Northern corroboree frog
Corroboree Frogs have a restricted distribution to high altitude areas, where they breed in waterlogged areas such as sphagnum moss bogs during summer, and spend winter in the surrounding woodland. There are two closely related species of Corroboree Frog:
- Northern Corroboree Frogs (Pseudophryne pengilleyi) occur in the Brindabella and Bimberi Ranges in the ACT and nearby areas of NSW;
- Southern Corroboree Frogs (Pseudophryne corroboree) occur in the Snowy Mountains of NSW.
Adult Corroboree Frogs are only two to three centimetres long, have distinctive black, yellow and white markings on their backs, and are recognised by their short ‘squelch’ calls.
Both species of Corroboree Frog suffered severe declines in numbers during the 1980s and numbers continue to dwindle. Both species are listed as threatened nationally and in each State/Territory where they occur. There is a worldwide decline in frog numbers believed to be due largely to disease caused by the introduced Chytrid fungus. Drought may have also exacerbated the situation for Corroboree Frogs.
Between January and early March, females lay approximately 25 eggs, a small number compared to most frog species. In contrast, Cane Toads (Bufo marinus) can lay around 20,000 eggs. The eggs are laid out of water in sphagnum moss or other damp vegetation next to a pool. The eggs develop slowly over autumn to an advanced tadpole stage, which then hatch when pool levels rise from heavy rain or melted snow and flood the nest. After several weeks of feeding and growing in the cool clear pools, the tadpoles metamorphose into juvenile frogs during spring or summer.
There are estimated to be less than 50 Northern Corroboree Frogs remaining in the wild in the ACT. Most of the ACT’s Northern Corroboree Frog habitats were severely burnt in the 2003 bushfires, though these areas are recovering well and the few remaining Corroboree Frogs are using these areas to breed.
As part of a recovery program for the Northern Corroboree Frog, ecologists in Territory and Municipal Services (TAMS) collected eggs from the wild and established a captive assurance population in a biosecure facility at Tidbinbilla Nature Reserve. The facility at Tidbinbilla is designed to keep the captive Corroboree Frog population free of infection from the deadly Chytrid fungus, that has devastated wild populations of Corroboree Frog. The aim of the program is to eventually breed and release Corroboree Frogs back into the wild to bolster wild populations.
Attempts by a number of zoos to breed the related Southern Corroboree Frog have been largely unsuccessful, highlighting the challenge of recreating the specialised breeding conditions for these frogs in captivity. After waiting four years for the frogs to reach breeding age, ecologists and wildlife officers in TAMS successfully recreated the necessary conditions for the successful breeding of Northern Corroboree Frogs in 2008. Successful breeding has also occurred in each subsequent year since. In 2010, Taronga Zoo adopted the technique used at Tidbinbilla and successfully bred the related Southern Corroboree Frog.Breeding and raising Corroboree Frogs in captivity, where conditions can be controlled, results in a far higher survivorship rate than in the wild. Apart from Chytrid fungus, one of the greatest sources of mortality in wild populations is variable or low rainfall. Insufficient rainfall or snow can result in eggs not hatching (because pools don’t flood the nests) or pools drying before tadpoles can metamorphose. There are currently over 1,000 Northern Corroboree Frogs in the captive population at Tidbinbilla, which is many times more than exist in the wild in the ACT (estimated to be less than 50 individuals).