When it comes to communication, Brazilian torrent frogs just can't sit still.
The amphibians not only use noisy vocal signals, like peeps and squeaks, to talk to each other, they also wave their arms and legs, tap their toes, bob their heads, and puff up their vocal sacs for show.
Researchers observed these frogs, scientifically known as Hylodes japi, performing one of the most complex communication systems known in frogs, as reported in a paper published Wednesday in the journal PLOS ONE.
If you've ever been near a frog-filled swamp on a warm summer night, you know just how noisy the hoppers can be. But Brazilian torrent frogs dwell in and around streams that aren't just trickling. These streams are noisy torrents of water (which give the frog its name), so they may have some competition for the airwaves.
That probably explains the antics of the territorial males of this frog species. When he wants to woo a female or tell another male to back off, a male Brazilian torrent frog has to make more than a vocal exclamation.
Sometimes the frogs would puff up their vocal sacs without uttering a call. These vocal sacs are a bright whitish hue, so puffing them out would flash another frog a clear signal.
The researchers found that the frogs could puff up either one of their two vocal sacs independently, and would usually choose the one closest to an intruder or potential mate.
Other displays included complex leg or arm movements. The scientists observed the frogs lifting a leg, waving an arm and even trembling their toes in a wave-like pattern.
These frogs might also raise or lower their bodies, or otherwise change their posture. Occasionally, the frogs would even bob just their head up or down in a jerky movement.
These stream-dwelling frogs may have even made up the new dance craze: head snaking.
When a male wants to woo a mate, he quickly edges near her. Face-to-face, the male frog swings his head from side to side while raising and lowering it. The motion ends up taking a sort of snakelike path. This shows off the male's cream-colored throat and chest to the object of his affection.
All these intricate motions are in addition to complex vocal signals including peeps, squeals, and courtship calls. The combination of different modes of communication is a novelty in frogs, study lead author Fábio de Sá tells The Christian Science Monitor in an email.
Although the males are largely the ones performing these strange froggy calls and motions, the females get in on it in a unique way too.
During courtship, females wave their arms and legs a bit too, but the surprise came in the way they interact directly with a male.
"Previously unknown in frogs," the study authors write in their paper, "we also describe a bimodal inter-sexual communication system where the female stimulates the male to emit a courtship call."
If a female is interested in a male, she can actually stimulate his courtship calls and displays. By wiggling her limbs in specific ways and resting part of her throat on top of the male, she tells him she accepts his courtship. He will continue showing off for her with his dynamic song and dance.
Uncovering the diverse capabilities of frogs helps us "understand the world where we live," de Sá says. "We get surprised in how complex organisms can be."