A Natural History of the Senses (29 page)

Despite all the folk wisdom about how important hearing is (including Epictetus the Stoic’s 2,000 year-old axiom: “God gave man two ears, but only one mouth, that he might hear twice as much as he speaks”), most people, given a choice, would rather lose their hearing than their sight. But people who are both deaf and blind often lament the loss of their hearing more than anything else, perhaps none so persuasively as Helen Keller:

The literature of deafness is extraordinarily rich. Writers and thinkers from Herodotus to Guy de Maupassant have written about their own deafness or the deafness of friends and loved ones with poignancy, eloquence, and charm. The interested reader may turn to Brian Grant’s anthology,
The Quiet Ear
, a fine sampler of writings on deafness that spans the centuries and many different cultures. Mark Medoff has written a powerful play called
Children of a Lesser God
, which was recently made into an equally powerful movie. My two favorite books about deafness are
Deafness: A Personal Account
, an autobiography by the poet David Wright, and
Words for a Deaf Daughter
, a classic memoir by the novelist Paul West. From Wright, we learn that his world, though it has little sound in it, “seldom
appears
silent,” because his brain translates movement into a gratifying sense of sound:

West’s
Words for a Deaf Daughter
frequently appears in college syllabuses, but not, as one might imagine, only in courses for or about
the deaf. Lavishly written, with much wit and phenomenological devotion, it also appeals to students of philosophy and literature as a jubilant hymn to language and life. Told in the second person throughout, it addresses and at times impersonates West’s deaf daughter Mandy. And, unlike many memoirs about handicapped children, it isn’t at all maudlin, but rompy, poetic, and concerned with the struggle we all wage to know ourselves and to make ourselves known. These books allow one to eavesdrop on the inner life of the deaf, a special privilege, since many people assume the deaf, especially if they don’t read or write, think differently, dwelling in a no-man’s-land between concept and word. But, as the literature of the deaf makes clear, ideas and emotions find their way through with surprising ingenuity, whether in English, Ameslan, or some other language, from silence to the inner world where words can be “heard.”

An ancient Chinese proverb says: “A bird does not sing because it has an answer—it sings because it has a song.” Few animal sounds are as beautiful as bird song. Once you’ve heard a whippoorwill throwing the boomerang of its voice across the summer marshes, you listen with a new sense of privilege. Baby birds aren’t born knowing their song; they learn the song of their parents. If you raised some birds away from their parents and whistled a different song—the opening notes of Beethoven’s Ninth, say—then they would learn your song, and neighbors might well call them “the Beethoven birds.” Until they get the knack of making real songs, baby birds often babble and chatter and make a lot of noise that doesn’t seem to mean anything. Like human babies, they are discovering the shock of being able to make sounds at all; eventually they learn to control the sounds, and they practice. A voice is an elaborate instrument, which one can use without knowing much about it. But to make sense with it, you really need to know its limits and capabilities. Hence the babblings. Birds speak dialects, as people do. A New Hampshire crow that hasn’t traveled won’t respond to the call of a
Texas crow, but crows from different regions get to understand each other just as fiddlers from different states do when they meet at a convention in the Ozarks.

Some animals hear in much higher or lower ranges than we do, and with a delicacy and finesse that’s astonishing. A dog can tell the difference between the sound of its master’s footsteps and those of other family members or visitors. My family once had a dog that could tell the sound of my mother’s car engine from any other traffic going by the house. In department stores all across America one can now buy a pair of what look like miniature foghorns, which attach to each side of a car. When the car goes about 35 mph, the wind rushing through the horns makes a high whistle that alerts deer, dogs, or other animals to get out of the way. It’s too high to annoy a human ear, but to a dog napping in the road it is like an air-raid siren. Deer are nearly silent, but they hear well. An experimenter in New Zealand was recently able to cause female red deer to go into heat by playing the sound of a male red deer’s mating roar. Fish don’t have outer ears, but they hear vibrations through the water as we hear sounds traveling through air. Some animals can move their ears like small radar dishes, without moving their heads. I’ve seen deer, cats, and horses run through arpeggios of ear twitching. Thanks to a clever arrangement of their ears—one slightly higher than the other—nocturnal owls can pinpoint a sound to within one degree, and the edges of their feathers are softly fringed to muffle the sound of their approach when they are hunting. It might be more convenient to have just one centrally located ear, but having two makes it easier to locate a sound, just as having two eyes provides depth perception. African elephants have big floppy ears that mainly pick up sounds from below, and they produce a low-frequency infrasound too low for us to hear, with which they communicate.
*
Insects often
have ears on unlikely parts of their bodies, such as on their legs or under their wings.

I once knew an aging cat who, when she went into heat, kept meow-screaming
“Now! Now! Now!”
over and over like a berserk harmonica player as she staggered around the apartment, occasionally stopping to thrust her rump high in that feline invitation to mating known as lordosis. Few sounds are as lovely as those made by the tree frogs in Bermuda, Puerto Rico, and other sunny isles. Often not more than an inch long, such frogs sweetly call through the night like tuneful thumb harps. It’s thought that the coqui frogs of Puerto Rico locate sounds by using their lungs. Sound waves hit the sides of the frog’s body, and travel to the eardrum on a pathway through the lungs. In these days of superspecialization, we assume that the body specializes, too, evolving each part for one purpose. But as it turns out, some parts have various chores. Not only frogs, but some snakes and lizards as well, hear through their lungs; in porpoises and dolphins, sound is believed to travel through an oil-filled lower jaw. Not all animals use sound just for hearing. Sperm whales, bottlenose dolphins, and others may be using sound as a weapon. It is thought that they stun their prey with loud “bangs,” the blasts from which can even cause a small fish like an anchovy to hemorrhage internally.

Tonight the crickets are loud and furious, rubbing their wings into strident song. They seem to be singing in unison, but that’s just an accidental felicity. I’m not hearing them talk to one another at all, since crickets communicate in the ultrasonic range, too high for human ears. What I’m hearing is accidental and to them irrelevant sounds made by their scraping wings. If I were to record the chirps and play them back for the crickets, they wouldn’t answer. Animals seem to have their own lanes of sound, ones in which they communicate and to which their ears are most sensitive. If they didn’t, they’d have to shriek all the time to make themselves heard above the din of other creatures.

There are auditory niches. Nature allows an animal a little decorum
and privacy when it comes to its own species.
*
Otherwise, a warning to its brethren would also signal a predator. Of course, this doesn’t always work as it should. One Central American bat, which has a special taste for the frog
Physalaemus
, stalks its prey by sound. It listens for the male frog’s mating call, knowing that the louder the song is, the plumper and juicier the frog will be. This puts the frog in an appalling predicament. Full of sexual longing in the steamy tropical night, it must sing loudly to attract a mate—but if it does, it may also attract a hungry bat. And yet a poor song attracts neither.

One day in December I went with bat expert Merlin D. Tuttle to Bracken Cave in Texas, a nursery cave where millions of mother and baby bats live. Just before sunset, we sat down in the natural amphitheater of stone outside the cave and waited for the thrilling spectacle we knew was ahead of us. As a ruddy sunset began, a few bats flew out of the cave, circled to gain altitude, and flew off into the night to feed; then a few more came, and dozens after that, and hundreds after that, until suddenly the sky was thick with them. Merlin and I could feel the strong breeze they made as they identified us by echolocation and flew close to our heads without hitting us. Then Merlin swung an arm up fast and grabbed one out of the air, holding it carefully so we could look at its adaptations for echolocation, obvious even in the skin on its face: little folds and flaps that work like radar dishes.

Bats whistle or call to their prey with a steady stream of high-frequency clicks. For most of us, their vocal Braille is too high to hear, since bats click at an average of 50,000 cycles per second. In our youth, we could hear only sounds of up to 20,000. Bats click at intervals of ten or twenty times a second, and the “bat-detector” naturalists use translates the ultrasonic noises into warbles and clicks audible to human ears. Like winged megaphones, bats broadcast their voices, then listen for the sounds to bounce back at them. As they close in on their prey, echoes start coming faster or louder and,
judging the time between the echoes, a bat knows how close its prey is. The solid echoes a bat hears from a brick wall or the ground sound different from the fluid echoes of a flower or leaf. A bat can build a complete echo picture of its world, a canvas on which all the objects and animals reveal themselves in detail, down to their texture, motion, distance, and size. If you stand in a quiet yard filled with bats, the bats will be shouting very loudly; you just won’t hear them. In
The Scale of Nature
, biologist John Tyler Bonner offers this way of putting echolocation into human terms:

Echolocation is just one of many animal sounds beyond our hearing. Praying mantises use ultrasonics; elephants and crocodilians use infrasonics. Few animal displays are as thrilling to watch as the “water dance” of a male alligator. Stretching its enormous head out of the water, it puffs up its throat, tenses hard like a body builder, and then a rolling thunder-buster bellow splits the air, and the water sizzles all around its body, raining upward like frying diamonds. We see the water dance, but other alligators hear its infrasonic signal, made only by the males, perhaps as a courtship display or perhaps also as a full-body raspberry directed at other males. Although female alligators bellow, too, and even slap their heads on the water from time to time, they don’t do a water dance. But they do read its message like seasoned code-breakers. And occasionally a male, hot and bothered and truly inspired, does a cluster of water dances—as many as eight or nine—in a long ballet of dance, song, and yearning.

We also don’t hear most underwater sounds, and that leads us to assume that the vast oceans are silent, which couldn’t be farther
from the truth. Leonardo da Vinci once suggested dipping an oar into the water and listening, with one’s ear against its handle. Fishermen in West Africa and also in the South Seas discovered the same trick. Using the oar as a kind of listening straw, you can hear the sounds of the underwater world. Some fish are a noisy lot. Sea robins, drum-fishes and many others make sounds with their swim bladders; croakers grunt loud enough to keep China Sea fishermen awake at night; Hawaiian triggerfish grind their teeth loudly; the male toadfish growls; bottlenose dolphins click and squeak like badly oiled office chairs; bowhead whales purr and twirp; humpback whales put on a songfest. The ocean looks mute, but is alive with sounds from animals, breaking waves, tidal scouring, ship traffic, and nomadic storms, locked within the atmosphere of water as our sounds are within the atmosphere of air.

How empty the world would be without animal sounds. The blackbirds quibbling like druids. Horses galloping on a soft track. The crows, which sound as if they’re choking in the trees. The burbling chickadees hanging upside down from the branches. The elk’s bugling, like the sound of distant war games. The metallic
ping
of nighthawks. The kindergarten band of crickets (from the Old French
criquet
, “to creak”). The electric whine of hungry female mosquitoes. The Morse code of the red-headed woodpecker.