Something to whistle about: Two “whistling” frogs in South Australia new to science

A taxonomic assessment of the Brown Tree Frog reveals two additional undescribed species in South Australia, including a species endemic to Kangaroo Island.

The Brown Tree Frog (Litoria ewingii) is a medium-sized (up to 4.5 cm) and common south-eastern Australian frog species, known for its characteristic whistle-like call. The species is widespread but has a fragmented distribution which spans more than 350,000 km² across southern New South Wales, Victoria, Tasmania and southern South Australia.

The Brown Tree Frog lives in a range of habitats and is often found in urban areas, such as backyards and suburban parklands. They can be found from sea level to 1,200 metres elevation and an introduced population even thrives in the comparatively cooler conditions of New Zealand.

In our new paper, we re-assessed the systematics and taxonomy of the Brown Tree Frog and sought to understand how biogeographic processes have shaped their evolution in south-eastern Australia. Using comparisons of their DNA, body shape and mating calls submitted by participants of the Australian Museum’s FrogID project, we found that the Brown Tree Frog is not a single species, but a composite of three geographically isolated species. Amazingly, the species appear to have evolved from their common ancestor around 2 to 3 million years ago and they have been isolated across major biogeographic barriers since at least the end of the last Ice Age.

In the study, we scientifically describe two of the species, both from South Australia, including the South Australian Tree Frog (Litoria calliscelis), which is found in the Mount Lofty Ranges, Fleurieu Peninsula and Adelaide coastal plain, and the Kangaroo Island Tree Frog (Litoria sibilus), which is restricted to Kangaroo Island.

Luckily, the Brown Tree Frog and South Australian Tree Frog appear to be relatively abundant throughout their large ranges. However, the Kangaroo Island Tree Frog is likely to be of high conservation concern, given its restricted distribution (<4,405 km2) and the potential threat posed by the 2019–20 Kangaroo Island bushfires, which were the largest in the island’s recorded history. Now we know how range-restricted the Kangaroo Island Tree Frog is, we can prioritise further research to better understand what threats it faces and determine if conservation management is required to ensure its long-term survival.

This study, along with many other recent species discoveries, highlights that much is still left to be learned about Australia’s biodiversity, even for our most common backyard frogs and the important role that members of the public can play in these discoveries!

Tom Parkin, Research Assistant, Herpetology, Australian Museum.

Dr Jodi Rowley, Curator, Amphibian and Reptile Conservation Biology, Australian Museum.

Professor Stephen Donnellan, Honorary Researcher, South Australian Museum.