The red-eyed tree frog’s secret is out: rather than croaking an attractive tune, it uses vibrations to improve its chances of finding a mate.

Flinders senior lecturer and conservation biologist with Zoos SA Dr Gregory Johnston and colleagues from Boston University in the USA have discovered that the flamboyantly coloured red-eyed tree frog from Central America uses its rear legs to send ‘seismic signals’ along tree branches to ward off rival males encroaching on its territory.

The discovery, presented in the journal Current Biology, paves the way for “a whole realm of possibilities” of new research into how animals communicate.

“Unlike most species of frogs, the red-eyed tree frog doesn’t show any evidence of females choosing a mate with the loudest or prettiest voice,” Dr Johnston said.

“Instead, male red-eyed tree frogs set up territories around the edge of a pond and sequester females and mate with them. Females are quite indiscriminate and will mate with several males,” he said.

“Having a territory is really important to these male frogs for getting a mate and reproducing. By creating a vibration on a bush, they send a clear signal to other males to ‘back off’ while keeping it a secret from predators, which cannot detect the vibrations.

“You end up with these frogs very evenly spaced, one frog per small bush. It’s about negotiating space.”

Dr Johnston made the discovery while observing the frogs in a Panamanian rainforest in 1999 while working with the Smithsonian Tropical Research Institute.

“I saw the frogs making little tantrums at each other and from my PhD research into territorial lizards I recognised it as territorial behaviour,” he said.

His initial investigation, using a miniature seismograph to measure the signals, led to experiments over more than seven years by his North American colleagues.

It is the first time the use of vibration as a method of communicating has been demonstrated in a tree-dwelling vertebrate.

Dr Johnston will be teaching in the new Bachelor of Science (Animal Behaviour) degree to be offered at Flinders from 2011.