Saving the Corroboree

Scientists have discovered that the secret to the survival of critically endangered northern corroboree frogs may be a short, sharp winter.

Story By Ken Eastwood

Researchers at Tidbinbilla Nature Reserve in the Australian Capital Territory have become the first to breed the critically endangered northern corroboree frog in captivity. In the wilds of the ACT, there are believed to be less than 100 of the beautiful black and yellow (or lime) striped frog remaining.
But at Tidbinbilla, a wildlife-rich 6500-hectare nature reserve south of Canberra, there are now nearly 2000 corroboree frogs crawling and swimming in terrariums in three climate-controlled shipping containers. According to Murray Evans, senior wildlife ecologist for the ACT Parks, Conservation and Lands Department, the key to getting the frogs to breed has been giving them a six-week winter period of about five degrees Celsius, then over the next week bringing them sharply into a warmer environment of about 20 degrees Celsius. “We think it’s like a slap in the face to their hormone system,” he says. “No one had been able to breed them, but we managed to breed them two years ago, and last year again we had a good result with 900–1000 eggs.”
During the enforced 'winter' the frogs are crowded into small containers of damp sphagnum moss and are given no food. “They hunker down and just wait it out,” Murray says. “They just become inactive.”
Then after the change to 'summer' conditions, the frogs are released into larger terrariums of nearly a metre square, with access to 13 other randomly picked frogs, and given lashings of crickets.
Until the mid-1990s, all of the corroboree frogs were considered one species. Then genetic work showed that the northern variety (which is usually more lime than yellow) and the southern variety are quite different. All are critically endangered.
The other institutions breeding corroboree frogs – such as Taronga Zoo in Sydney, Melbourne Zoo, Healesville Sanctuary and the Amphibian Research Centre in Melbourne – have the southern variety, but have not had anywhere near the breeding success of Tidbinbilla. “It’s always possible it’s the species not the regime,” Murray says. “But we knew what the other institutions were doing with southerns wasn’t working, so we just thought we’d do something different.” Murray says about 20 percent of the sexually active females are now breeding, compared to about one percent in the other institutions.