De Sá and his team made the recordings in the biological reserve of Serra do Japi in the state of Sao Paulo, southeastern Brazil. The forested region provides important habitat for many species of plants and animals.
The researchers documented the calls as well as the visual displays of the frogs. The latter consisted of toe trembling, toe flagging (which reveals the frog's silver-white underside), foot shaking, hand shaking, arm waving, head bobbing, full body jerks, and much more.
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A particularly complex move is the "head snake." Males seem to use this to mesmerize females. While approaching prospective mates, the males will move their heads from side to side as snakes do when in front of a snake charmer. The males do this looking right into the eyes of the desired female and at very close range, but not touching her.
Actual courtship is quite a scene. While peeping and squealing, the males tremble their toes, engage in toe flagging, foot shaking, hand shaking, arm lifting, head bobbing, body jerking and perform throat displays. While all of this is going on, the females remain motionless. Only later, with a subtle lift of an arm as if to say, "Yoo hoo, I'm ready," does a female often signal her willingness to mate. She then rubs part of her body on the male's back, with her hands gently touching him. Intercourse usually starts thereafter.
The scientists also observed that females could stimulate males to emit courtship calls with just a lift of their arm, most often the left one. Such control has never been documented before in frogs.
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Another novelty: the researchers found that males could choose which of their two vocal sacs could be blown up, like a balloon, and used for visual displays. Each sac, arm and limb seems to be tied to unique meanings, giving the communication system tremendous flexibility and depth.