Here’s a great case of real life turning out to be stranger than fiction. Storybooks often show male frogs croaking by ballooning the bottoms of their mouths out in one fat, round bubble. But only half of frog species croak that way. The rest use a huge range of body parts for their ribbitting.
Some males use a pair of brilliant blue puff-out disks. They look sort of like padded headphones that have slipped down the frog’s neck. Other species have sacs that look like khaki-colored-balloon Mickey Mouse ears. Still others ribbit with a single upright sac. It looks a bit like a fat rhino horn on some inflatable swimming pool toy.
In a new study, two herpetologists looked at 4,358 species of frogs and toads. (Herpetologists are experts on amphibians and reptiles.) All together, the team found frogs and toads had evolved 20 basic forms of vocal sacs. And about one in every six of the species studied had no vocal sacs at all.
Agustín Elías-Costa and Julián Faivovich did the research. Both work at the Bernardino Rivadavia Natural Science Museum. That’s in Buenos Aires, Argentina. The two shared their findings March 7 in the Bulletin of the American Museum of Natural History.
Vocal range
The team studied 777 specimens over 10 years at museums around the world. “Libraries of nature,” Faivovich calls them. Just drawing a picture of something doesn’t confirm its details the way a preserved specimen does.
Their survey showed that vocal sacs disappeared between 146 and 196 times across the frog and toad family tree. That’s “an astounding number considering their biological importance,” Elías-Costa says.
Even animals without sacs still emit sounds. Like human speech, frog and toad ribbits come from the larynx. Vocal sacs make the sound louder. They convey how attractive a male frog is, too. But they can tip off eavesdropping predators.
Female frogs of a few species also vocalize. But mostly it’s a male endeavor.
Frogs and toads search for mates in a wide range of settings. Some meet up at the edges of lakes. Others hook up in cozy tree holes. Some even find each other in tiny pools at the sunken centers of bromeliad leaves. Every locale has different risks and acoustic issues. Frogs must have different types of vocal sacs to succeed in each.