Every other Friday, the Outside/In team here at NHPR answers listener questions about the natural world. Today's question comes from Andy, calling from Dover, New Hampshire.
“What is the benefit to a million frogs all loudly croaking in the same tiny pond?”
Producer Marina Henke looked into it.
Transcript
This has been lightly edited for clarity.
Marina Henke: A few years ago I was camping in Maine and couldn’t sleep. That’s because it sounded like this…
(Field tape of many frogs loudly croaking)
Marina Henke: That’s a whole bunch of frogs, calling out around a pond. Why do they do this?
Alejandro Vélez: That is a great question. And, I know it can get loud and sometimes very loud.
Marina Henke: That’s Alejandro Vélez, an assistant professor at the University of Tennessee in Knoxville. He’s an expert when it comes to frog communication. Alejandro told me that what I was hearing that night was something called a “lek” – that’s L-E-K.
Alejandro Vélez: And it's… a lot of males come together and display. Just call, make sounds, try to attract females.
Marina Henke: Simply put, frogs croak around tiny ponds because they want to reproduce. They flock to water since that’s where the females need to ultimately lay their eggs. These leks mostly happen in the spring, and in most species are made up of males. They make for a pretty crowded dating pool… literally. Which means, there needs to be some strategy. Up first, the male frogs start with their advertisement calls.
Alejandro Vélez: That call has two main functions. The same call helps to repel other males and to attract females. One of the species that we work with around here, it's called Cope's Gray tree frog. And their typical mating call, it's a trill. So it's like, “beep, beep.”
(Beeping of Cope’s Gray tree frog’s advertisement call fades in)
Marina Henke: That chorus of beeps might sound like a duet, but it’s really a bunch of solo performers, vying for their chance in the spotlight.
Alejandro Vélez: If another male gets too close and starts calling at the same time or overlapping their calls, they don't like it, and they switch to producing an aggressive call.
Marina Henke: To the trained ear, those aggressive calls can sound really different. Like those Cope’s Gray Tree Frogs in Tennessee.
Alejandro Vélez: Their aggressive call is more like, “Meh! Meh! Meh!”
(Aggressive call of Cope’s Gray Tree frog fades in)
Marina Henke: At first, the dueling frogs might call back and forth to each other, trying to resolve the argument.
Alejandro Vélez: Or they can even go and physically attack each other until one is declared a winner and then the other one leaves.
Marina Henke: It all might sound rather mesmerizing. But for the frogs, it can be an uneasy time.
Alejandro Vélez: So imagine yourself screaming your lungs out every night. It takes a lot of energy. And not only that, but they’re also calling for predators.
Marina Henke: When a frog’s belting it out, he’s also advertising to predators exactly where to hunt. It’s a cost-benefit analysis that takes place every day in the woods. Does the biological imperative to reproduce overpower putting yourself in harm’s way? This is the power of the lek. The more frogs singing in a group, the lower the individual risk that somebody will get snapped up by, say, a hungry heron. And, there’s evidence that the more a bachelor frog puts himself out there, the more likely he is to find a mate.
Alejandro Vélez: What predicts that a male will find a mate or reproduce in one season is typically how many nights they're out there calling. So if they're out there at the bar every night, they will likely find a pair.
Marina Henke: No risk, no reward.
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER.
