HOW COME? Making sense of calls in the wild

How can bullfrogs and crickets make such loud noises? asks a student.

It's a familiar sound after dark in the country: A vast chorus of crickets, punctuated by the occasional bass-voiced (and amazingly loud) bullfrog. CROAK.

The North American bullfrog is only 4 to 8 inches long, but his guttural voice can carry for up to a mile. Scientists think male bullfrogs call to attract females or to intimidate other males. Just like our own voices, a bullfrog's call starts in his vocal cords, a kind of valve that uses expelled air to produce pulses of sound.

But instead of simply projecting the sound out of his mouth cavity, a bullfrog's croaks take a detour - through his ears. By covering a bullfrog's ears, researchers found that the croak's loudness dropped dramatically.

How does it work? According to Cornell University researcher Alejandro Purgue, sounds travel through a bullfrog's throat and vocal sacs to the frog's eardrums. Like the drumheads on a real set of drums, the bullfrog's eardrums resonate at certain frequencies. For a bullfrog, this means most of the frequencies found in his call. Purgue says that the eardrums radiate an astonishing 98 percent of the energy in the call. And as a bullfrog lets out his croak, he says, you can see the eardrums move.

While a bullfrog's croak stands out from a cricket's chirp, crickets are surprisingly loud themselves. When you hear a field cricket chirping on an August evening, chances are it's a male, since it's male crickets that do the "singing." But contrary to a popular myth, it's not a cricket's legs that make the night music. Instead, crickets use two of their four wings to orchestrate their chorus of chirps.

How? First, a cricket raises his front wings about 45 degrees. Then he draws a thick, ribbed vein on one wing over a ridge of wrinkles on the other. Like drawing a bow across the string of a violin, the result is a kind of music. The volume is turned up courtesy of a cricket's raised wings. The wings act like the sound board on a violin or guitar, amplifying the notes produced by the rubbing ridges.

Scientists think a male cricket sings mainly to attract the attention of a female, like a guitar-strumming Romeo serenading his Juliet under a window. But crickets also have threat songs, warning off other males. And they may chirp an alarm when a predator (such as, you guessed it, a bullfrog) is in the vicinity. The result? Nearby crickets observe a moment of shielding silence.

Scientists have discovered that a cricket's brain can temporarily turn down his hearing, muffling the sound of his own deafening singing. While crickets don't have ears like ours, they do have eardrums . . . on their front legs. Like multitasking bullfrogs with their amplifying ears, cricket legs do double duty. They may not sing with their legs, but crickets do hear with them.