CHAPTER 6
Singin’ in the Rain: Bird Vocalizations
On a frigid winter morning as I walk through the woods, when even the wind is silent, the sound that penetrates my warmest fur-lined hat is the rich song of a cardinal, or another song lovely in its simplicity — the Hey, sweetie! of a chickadee. By spring, birdsong erupts well before dawn, and the morning chorus has so many voices that it may be hard to pick out that same cardinal and chickadee, but they’re in there. The beautiful voices that fill the spring air make the whole world seem alive and happy.
How do birds produce such complex sounds? Why do they sing? And how do we learn to identify their voices? Those are the questions people send me.
Making Beautiful Music
Q I went on a bird walk and my leader pointed out a Wood Thrush song. It was cosmically beautiful! How can a single bird produce such an amazing sound?
A Because birds produce their sounds with their syrinx, or song box, which has two branches and two sets of muscles, they can produce harmony with their own voice. Birds in the thrush family have very complex muscles in their syrinx, allowing them to produce breathtakingly complex tones independently in each branch.
That morphological description may begin to explain how the individual tones are produced, but what can explain the sheer beauty of these sounds? Do male Wood Thrushes take as much pleasure in singing as we do in listening to them? Do female Wood Thrushes select mates for a dry, analytical reason such as how many different tones in what arrangement each male sings, or because the beauty of a song takes her breath away? Science gives us a lot of answers, but it might take the Vulcan Mind Meld to resolve that one.
Q I live in the woods in northern Minnesota, and in May and June I usually wake up to a Winter Wren singing near my cabin. How does such a tiny bird produce so many sounds so quickly?
A As with other splendid bird songs, our experience of Winter Wrens transcends a mechanical understanding of sound production. In 1884, the Reverend J. H. Langille described his experience listening to the Winter Wren, “I stand entranced and amazed, my very soul vibrating to this gushing melody, which seems at once expressive of the wildest joy and the tenderest sadness.”
Per unit weight, Winter Wrens have ten times the sound power of a crowing rooster, and birds in the Eastern population sing a good 16 notes per second — an impressive output that is not only exceeded but more than doubled by Western birds, which sing 36 notes per second! Their rapid heartbeat, respiratory rate, and metabolic rate don’t explain the output, since larger and smaller birds don’t match this! But what is even more amazing is that these birds not only produce the sounds but react to tiny parts of the songs, so their ears and brain can resolve in real time individual notes that we cannot without replaying the songs at slow speed.
Q Why are bird calls so varied? Cardinal and Mourning Dove calls are so different from each other, for example. Is there something in their physical makeup that makes the sounds distinct?
A Yes. The size of the bird and length of the trachea and bronchial tubes impact the sound quality and frequency, and produce sounds in their syrinx, which is far more complex than our human larynx. Although our larynx is a simple instrument, made of a muscle that spans the trachea and can be controlled to make varying sounds, human voices are still so variable that most of us can recognize dozens, and sometimes hundreds, of individual people by their voice.
The syrinx is located where the trachea branches into the bronchial tubes and, depending on the species, may have a variety of muscles arranged within this more complicated framework. When a group of people sing together, we make up a chorus. When birds do, it’s more like a whole symphony orchestra.
NAME THAT TUNE
Describing bird sounds can be tricky. For example, I once received this question: “Could you tell me what bird is most often the first to sing in the morning, and sings all day. I hear it most of the year except in winter.”
Robins are usually among the very first birds to pipe in with the dawn chorus, so I sent him to a Web page with the robin song and told him that if this wasn’t it, to please try to describe how the sound of his bird was different. He wrote back, “This bird has a two-sound cadence — a short sound and a very long ending that runs for maybe two seconds. I normally hear this bird near water or marshes.” I still didn’t have a sense of its tonal quality, so I asked if it sounded buzzy like a Savannah Sparrow, with another link. He responded, “No, it’s more melodic — a long pitch sound like the bird is saying hel-lowwwwwwwwwwwwwwww.”
Then it hit me. He was describing a White-throated Sparrow. When I sent him a link to that sound, he was ecstatic. Detective work can be ever so rewarding.
Scientists describe bird songs using sound spectrogram, or a sonogram — a graph showing each tone’s frequency and duration. Some practice or training are necessary to interpret them.
Rather than describe a song at all, people now often email me recordings. They don’t need a fancy microphone — many just point a digital camera toward a singing bird and use the video function. Whether or not we can see the bird, this lets us hear it!
Q My wife and I moved to Dallas in January. As the weather has warmed, we’ve come to expect a high-pitched twirp in the twilight at dusk and dawn. It sounds like some swallow, and I assume that it’s feeding on insects, though I don’t know how it sees them in the darkness. I don’t think this is bats — there are too many. How can I figure out what bird this is?
A It’s very tricky to describe sounds in a way that someone else can “hear.” But I would bet your birds are either Common Nighthawks or Chimney Swifts. Nighthawks make a funny beep! or peent! in the twilight sky as they catch insects. Chimney Swifts also feed in low light, and you’re apt to hear them because they gather in large congregations to roost. How can you tell which one this is unless you get a good look? Go to www.allaboutbirds.org and type in just about any North American species name and you can listen to its sounds.
The number of different songs that a bird sings varies depending on the species and the individual bird. Chipping Sparrows repeat the same single song over and over. Northern Cardinals sing 8 to 10 songs, American Robins 70, and Northern Mockingbirds 200. Brown Thrashers are the record-breakers, however; they are mentioned in Ripley’s Believe It or Not! for their amazingly huge repertoire of 2,000 songs.
FEMALES WHO SING
When I took an ornithology class back in the 1970s, we learned that male birds do the singing and females do the listening. This seems obvious intuitively: males are the ones with conspicuous plumage and the job of defending the territory while females incubate eggs, usually trying to be as inconspicuous as possible. And it’s true that many or even most songs we hear from familiar backyard birds, from mockingbirds to Chipping Sparrows, are sung by males.
But females of many tropical species sing, and also females of several northern species, including Northern Cardinals, Black-headed Grosbeaks, Rose-breasted Grosbeaks, and White-throated Sparrows. Scientists are still teasing out the reasons why some females sing while others don’t — this is yet another area where the more we learn, the more questions we come up with.
Female White-throated Sparrows have a very interesting and unusual singing pattern. The species has two color forms — one has white stripes on the head and the other has tan stripes. This is a genetic difference like that underlying human eye color. Birds of either sex can have head stripes of either color.
Both male and female sparrows with white head stripes are more aggressive than tan-striped birds. Female white-striped birds sing, but tan-striped females do not. In laboratory tests where birds were separated by a glass partition but could see those of the opposite sex through the glass, females of both color forms preferred tan-striped males, but the more aggressive white-striped females outcompete the tan-striped females for tan-striped mates. Those same laboratory tests indicate that males prefer the appearance of white-striped females, but that when white-striped females start to sing, the aggressive white-striped males attack them. So virtually all pairs of White-throated Sparrows have a male and female of opposite color forms.
What Do Birds Sing About, Anyway?
Q The cardinal outside my window has been singing all morning. Why does he spend so much time singing?
A He sings to attract a mate and to announce his presence to other males so they will stay off his territory. Some birds sing tens of thousands of songs each day. Defending a territory requires constant vigilance!
If you listen carefully, you may hear countersinging, when neighboring birds sing in response to each other. When Marsh Wrens countersing, they may match each other by singing the same song type as a neighbor. Or they may sing an entirely different song type, or anticipate the song the other will sing next and sing it first. All these choices allow males to communicate their intentions before deciding whether to fight. Depending on how they sing, they can direct threats to specific neighbors or back down from a challenge.
In addition to vocal sparring, birds may use their repertoires to impress potential mates. Male Song Sparrows with larger repertoires have a longer lifespan than do males with fewer songs. This is probably because males that are better nourished and defend better territories are able to learn more songs.
Young male Bewick’s Wrens that hatch early in a season have more time to learn songs before winter than later-hatching males do; those with more songs in their repertoire can successfully defend the best territories. In these species, females prefer to mate with the males with the most song types, an easy way of discerning which males are robust and experienced, and thus, most likely to help her successfully raise healthy young.
Q My son says he’s been tired lately because the birds wake him up at dawn. Is it my imagination, or do the birds sing especially loudly at first light?
A It’s true: more birds sing at dawn than later in the day, and they sing with more energy and variety. This “dawn chorus” actually starts an hour or so before dawn in spring and early summer. The chorus often begins with American Robins singing a much more rapid, excited version of their daytime song. Chipping Sparrows sing their songs at a frenetic pace, and many other birds sing with exceptional energy as well. As more birds join in, the chorus crescendos. At its peak, the dawn chorus can be so richly complex that it can be tricky for human ears to pick out many of the individual voices.
Ornithologists are still debating why birds sing so vigorously during the dawn chorus. Do birds simply have a lot of pent-up energy after a good night’s sleep? Is dawn the best time to sing because in the dim light, territorial competitors and prospective mates don’t have much else to do other than listen? Is morning the best time to make a statement to competitors and potential mates that may have landed in the morning after a night of migration? These exceptional dawn choruses are also most common in the temperate zone, where birds have a compressed breeding season lasting only a few short weeks.
Whatever the reasons for it, the dawn chorus is one of the truly spectacular yet everyday occurrences that most of us take for granted. If the birds wake you up in the morning, consider stepping outside to listen, or even getting up before dawn and going to a natural area near you, where you’ll experience an even more unforgettable show.
More than Just Melody
Q I’ve heard mockingbirds singing songs that I know belong to other birds — what’s going on? Why do they imitate so many other sounds?
A Although some birds learn their species’ song during their first year of life, others, including mockingbirds, continue adding to their repertoire as they grow older. Northern Mockingbirds can learn as many as 200 songs and often mimic sounds in their environment including other birds, car alarms, and creaky gates. One theory is that if a female prefers males who sing more songs, a male can top his rivals by quickly adding to his collection some of the sounds around him. Possessing a diverse assortment of songs may indicate he is an older male with proven longevity and survival skills — good traits to pass on to offspring. An older male may also be more experienced in raising young or may have access to better resources.
According to one study on the Edwards Plateau in Texas, mockingbirds with the largest selection of songs have the best territories, laden with foods such as insects, wild grapes, and persimmons. One 2009 study found that mockingbird species in areas with unpredictable or harsh climates include more imitations in their songs than those in milder climates. In harsher areas, it may be more critical for females to be extremely choosy about which mates they accept.
Some researchers have suggested that mockingbirds may use other species’ songs to warn those species to keep away from their territories, but this possibility has never been thoroughly investigated. There is no evidence that a mockingbird song has ever caused a cell phone to head to another territory, even though they imitate those!
At least four American Presidents had mockingbirds as pets in the White House: Thomas Jefferson, Rutherford B. Hayes, Grover Cleveland, and Calvin Coolidge.
MORE MIMICS
The Northern Mockingbird is the best-known mimic in North America, but starlings, in the same family as the mynah, are also famous for their mimicry. Wolfgang Amadeus Mozart had a pet starling that could mimic tunes and make variations of them. Renowned mimics, such as the lyrebirds of Australia and the Lawrence’s Thrush of South America, occur on other continents, too.
Male Marsh Warblers learn the sounds of other species on their wintering grounds in Africa. Perhaps these varied sounds impress potential mates when they return to breed in Europe. Indigobirds in Africa are also mimics, but for an entirely different reason. Indigobirds are brood parasites that lay their eggs in the nests of other species. For example, the Village Indigobird lays its eggs in the nest of the Red-billed Firefinch. Young indigobirds learn the begging calls of the firefinches that raise them so they will not be recognized as an intruder. Young male indigobirds also mimic their hosts.
The female Thick-billed Euphonia is a Neotropical bird that imitates the alarm calls of other species when her nest is threatened. These sounds may get the attention of other species to help in the attack of a predator or other perceived threat.
Some species not typically thought of as mimics sometimes imitate the vocalizations of other species. Blue Jays imitate the calls of Red-tailed, Red-shouldered, and Broad-winged Hawks, for example. The function of these imitations is unknown, but sometimes jays call out a raptor imitation just before flying into a feeder, and when they do this, the birds at the feeder often scatter.
Some observers have noticed that when jays imitate hawks, incubating birds sometimes fly up from their nests, so this mimicry may help jays to discover where nests are. Jays raid nests for eggs and nestlings during their own breeding season, when protein is critical for their own young.
In some cases, mimicry may result from the song-learning process gone awry, such as reports of a Vesper Sparrow and House Wrens singing songs of the Bewick’s Wren, and an Indigo Bunting and a Common Yellowthroat singing a Chestnut-sided Warbler song. It seems that a fairly large number of these occasional mimics are unpaired, suggesting that males who learn the wrong songs often fail to pass their genes to the next generation. Selection against birds who learn the wrong songs may thus be very strong, so “mistakes” are not perpetuated.
Q When I went on a birding trip to the tropics, our guide told us to listen to the sounds of birds that he said were a male and a female wren duetting. Do our backyard birds duet too?
A Interestingly, duets are far more common, complex, and coordinated among tropical birds than they are among species that breed in the temperate zone. For example, a female Red-winged Blackbird may join in a duet by uttering a loud series of notes during the last half of her mate’s oakalee song. In contrast, some tropical wrens sing such highly coordinated duets that unless the birds are far apart, it’s hard for a listener to even realize that more than one bird is singing. Other tropical duetting species include some parrots, woodpeckers, antbirds, flycatchers, shrikes, and wrens.
Birds that are resident in the tropics are much more likely to maintain long, monogamous bonds and to live year-round on their territory. This may provide more opportunity for them to develop complex duetting, which may further strengthen their bond or aid in joint defense of the territory.
Q I’ve often heard the Song Sparrows behind my house singing a beautiful melody, but I was surprised when I heard one make a short little chirp that sounded nothing like the songs. Was it a young bird that didn’t know how to sing?
A Not necessarily. You heard a contact call, a sound that the birds use to tell one another, “Hey, I’m here.” Males, females, adults, and juvenile birds may all use this call year-round. In contrast, it’s typically only male Song Sparrows who sing the more complex melodies. They only sing during the breeding season, to advertise their presence to females and to warn males to stay off their territory. (In rare cases, female Song Sparrows sing, but their song is usually simpler than that of the males.)
Sparrows may also use a variety of other vocalizations to communicate with one another. For example, Song Sparrows utter a high-pitched alarm note that ornithologists describe as a tik when a hawk flies overhead. They use a lower-pitched call described as tchunk when humans approach a nest or fledglings. Females make a harsh chattering sound to their mates during nest building, and they utter a nasal trill after mating. Both males and females “growl” as a threat. When migrating at night, Song Sparrows also make high-pitched tseep calls, perhaps to alert nearby birds to their presence in the dark skies.
Paired-up goldfinches make virtually identical flight calls; goldfinches may be able to distinguish members of various pairs by these calls.
SINGING ON THE WING
Some birds, especially those that live in expansive grasslands or tundra with few conspicuous perches, sing in flight. This allows their voice to carry farther and provides them with a visual as well as auditory display.
At least one forest bird, the Ovenbird, a warbler living in forests in eastern North America, also has a flight song, usually given at dawn, dusk, or nighttime. The bird starts out singing anywhere from ground to mid- or even upper-canopy and suddenly takes off in labored flight, wings and tail outspread as he circles and continues to sing. This display has been nicknamed the Ovenbird’s “ecstasy flight.” The flight song is quite a bit different from the normal teaCHER, tea-CHER, tea-CHER song produced most of the day. The function of this song isn’t understood yet.
Many male hummingbirds have aerial displays, combining a specific flight pattern, often a deep U, with a wing buzz. Male Common Nighthawks display by flying toward the ground and suddenly making a loud boom, produced by air rushing through the primary flight feathers after suddenly flexing the wings downward during the dive.
Male American Woodcocks may engage in evening “skydances” during the spring. Several males gather in an open area near the woods where they spent the day. When the light grows very low, they start producing a buzzy peent vocalization from the ground. Then, one bird will take off, his wings making a lovely chittering sound as he spirals toward the sky. Suddenly he breaks into a chirpy vocalization and drops to the ground to begin anew. Female woodcocks are drawn in by this display.
Q I heard a tremendous racket from birds up in a tree last spring. When I got up close, I could see that they were fluttering around an owl. Why do they make so much noise? Shouldn’t they try to keep quiet and stay away from the owl?
A The birds you heard were uttering alarm calls after they noticed the owl. Many songbirds recognize alarm calls not just of their own species, but of many other birds. They may join a mob of birds making harsh scolding sounds while dive-bombing an owl, snake, cat, or other predator. Together, they may drive the predator away, or at least distract or harass it so that it won’t discover their nests or young nearby, or where they themselves go to roost at night.
Q Once I was walking in the woods and heard a soft, low thumping sound that got faster as I listened. I couldn’t see what was making the sound, but a friend told me it was a Ruffed Grouse. Is that true?
A Yes, male Ruffed Grouse produce a distinctive drumming sound, beginning slowly at first but speeding up into a whir. Because grouse often stand on a log while doing this, people once believed this sound was produced by the grouse’s wingtips beating the log — or that the bird thumped its wings against its breast, Tarzan-like.
But in 1932, Arthur A. Allen hid out near a grouse’s drumming log and caught a grouse on film with his slow-motion movie camera. The stopped frames of the film showed that the grouse stood crosswise on the log, braced on his tail, and cupped his wings, bringing them forward and upward with such force that he compressed a parcel of air between his chest and wings, creating the sound wave without touching his wings to his chest or to the log. The sound is deep, about 40 hertz, which is at the low range of human hearing, explaining why some people say they almost “feel” the sound as much as hear it.
In spring, Ruffed Grouse males declare their territories and announce their presence to females by drumming. Although drumming peaks in April or May, they may drum at any time of year. In fall, you can often recognize a young grouse by his pitiful attempts at drumming. Until a bird masters the trick of cupping the air properly, he may simply produce a dull flapping sound, but as with many skills, practice makes perfect.
If the idea of producing such a sound simply by compressing air in the “wingpits” seems hard to imagine, remember that humans can also produce a sound in our armpits by compressing air. There’s one notable difference between Ruffed Grouse and humans, though — female grouse find their partners’ “pit” sounds attractive.
Q I saw the most bizarre thing on my way to work. A woodpecker flew to a stop sign and pounded on it with its bill. Why was it doing that?
A Woodpeckers usually drum on trees to announce their territories or to attract mates, but the woodpecker you saw took advantage of the metal sign to help broadcast his message more loudly. The farther a woodpecker’s drumming sound carries, the larger the territory he can defend. Different woodpecker species drum with distinctive rhythms. For example, Yellow-bellied Sapsuckers begin with a drum roll, pause, then add some slower strikes. After a sapsucker drums, another sap-sucker may drum back in reply.
Pileated Woodpeckers drum rapidly, about 15 beats per second, speeding up near the end of the burst. They also communicate using other rhythms, such as with a double tap near a promising nest site, or a series of taps from within their nest cavity as a mate approaches to take a turn at the nest.
Q What’s the best way to learn how to recognize different birds’ songs?
A The best way is to track down every natural sound you hear and look for the animal that’s making it. When I was a beginner, I spent three evenings trying to track down a beautiful whistle that I knew had to come from a bird, only to finally find a one-inch tree frog called a spring peeper!
When you search high and low for ten minutes to find one particular singer, you can’t help but remember that sound, bird or not. By tracking down each singer, little by little you’ll also absorb clues about the sound, habitat, time of day, time of year, and other factors experts use to identify birds by ear.
You can listen to audio guides or birdsong recordings on the Internet to help you identify the songs of birds in your area or at another birding destination. It’s often most effective to listen to a few songs at a time and become familiar with them before moving on to the next few. You can also watch a DVD or CD-ROM with video footage of birds singing to help you associate the bird with its song.
Whether listening to recordings or to birds in their natural settings, you can use mnemonics to help you remember the sound. A few examples include the notes of a Black-capped Chickadee (chickadee-dee-dee), the song of a Carolina Wren (teakettle, teakettle, teakettle), and the hoot of a Barred Owl (Who cooks for you? Who cooks for you-all?).
Many songs don’t have a consistent rhythm pattern but are easily recognized by the tonal quality. Crows caw while ravens croak. Rose-breasted and Black-headed Grosbeaks have a song somewhat similar to an American Robin’s, but the grosbeaks have a richer tonal quality than the robin. I describe the difference as that between an opera singer such as Beverly Sills and a movie singer such as Julie Andrews.
Many birds sing a simple staccato trill. When you master the Chipping Sparrow’s song, you can compare similar trills as being shorter (Dark-eyed Junco), slower (Swamp Sparrow), more musical (Pine Warbler), more mechanical (Worm-eating Warbler), and so on. Listening to sound recordings of wild birds will help you recognize those kinds of differences.
Q How do birds learn their songs?
A There are almost as many answers to this as there are species of birds! Some scientists have devoted their careers to figuring this out, species by species.
Some bird songs are hardwired into a bird’s brain. Virtually all flycatchers, including kingbirds and phoebes, fall into this category. If Eastern Phoebes are raised in captivity and never exposed to their species’ songs, they still develop normal phoebe songs.
Marsh Wrens imitate elements of songs they hear. When a Marsh Wren egg was hatched and reared by House Wrens, it produced unrecognizable songs. When exposed to a training tape, captive Marsh Wrens imitate song elements of a few other species. Wild males engage in “matched countersinging” with neighbors, so they continue to learn song elements as adults.
Sedge Wrens seem to improvise their own unique song repertoires. American Robins share some whistles with neighbors, so they apparently learn song elements from one another. Baltimore Orioles may learn their songs from their fathers and neighboring orioles during their first summer. It’s possible to detect differences between songs of yearlings and older males, so orioles adjust their songs at least until they’re two years old.
As beautiful as Hermit Thrush songs are, there has been little study about how they are learned. Wood Thrush songs have three parts. The middle part is apparently learned by listening to other Wood Thrushes. The first and last parts are either innate or invented by the birds. When Wood Thrushes are hand-reared and never hear their song, the middle part is slurred. If they’re exposed to wild “tutors” after they’re a year old, they don’t improve this middle part, so there must be a critical time for learning it during their first year. If hand-reared Wood Thrushes are exposed to tapes with only the middle part of the song, they end up singing a normal song, with the middle part matching the taped version.
Bird songs can carry us away with their beauty. But the more we learn about them, the more thrilling those songs become.
Male mockingbirds may have two distinct repertoires of songs: one used in spring and another used in fall.
BIRDS THAT MAKE SOUNDS WITH FEATHERS
As a Mourning Dove flies past, you may hear a whistle — a sound produced by its feathers. The function is unknown, but some scientists speculate that sound may signal alarm when the birds take off. Male Mourning Doves also use their wings to produce noise when attracting the attention of females. They launch from a perch high into the air, flapping their wings loudly, then glide down as part of a courtship display.
Many other birds also produce sounds with their feathers. Ruffed Grouse make an explosive thunder as they burst into flight. Common Goldeneye wings make a whistling sound in flight that can carry more than a mile. American Woodcock wing feathers make a distinctive twittering sound as the birds fly.
In a territorial display, male Anna’s Hummingbirds plummet through the air nearly vertically from heights of 66 to 131 feet (20–40 m). At the bottom of their dive, they make a loud squeaking noise, similar to a sound they make while singing from a perch. Using ultra high-speed cameras, researchers found that the birds actually produce the dive squeak when they spread their tail at the end of their fall, causing air to vibrate the feathers rapidly. The scientists were able to produce the same sound by blowing a stream of air over a hummer’s outer tail feather.
Similarly, Wilson’s Snipes use their stiff outer tail feathers to produce sounds when they display in spring. The snipe circles high overhead and then drops, speeding up to as much as 52 miles per hour in the dive, while spreading its tail. The vibrations of the two stiff tail feathers produce a peculiar hum as the wing beats send the air over the tail in pulses. The distinctive sound, woo-woo-woo-woo-woo, called winnowing, is audible from up to half a mile away.
Tropical manakins make an array of bizarrely wonderful sounds with their wings, from rapid firecracker-like snaps to tonal hums with their feathers. High-speed video shows that when a Club-winged Manakin flips its wings over its back, it knocks two specialized wing feathers together, creating a high-pitched tone as one feather slides against the other, like a bow on the string of a violin.
