New robot frog gets into fights

Finally: A robot that provokes male frogs enough to start a brawl.

That engineering triumph brings hope to Peter M. Narins of the University of California, Los Angeles. He and his colleagues have been trying to decode the communications of the brilliant-thighed dart-poison frog, Epipedobates femoralis, but they couldn’t get the frogs to finish an interaction.

Males of this tiny tropical species stake out territories on the forest floor. Within their domains, males climb atop a log or other object and belt out calls. When Narins recorded the calls and played them back, males readily hopped toward the sound. That’s where the experiment stalled. Males approached but didn’t attack.

Narins and his collaborators may have solved the problem by building what they call Roborana. (Rana means frog in Latin.) This fake frog sits on what looks like a plain old log. However, the log houses a speaker and an air pump. From a hiding place, the researchers trigger broadcasts of a male’s call. The air pump inflates and deflates Roborana’s throat sac, made from a condom, in sync with the calls.

Adding the model with this sac makes a huge difference, Narins reports.

Simply broadcasting the call has the usual effect of luring a male, but the puffing sac provokes attacks. He and his colleagues have videotaped a frog hopping over to Roborana, pouncing on top of the robot, and swiping at the vocal sac. With this new tool, Narins hopes to tease out more about how frogs interpret these signals.