Save our frogs

Urban frogs are in decline. LEONARD CRONIN looks at what has gone wrong, and what we can do as gardeners to help

We will remember this year as the year of the green tree frog. Our house was inundated over summer with large green tree frogs living in our bathroom, poking their heads out of the sink overflow, clinging to the toilet bowl, serenading us at night – their amplified calls reverberating from the downpipes. We’ve had a wet year and, after the droughts and bushfires, our local tree frog population has boomed.

Other frogs haven’t done so well. Frogs are one of the planet’s most threatened animal groups, with around 40 per cent threatened with extinction. Australia has some of the world’s most amazing frogs, and we need to seriously review our conservation strategies to prevent even more joining the list of vanished species.

Take the gastric-brooding frog, whose females swallow their fertilised eggs and brood the tadpoles in their stomach, giving birth to tiny froglets through their mouth. This remarkable frog was discovered in 1972 in the streams of the Conondale Ranges north of Brisbane, but a decade later it had vanished and, together with its northern relative and four other highland rainforest frogs, is now presumed extinct. The list of critically endangered Australian frogs has now grown to 15 species, with another nine on the endangered list.

frogs under threat

One of the greatest threats to Australia’s frogs, and amphibians around the world, is chytrid fungus, which is thought to have originated in Africa and spread around the world by the export of the African clawed frog (Xenopus laevis). In the 1930s, it was discovered that this frog would reliably lay eggs when injected with the urine of pregnant women. This revolutionised pregnancy testing, but the tens of thousands of frogs sent overseas between the 1940s and 1960s carried the fungus with them.

Chytrid fungus has wiped out as many as 200 frog species around the world since the 1970s, and pushed many more to the brink of extinction. It is mostly limited to moist and cooler environments, such as rainforests, and has devastated local frog populations across Australia’s entire east coast and tablelands, including species that were once widespread and common.

The fungus infects the skin cells of frogs and uses the frogs’ natural process of skin shedding to release fungal spores into the water, where they infect other frogs. While there’s no known cure for this apocalyptic fungal disease, Australian scientists have discovered that endangered frogs have a far greater survival rate when translocated to habitats where small amounts of salt have been added to the water.

Peron’s tree frog; green tree frog.