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Nature's death knell: This frog's love song is a bat's dinner bell

Ripples on the water made by the tungara frog's mating call are a dead giveaway for preying bats.
Ripples on the water made by the tungara frog's mating call are a dead giveaway for preying bats.Ryan Taylor/Salisbury University

Sometimes love hurts — a lot. Just ask the tungara frog, a tiny native of Central and South America. 

The loud, low mating call made by male tungara frogs in search of a love connection has a deadly unintended effect — attracting frog-eating bats.

While the male tungara frog's love song entices the female of the species, it also creates small ripples on the ponds and puddles where the frogs gather. That helps hungry bats using a form of sonar zero in on them to snag a juicy meal, scientists reported on Thursday. 

The research, conducted in Panama and published in the journal Science, sheds new light on the evolutionary arms race that has unfolded for eons between frogs and bats — one of the most interesting fights in the animal kingdom. 

"Imagine the frog that's in a pond," behavioral biologist Wouter Halfwerk said in a telephone interview. "It's like it's being spied upon by some agent that is spying on your communications." 

"You try and make your love song and all of a sudden, yeah, you're screwed because someone is listening in on your call by using a completely different communication channel," said Halfwerk, one of the scientists in the study at the Smithsonian Tropical Research Institute in Panama. 

The brownish frogs, measuring less than an inch (2 cm) long, begin their mating calls when the sun sets in the rainforest. As the males make their calls, their vocal sacs inflate and deflate like a pulsing balloon, creating ripples on the water's surface. 

The researchers conducted experiments to show that the frog's natural predator, the fringe-lipped bat, was attracted by the mating calls but also apparently employed echolocation — the use of sound waves and echoes to determine something's location — on the ripples to find the unfortunate amphibian. 

The propagating ripples served as a watery bull's-eye, said Halfwerk, who is affiliated with Leiden University in the Netherlands and the University of Texas, Austin. 

"When a bat flies by, the frog's first line of defense is to stop calling," Rachel Page, a scientist with the Smithsonian Tropical Research Institute, said in a statement. "But the water ripples continue for another few seconds, effectively leaving a detection footprint for the approaching bat." 

With one quick swoop by the bat, the male frog ended up without a mate — and without his life. 

Nearly all the bats in the study preferred to attack frogs on ponds where the ripples were produced, compared to ponds where scientists made sure there were no such ripples. 

The bats seemed to lose this hunting advantage when the pond was cluttered with leaves, interfering with the ripples. 

"I wouldn't like being in the same situation," Halfwerk said. "It frightens me a little bit." 

(Reporting by Will Dunham; Editing by Amanda Kwan)