Bats that are craving frog for dinner look at the ripples formed by the amphibians' love songs.
Túngara frogs usually stop calling if they see a hungry bat flying overhead, but the ripples can still be spotted for a few seconds, a University of Texas at Austin news release reported.
Bats use echolocation to locate these ripples so that they can snatch up the prey. The frogs emit a pattern of "whines" and "chucks" that can be detected by both potential mate and predator.
During the frog's mating call the vocal sac inflates and deflates "like a pulsing balloon," this movement is what creates the ripples on the water's surface.
"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," Mike Ryan, co-author on the study and professor in the Department of Integrative Biology at UT Austin, said in the news 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 team observed that predatory bats were significantly more likely to attack a frog when there was both a frog call and a ripple than a call alone. They also noticed bats are less likely to notice the ripples if there is clutter surrounding the prey (such as leaves).
"The interesting thing is that these frogs have evolved a strategy to escape predation," lead author Wouter Halfwerk, a postdoctoral researcher at UT Austin who is also affiliated with STRI and Leiden University, said in the news 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."
