Tiny Tenants Favour Concrete Over Timber

In a twist that might surprise any traditional Queensland home builder, new research suggests some of the region’s smallest residents prefer concrete apartments to timber dwellings.

Scientists studying the tiny Robust Whistling Frog (Austrochaperina robusta) have discovered the elusive ground-dwelling amphibians are happily moving into specially designed artificial shelters, and even raising their families there.

The findings, published in Ecology and Evolution, reveal that hundreds of the frogs used the structures throughout their entire life cycle, from egg to adulthood.

Lead author and James Cook University PhD candidate Jordy Groffen said the shelters were created to mimic the frogs’ natural hiding spots beneath rocks and fallen logs.

“We knew they normally live under rocks and logs … so we found fallen trees on-site and chopped them into the right size,” he said.

While some shelters were made from timber, others were crafted from concrete.

“The concrete ones were made here at the University. They’re boulder-sized and have six chambers with multiple passages … like six-pack apartments. Some of them had beautiful moss growing over them.

“The frogs liked the shelters more than we expected. It’s a new non-invasive way to monitor and help frog populations”.

Over the course of the study, researchers recorded more than 800 frog observations, with one survey turning up an impressive 45 residents.

“Although they used them straight away, it still took two years before they bred in them … they had to settle in a bit. But when they did breed in them, they loved it,” Mr Groffen said.

“We found both males and females and we also found eggs in them. We had one male with three nests in a single season. That was great because we know very little about their egg stage.”

Traditionally, frog monitoring relies on listening for mating calls – a method that only detects adult males.

“Normally you only find eggs by flipping things over, which can damage the micro habitat. There’s a chance you might hurt the frogs or their eggs,” Mr Groffen said.

“These frogs are only two centimetres long and brown, living in the leaf litter. We thought that if we make something they actually enjoy, they might come to us instead.”

Tiny temperature loggers placed in the shelters also revealed why the frogs might favour their concrete digs.

“In the winter or dry season in Paluma it can still get below 10 degrees. The concrete shelters warm up bit more and stay warmer for longer, a bit like passive housing,” he said.

“Previously we didn't even know where they were in the dry season. Now we know there are more frogs under the concrete shelters in the dry season than in the hotter wet season.”

While the Robust Whistling Frog is not currently threatened, the research may offer valuable tools for protecting other vulnerable ground-dwelling species.

A Robust whistling frog tending to its eggs. Photo source: JCU / Credit J.Groffen

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