Songbirds—Virtuosos That Defy Understanding
“IN THE early morning hours, I was awakened by sounds strange to my citified ears. Strange but lovely. It was of birds singing. Not just one or two but many. Many birds. Some nearby, others more distant, and all of them singing. As I lay in bed and listened, a growing wonder came over me. I got up and went to the window, opened it, and got down on my knees with my elbows resting on the sill. Much nearer now, I heard the volume swell until it seemed that all outdoors was alive with music. Many songbirds with their many individual songs but all blending in one grand chorus. I ignored the chill in the air. I was enthralled.”
The foregoing was experienced by a man from New York City who was visiting friends in North Yorkshire, England. Their home was surrounded by open fields and woodlands—and birds. When he greeted his host and hostess that morning, he was exuberant. They explained to him that he had just been exposed to the ‘dawn chorus.’ It happens every spring and into midsummer. There is also an ‘evening chorus.’ More subdued, but still impressive. In many parts of the world, these performances are becoming rare; in other areas they have ceased altogether.
There are some 9,000 known species of birds, about 5,000 of which are classed as songbirds, of the suborder Oscines. While some females sing, it is the males that put on these morning and evening musical extravaganzas. We are told that they are singing to hold territory and secure mates, but it’s also just possible that they enjoy making music. Certainly, when the dawn chorus builds to its climax and continues unabated for 30 minutes, the singers do seem to reach festive heights.
Songs of Great Variety
The songs vary from simple to complex to elaborate. The white-crowned sparrow seems content with one simple song, repeated endlessly. The song sparrow has a larger repertoire, wrens have hundreds, and mockingbirds can go on for hours with their melodious outpourings. For sheer number of songs, however, the brown thrasher is credited with over 2,000. Nightingales, thrushes, thrashers, finches, robins, meadowlarks, blackbirds, warblers, cardinals, superb lyrebirds, robin chats, skylarks, and many others from all parts of the earth can claim fame as virtuoso performers.
In addition to the primary songs of the dawn and evening choruses, there are others. Of special interest are the “whisper” songs, subdued renderings of snatches of primary songs, with variations and additions and audible only a few yards away. Often sung while the birds are sitting on the nest incubating eggs or hidden away in the privacy of dense underbrush, these little muted songs sung by both male and female may reflect a quiet contentment.
The mated pairs of many species of birds sing duets. Together, they may sing the same song, or different songs, or sing alternately different parts of the same song. They do it so perfectly timed that it sounds as if just one bird were singing. The interval between when one stops and the other starts is measured in milliseconds. The only way to be sure that two singers, not just one, are involved is to stand between them. In South America outstanding duettists are the musician wrens, considered by many to sing the most beautiful songs heard in the forests there.
Vocal mimicry is a favorite practice of several species. Ornithologists refer to it as a puzzling phenomenon and fail to see that it serves any function, although one researcher suggested that the birds were just playing. In North America the mockingbird excels at it. Its scientific name Mimus polyglottos means “many-tongued mimic.” In just an hour’s singing, one reportedly imitated 55 species of birds.
But the mockingbird holds no monopoly on mimicry. In Australia the superb lyrebird has “one of the most powerful and melodious of all bird songs,” yet “to his own song he adds those of nearly every species living nearby.” Robert Burton, in Bird Behavior, pages 130-1, reports on the mimicry of bowerbirds, marsh warblers, and canaries. The Australian bowerbirds “have been recorded as imitating cats, dogs, axes chopping wood, motorcar horns and fence-wires twanging, as well as many kinds of birds. One bowerbird is said to have mimicked an eagle so well that it caused a hen and her chicks to run for cover.” Certainly, these bowerbirds were not singing to mate with axes chopping wood or to chase twanging fence wires from their territory! Perhaps they were just having fun, as were the people listening to them.
The marsh warbler of Europe pilfers so much from others that “the full range of its plagiarism was only realized through a study made in Belgium. Analysis of sonagrams revealed that probably the entire repertoire was made up of mimicry. Not only were the songs of nearly a hundred European species recognized in the sonagrams but also those of over a hundred African species, which the marsh warbler would hear in its winter quarters.”
Canaries “are undiscriminating and will copy anything, which makes them so popular as cage-birds. There is the famous example, from the early 1900s, of the Eurasian bullfinch which had been taught to whistle ‘God save the King’. A canary in the next room learnt the tune over the course of a year and, when the bullfinch hesitated too long at the end of the third line, the canary would chime in and finish the tune.”
The different species have definite preferences when it comes to platforms from which they will offer their renditions. Some sing from the ground, others from tips of weeds, others from an exposed perch at the top of a tree. Mockingbirds choose such exposed places high up and from time to time launch themselves into the air 10 or 20 feet [3-6 m] and drop down to their perches again, singing all the while. Birds that nest in open fields often sing in flight while soaring over their territories. This is the case with the skylark, as shown by the poet Shelley in his beautiful “Ode to a Skylark,” in which he speaks of this “blithe spirit” soaring high and pouring forth its heart “in profuse strains of unpremeditated art.”
Spring and early summer is the time for the dawn and evening choruses. Even the Bible indicates that this is the special season for the birds to sing. The Song of Solomon speaks of the time when winter is past, the flowers are blooming, fruit is forming on the trees, the migrating birds have returned from their winter quarters, and “the birds will sing, and the turtle-dove’s cooing will be heard in our land.” (Ca 2:11, 12, The New English Bible) Many birds, however, will continue to sing after spring and summer, after mating and nesting activities have ceased.
One writer says that much about birdsong is puzzling, and “the greatest mystery is why these elaborate outpourings should have evolved in the first place,” so “unnecessarily elaborate for any likely function.” Perhaps he should consider that these “elaborate outpourings” did not evolve in the first place but that Jehovah God, who shows concern for sparrows and for mother birds sitting on their nests, gave them these musical gifts when he created them. (Deuteronomy 22:6, 7; Matthew 10:29) Maybe one of the ‘functions’ is to give the birds pleasure. Mockingbirds and some others often sing late into the night. Who is to say that it is not for their own enjoyment—and ours.
How They Do It a Continuing Mystery
The “greatest mystery” may not be why they sing such elaborate songs; it may be how they do it. There have been different theories, and even now after intensive scientific investigation, there is no unanimous agreement. The bird’s voice box is called the syrinx—a bony, boxlike resonating chamber with elastic membranes controlled by special muscles. It varies greatly in different species, its most complex form being found in the songbirds. It is located at the lower end of the trachea, or windpipe, and has two separate sound sources. Each sound source has its own set of nerves, muscles and membranes, which is why songbirds are said to have ‘two voices.’ By alternating muscular tension on the membranes and changing the air pressure, the bird varies volume as well as pitch. Birds with the most syringeal muscles have the greatest potential for producing different complex songs or calls. The most versatile of these feathered vocalists have from seven to nine pairs of these muscles.
Robert Burton in his book Bird Behavior shows why the singing feats of birds are beyond our comprehension: “Sound production reaches its peak in species such as the reed warbler and brown thrasher which sing two tunes at once with different notes coming from each half of the syrinx at exactly the same instant. At one point in its song, the brown thrasher actually utters four different sounds at once, but it is not known how this feat is achieved.”
For the last 20 years, the accepted theory of how birds sing was based on the syrinx alone. Its ‘two voices,’ capable of simultaneously producing two unrelated tones, with each one acting independently of the other, were said to be fully responsible for the quality and variations of birdsongs. After the two sounds leave the syrinx, they must travel up the length of the windpipe before they come out of the mouth. No role in song production, however, was given to the windpipe and its resonances.
In the last few years, a new theory has emerged as a result of intensive scientific investigation. It calls for a “cooperative coupling between the two syringeal sources” and the active participation of the trachea as a resonating, or vocal, tract. The picture emerging is one involving “close coordination between events in the syrinx and configurations of the vocal tract. This coordination is designed to achieve constant readjustment of resonances, with what must often be great speed and precision, to match the changing pattern of syringeal output.” If each “voice” is separately listened to, some of the notes in the finished song are not to be found.
The ability of a songbird to alter its vocal filter is discussed by Stephen Nowicki in an article in Nature: “A bird could adjust its vocal filter in several ways: for example by varying tracheal length, by constriction of the larynx, or by flaring its throat and beak. Such configurational changes could well correspond to the head movements commonly observed in singing birds.” Nowicki concludes: “In contrast to previous theories, birdsong must be viewed as the coordinated output of several motor systems acting in concert.”
Researchers differentiate between bird voices and the clear whistles songbirds use. N. H. Fletcher, writing in the Journal of Theoretical Biology, says that the pure tone whistles in bird song do not seem to come from vibrating membranes in the syrinx but by an entirely different mechanism, possibly “produced by purely aerodynamic means, without the aid of mechanically moving surfaces.” Those lovely liquid notes used by some of the virtuosos still defy understanding.
Jeffrey Cynx of Rockefeller University Field Center offers this tidbit: “Readers may be delighted or humbled to discover that the mastery of absolute pitch can be found in songbirds. . . . My colleagues and I have tested a number of species of songbirds for absolute pitch perception, and found the ability to be rampant.”
Beautiful to Them, Beautiful to Us
“As scientists studying animal behavior,” Stephen Nowicki and Peter Marler wrote in Music Perception, “we are often so engrossed by the functional and evolutionary significance of birdsong as a communication signal that we forget the powerful aesthetic feelings it holds for us as a kind of natural music.” They then recalled that some scientists in the 1920’s and thereafter “suggested that birdsong must be viewed as primitive art, beautiful from the bird’s point of view as well as our own.”
The whisper songs of the mother bird on the nest, the duets of the musician wrens in deep forests, the skylark’s profuse strains of unpremeditated art, the bowerbird when mimicking an eagle so well that a hen and her chicks run for cover, the mockingbird’s outpourings in the wee hours of the morning, and all of this climaxed by the grand dawn chorus that sets all outdoors alive with music! Surely, this should go far beyond statistics and sonagrams. The performances of the birds may defy our understanding of exactly how they do it, but that mystery should only heighten our heartfelt appreciation of those wonderful songbird virtuosos and for the God that made them!
[Pictures on page 16, 17]
Upper right, clockwise: Red-browed finch, satin bowerbird, song sparrow, variegated wren, eastern meadowlark
J. P. Myers/VIREO/H. Armstrong Roberts
T. Ulrich/H. Armstrong Roberts
[Picture Credit Line on page 15]
Paul A. Berquist