Endangered giant burrowing frog returns to wild after tadpoles rescued from ashes of black summer fires

After the 2019-20 black summer bushfires, scientists in eastern Victoria stumbled across something they had been after for years: puddles of tadpoles from the southern giant burrowing frog, one of the state’s most cryptic amphibians.The fires had torn through extensive areas in East Gippsland, sparking concerns for the survival of the frog, which is considered critically endangered in Victoria.About 160 tadpoles were collected and transported to Melbourne zoo, where they were raised through to metamorphosis into frogs and successfully bred in captivity for the first time last year.In a homecoming more than half a decade in the making, 53 of the original tadpoles – now male frogs about five years old – have been returned to their native habitat in a remote area of the state’s east.The elusive frogs grow to roughly the size of a cricket ball in adulthood, and are believed to have long lifespans. Matt Clancy, a herpetologist at Snowline Ecology and an expert in the species, said that like other large frog species such as green tree frogs, giant burrowing frogs “could quite easily get over 20 years old”.“Being such a large frog, you think they’d be easy to find, but they spend a lot of time buried underground in … sandy soils and forested environments.“They will hunker down and not move at all until the next rains come and they emerge,” he said.The frogs surface to breed in ephemeral creeks and ponds only when conditions are right. Tadpoles can take three months to two years to metamorphose, usually emerging as juvenile frogs in spring or summer, Clancy said.Southern giant burrowing frog returned to their native habitatThe 53 frogs were released immediately after big thunderstorms over the past several weeks at sites that had received 80 to 100mm of rain, he said.Some of the released adults were not suitable for a captive breeding program run by Zoos Victoria. Ryan Moes, specialist amphibian keeper at Zoos Victoria, said the team conducted genetic testing on all the tadpoles originally collected.“Within a breeding program, you don’t want to have all siblings breeding together,” he said. “The best thing to do was just to raise those frogs up and release them back out … into the wild once they were healthy frogs.”Each frog was tagged before release, and song meters have been installed at release sites to detect the frogs’ calls.Moes said the breeding program, which may involve future tadpole collections, ultimately aimed to ensure “those wild populations stay healthy and robust, and that the frog doesn’t go extinct”.Giant burrowing frogs were split into two distinct subspecies – northern and southern – in 2021. Populations have been severely affected by habitat destruction and extreme climate events.More frequent and severe bushfires and droughts due to climate change, as well as less rainfall, were ongoing existential threats, Moes said.There are only five known breeding sites of southern giant burrowing frog in Victoria.