Frogs' Mating Call Cause Ripples That Attract Preying Bats

When a male túngara frog croaks, he thinks he is signaling for a mate, but new research suggests he is also alerting frog-eating bats to his very location.

According to LiveScience, researchers believe the mating croak creates ripples that bats can sense and use to locate the frog. The frogs can stop themselves and keep quiet when they sense danger, but the reverberating ripples cannot be retracted once a croak occurs.

"Animals have all kinds of sensory systems that they can use in very different ways, and they can combine their senses," study lead author Wouter Halfwerk, a postdoctoral researcher at the University of Texas, told LiveScience.

Published in the journal Science, the study found that the water ripples from the mating call continue for several seconds after the frog stops making it, allowing to bat to locate its prey.

"A general theme of this research is that the way we communicate with any kind of a signal is by creating a disturbance in the environment," study co-author Mike Ryan, an integrative biology professor at UT, said in a press release. "When we vocalize, we're causing changes in the air pressure around us and that's what our ears hear. When we use visual signals, light bounces off whatever pigments we're using and is transmitted to the receiver. Anything we do disturbs the environment, whether it's intended as a communication signal or not."

The researchers found that bats relied on the ripples to locate the frogs, due to their natural sonar sense. They could not locate their food based on the call alone when separated from the ripples. They also found that a call with ripples was more likely to generate responses, which tended to be returned with more enthusiasm.

"The interesting thing is that these frogs have evolved a strategy to escape predation," Halfwerk said in the release. "When a frog detects the shadow of a bat overhead, his first defense is to stop calling immediately. Unfortunately for the frog, the water ripples created by his call do not also stop immediately. The ripples continue to emanate out for several seconds, creating a watery bull's-eye on the frog. Bats use the ripples, thereby beating the anti-predator strategy."