program

With the species declining further, conservation practitioners moved to quickly establish insurance colonies for this species. In the early 2000s, eggs were collected from throughout the range of two of the three recognised Evolutionary Significant Units (ESUs) of the species. The Northern and Southern Brindabella ESUs had each declined to less than a few hundred individuals and were at serious risk of extinction. These were initially reared at Tidbinbilla Nature Reserve, where the Southern Brindabella population remains, whilst the Northern Brindabella frogs were transferred to Taronga Conservation Society Australia (TCSA) in Sydney. In 2020, the third ESU, ironically named the Fiery Ranges ESU, was quickly established in an insurance colony at the TCSA after the megafires threatened many of the remaining populations.

This species is now held at both of these institutions, and Healesville Sanctuary, where they are kept for breeding and reintroduction to the wild. Each population is maintained in permanent quarantine to protect the species from disease risk and are serviced by experienced staff. The facilities are well insulated and are in fact refrigerated, in order for them to be maintained at 5 degrees Celsius during the winter months. Frogs are supplied with filtered water and are provided with appropriate levels of UVB lighting, with lighting controlled by a photosensitive switch, allowing them to experience natural photoperiod lengths throughout the year.

Although it took a number of years in the early stages of the program to develop husbandry and breeding protocols, these are now well established. Each year, the program produces thousands of eggs, which have enabled a number of translocation attempts, in addition to various targeted conservation research. Such research has included the development of assisted reproductive technologies (7), improved husbandry protocols (8, 9) and investigating immunity to chytrid fungus.

Translocation to secure the species in the wild

As this species has declined or disappeared from significant parts of its range, there is now a focus to reintroduce populations or to augment existing populations. Translocations have been taking place in the Northern and Southern Brindabella populations for over a decade (10). In the Northern Brindabella population, various trials have been undertaken, including the release of different life stages and in different seasons. Overall, releases into this ESU from the TCSA alone have totalled over 2500 eggs and almost 2000 frogs.

Translocation efforts have begun to ramp up in recent years, with 1500 of the above-mentioned frogs released into Brindabella National Park in the last three years alone. Each year, monitoring of calling males on their nests allows the team to identify the individual frog based on their pattern. Photos of the dorsal and ventral surface are taken of each individual frog released, with the males on nests during surveys able to be matched back to their release photos from their unique pattern, much like a fingerprint in humans.

The conservation program to secure this species is a dynamic and evolving effort, adapting each year to new knowledge and technologies. It is a large collaboration between many organisations, including state wildlife agencies (NSW Department of Climate Change, Energy, the Environment and Water and the ACT Government), zoos (the TCSA, Tidbinbilla Nature Reserve and Healesville Sanctuary), universities (University of Wollongong and University of Melbourne) and many others. More recently, this program has established a close relationship with the Wolgalu/Wiradjuri Community of Brungle/Tumut, who are the Traditional Owners of much of the Country where the species occurs. All aspects of fieldwork and management for this species in Kosciuszko National Park and adjacent state forest areas are now undertaken in partnership with the Bugang Bila Indigenous Ranger Program.

References

1. Connolly, D., Williams, A., and Williams, S. (2017). Recognition of the cultural significance of water to the Wolgalu Aboriginal nation in the upper Murrumbidgee River catchment. Snowy Flow Response Modelling and Modelling program, NSW DPI Water, Sydney.
2. Scheele, B. C., Skerratt, L. F., Grogan, L. F., Hunter, D. A., Clemann, N., McFadden, M., ... & Berger, L. (2017). After the epidemic: ongoing declines, stabilizations and recoveries in amphibians afflicted by chytridiomycosis. Biological Conservation, 206, 37-46. https://doi.org/10.1016/j.biocon.2016.12.010
3. Scheele, B. C., Hunter, D. A., Brannelly, L. A., Skerratt, L. F., & Driscoll, D. A. (2017). Reservoir-host amplification of disease impact in an endangered amphibian. Conservation Biology, 31(3), 592-600. https://doi.org/10.1111/cobi.12830
4. Scheele, B. C., Driscoll, D. A., Fischer, J., & Hunter, D. A. (2012). Decline of an endangered amphibian during an extreme climatic event. Ecosphere, 3(11), 1-15. https://doi.org/10.1890/ES12-00108.1
5. Mahony, M. J., Hines, H. B., Lemckert, F., Newell, D., Roberts, J. D., Rowley, J. J., ... & West, M. (2023). The impacts of the 2019–20 wildfires on Australian frogs, in Rumpff, L., Legge, S. M., van Leeuwen, S., Wintle, B. A. & Woinarski, J. C. Z. (eds.) Australia’s Megafires: Biodiversity Impacts and Lessons from 2019-2020. CSIRO Publishing, Clayton, Victoria. Pp 167-181. https://doi.org/10.1071/9781486316656.BK08085_ch13
6. Foster, C. N., & Scheele, B. C. (2019). Feral-horse impacts on corroboree frog habitat in the Australian Alps. Wildlife Research, 46(2), 184-190. https://doi.org/10.1071/WR18093
7. Silla, A. J., McFadden, M., & Byrne, P. G. (2018). Hormone-induced spawning of the critically endangered northern corroboree frog Pseudophryne pengilleyi. Reproduction, Fertility and Development, 30(10), 1352-1358. https://doi.org/10.1071/RD18011
8. McFadden, M. S., Silla, A. J., Kelleher, S. R., & Byrne, P. G. (2025). Effects of ultraviolet radiation on the activity, survival, and growth of the critically endangered northern corroboree frog. Biology Open, 14(5), bio061827. https://doi.org/10.1242/bio.061827
9. McFadden, M. S., Silla, A. J., Kelleher, S. R., Endler, J. A., Landler, L., & Byrne, P. G. (2025). Optimising conservation breeding efforts: Investigating the effects of ultraviolet radiation on colouration of the northern corroboree frog (Pseudophryne pengilleyi). Frontiers in Amphibian and Reptile Science, 3, 1669704. https://doi.org/10.3389/famrs.2025.1669704
10. McFadden, M., D. Hunter, Evans, M., B. Scheele., R. Pietsch and P. Harlow (2016). Reintroduction of the Northern Corroboree Frog into the Northern Brindabella mountains, New South Wales, Australia, in Soorae, P. S. (ed.) Global Re-introduction Perspectives: 2015. IUCN/SSC Re-introduction Specialist Group, Abu Dhabi, UAE. Pp 35-39.