In behavior never before recorded by scientists, male red-eyed tree frogs are shown shaking their rumps and entire bodies to show dominance. The shaking often precedes wrestling between the two males.

© 2010 National Geographic; video: Michael S. Caldwell

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Unedited Transcript

No, they’re not shivering. And no, they’re not getting shocked. These red-eyed tree frogs in Panama have been recorded shaking their behinds to send a message.

This shaking, known as tremulation, is a form of communication between male tree frogs.

The males are tremulating to establish which is the dominant male. They’re claiming territory for their ‘calling area’ where they spend the night calling for a female mate.

Sometimes, the shaking leads to wrestling among males… and maybe even more shaking, until the loser retreats.

Researcher Michael Caldwell of Boston University and his colleagues used infrared cameras at the Smithsonian Tropical Research Institute in Panama to record the tremulation. They even used robo-frogs, seen in the lower right here, for part of the experiment.

Caldwell suggests the shaking behavior had not been previously observed, probably because the tree frogs behave differently under white light, which researchers usually use to record these nocturnal creatures.

The red-eyed tree frogs live in the rain forests from southern Mexico to Northern South America.

Many scientists believe it developed its vivid scarlet eyes to shock predators into at least briefly questioning their meal choice.

And their neon-green bodies coupled with the red eyes may play havoc with their nocturnal predators’ visual senses.

The tree frogs sleep by day stuck to leaf-bottoms with their eyes closed and body markings covered.

The scientists believe the vibrations created by the shaking are in important part of the communication because in many instances, the shaking frog was not even in view of the intended recipient of the message. And even if he had his back turned, it seemed the receiving frog knew what the message was.

Caldwell and his colleagues published their findings in a recent online issue of “Current Biology.”

Though their discoveries are believed to be new, the researchers don’t think the shaking behavior is isolated to the red-eyed tree frogs. They suggest that vibrational signaling might, in fact, be common in other vertebrates that spend most of their time in the foliage of the rain forests.