Mating Calls of Frogs Expose Them to Predator Bats [VIDEO]

Serenading females can prove dangerous for tungara male frogs as the water ripples they create attract predators.

Researchers at the University of Texas, Austin and the Smithsonian Tropical Research Institute (STRI) reveal that when a male tungara frog, native to Central and South America, makes mating calls from shallow pools, the ripples produced in the water exposes it foes like bats.

As the male tungara frog (Physalaemus pustulosus) produces mating calls, the vocal sac inflates and deflates similar to a pulsing balloon. The calls are based on a pattern of 'whines' and 'chucks'. The frog's call is multisensory.

The moment the frogs sense a bat fluttering above them, they clam up immediately, but unfortunately, the ripples continue for several seconds after the calls end. The bats use echolocation to detect the ripples and feast on the frog.

"The interesting thing is that these frogs have evolved a strategy to escape predation," said lead author Wouter Halfwerk, a postdoctoral researcher at UT. "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."

"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, professor in the Department of Integrative Biology at UT Austin, said in statement. "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."

One interesting pattern they noticed in the frog-eating bats (Trachops cirrhosus) was that these bats were more likely to attack those frogs that produced both mating calls as well as ripples. They did not attack the frogs with mating calls but  no ripples, clearly indicating that bats are highly dependent on ripples to detect their prey, i.e echolocation. But the frogs that produce ripples get lucky if the surrounding area is covered with leaf litter, making it harder for the bats to detect the ripples.

If the mating calls along with ripples are produced outside the male territory of defense, a circle of 15 cm across, the rival males' respond with a call twice as fast than to a call itself sans ripples. But if the call and ripples were within the territory of defense, the rival frogs called less.

The findings were documented in the journal Science.