To test if the frogs actually communicated with their ultrasonic sounds, Feng and colleagues returned to China with their recording equipment and a special device that allowed playback of recorded frog calls in the audible or ultrasonic ranges. They observed eight male frogs under three experimental conditions (no sounds, playback of calls containing only audible parts and playback of just ultrasonic frog calls).
During playback, the researchers watched for evoked calling activity in which a male frog begins calling upon hearing calls from other frogs in the area. Six frogs responded to ultrasonic and audible sound ranges, with four responding with calls in both ranges. One frog called 18 times to ultrasonic calls, including four very telling rapid responses, Feng said. Another frog did not respond to ultrasonic stimulation but produced calls 18 times to an audible prompt.
Clearly, Feng said, some of the frogs indeed communicated ultrasonically. They have the ability to do so, but for some reason some frogs do and some don't, he said. "We believe that all of them have the capacity to respond to the ultrasound."
Ultrasonic communication likely will be found in other amphibians and birds, Feng said, but, until now, no one has bothered to look into it.
"Humans have always been fascinated by how some animals can discern their world through a sensing system vastly different from our own," Feng said. "The electromagnetic sense in fishes and homing pigeons, polarized light vision in ants, chemical sensing of pheromones in insects and rodents, echolocation by ultrasound in bats and dolphins, are just a few examples.
"That frogs can communicate w
Source:University of Illinois at Urbana-Champaign