Birdsong—Just Another Pretty Tune?
THE distant spotlight begins to cast its light on the members of the chorus as they take their places, dressed neatly for the performance. Trained from infancy in the family tradition, each one sings out with ease. A few among them even appear skilled in the art of improvisation, spontaneously creating new and different tunes.
Where is the performance held? It is not in any world-famous concert hall. Rather, the curtain of the night’s darkness rises to reveal a vast array of little feathered creatures. Songbirds of many kinds, on trees, fences, and telephone wires, blend their voices in one of the most delightful choruses in the world. Their trills, grace notes, whistles, and flutelike tones sound a joyous greeting to a new day.
But these are not just pleasant sounds. There is much more to these birdsongs than meets the ear. Why do birds sing? Do the songs have meaning? How do the birds learn their songs? Do they ever learn new ones?
The Hidden Messages
The liveliest serenading occurs in the mornings and evenings. You will likely hear mostly male voices in the chorus. Their message is twofold. To other males it is a stern warning not to cross territorial bounds. To the females it is an invitation from the eligible bachelors. Songbirds develop their own regional songs, similar to the different accents with which a language may be spoken. The distinctive dialect of the mating song will attract females only from the singer’s particular locale. The most vigorous and complicated singing can be heard during breeding season—a show to impress the ladies.
With his tune, the singer tells his whereabouts to friend and foe alike. Therefore, colorful birds and those preferring open spaces wisely avoid boisterous singing that might attract unwelcome attention. On the other hand, well-camouflaged birds and those dwelling in thickly forested areas can sing loudly, to their hearts’ delight, with little danger of being spotted.
At times what you hear may not be the true song of our winged friends but simply a brief call note that establishes contact between mates or keeps a flock together. It could be an alarm call signaling imminent danger, or it may be a call to arms, to mob a cat or other intruder. With their voices, birds communicate their mood—whether angry, frightened, or agitated—as well as their mating status.
Skillful and Talented Musicians
The vocal abilities of songbirds are truly remarkable. Some can sing three or four notes at once. Others can produce up to 80 notes per second. To the human ear, these sound like one continuous note, but birds can distinguish them because of their keen sense of hearing.
Researchers have wondered whether birds have an ear for music. Can birds tell the difference between an organ piece by Bach and Stravinsky’s “Rite of Spring”? The investigators trained four pigeons to peck one of two disks to identify the correct composer and receive a food reward. Before long the pigeons could hear any segment of the 20-minute piece by Bach and select the proper disk. With minor exceptions, they could make the right choice even with music of similar style by other composers.
Certain tropical birds are able to compose and perform duets. It seems that a mated pair will hold rehearsals, experimenting until they create an original composition consisting of phrases that they sing in an alternating, or call-and-answer, fashion. They sing with such precision that to an untrained ear, it sounds like one continuous song sung by a single bird. Each partner can sing either part or do the whole song solo in the absence of its mate. This unique ability apparently helps birds in dense rain forests to locate and identify their own mates.
Composers and Copycats
Just how birds learn and invent their songs is a subject still under investigation, but one thing is sure: Their learning methods are many and varied. Here is a sampling of the variety found in the bird world.
The male chaffinch has his song at least partially fixed in his brain by the time of birth. Even if raised completely isolated from other birds, his song, though abnormal, will still have the same number of notes and be about the same length as the standard song. To develop the pattern correctly, however, he must hear the song of other male chaffinches before he is old enough to sing, and he must hear it again the next spring. Then, like a human professional singer, this feathered virtuoso must perfect his song with practice, practice, practice—trying again and again to match his youthful voice with the tune he has in his head.
The Oregon junco will make up its own songs if it does not hear the native song. But once it hears the plain and simple junco song, it will stop inventing and will sound just like all the others. On the other hand, the Arizona junco will have its creativity stimulated by hearing an adult junco. It will not copy what it hears but is prompted to invent its own unique song.
The strongest evidence that some songs are genetically fixed is provided by “brood parasites.” For example, the cuckoo lays its eggs in the nests of other types of birds, which act as foster parents. When it hatches, how does the baby cuckoo know that it isn’t the same as its foster father and shouldn’t sing like him? The cuckoo song must be firmly implanted in its brain by the time of birth.
So in many cases, birdsong is evidently a matter of genetics. Even if a bird never learns its own native song, it will not simply copy and adopt the song of another kind. Some researchers suggest that a fuzzy pattern of the native song is present in the brain and the bird can scrutinize what it hears and copy the sound that most closely resembles the pattern.
And what brains they have! Scientist Fernando Nottebohm made the startling discovery that the brains of songbirds are lateralized, that is, they are organized according to left and right sides, each with its own particular functions. He also isolated the song-learning capacity to a special area of the bird’s brain. In the developing male canary, this segment actually grows and shrinks depending upon its need to learn new tunes for the coming mating season. Canaries attempt to sing early in life, but even these masters of song do not achieve professional status till eight or nine months of age.
Other songbirds specialize in creating variations on a theme, borrowing an existing song and elaborating on it or changing the order of its notes or movements. Such mimic birds have long been the objects of our fascination, especially those birds that use their abilities to “talk,” or imitate human voices. The copycat singers of the bird world include the lyrebird of Australia, the marsh warbler and starling of Europe, and the yellow-breasted chat and mockingbird of North America. The latter may have dozens of songs in his repertoire, even including an imitation of a frog or a cricket. It is intriguing, indeed, to listen to the mockingbird’s happy medley of excerpts from well-known classics of birddom.
When these winged creatures sing their pretty tunes, not only can you hear but with appreciation you can also listen. Tomorrow’s performance will begin bright and early. Will you enjoy it?
[Box on page 19]
A Familiar Ring
A scientist in Britain noted a familiar ring to one of the songs of several song thrushes. He recorded the song and analyzed it electronically. To his surprise, it was very similar to the electronic chirp of the trimphone, distributed by Telecom, Britain’s phone company. Apparently, the songbirds heard the tune, picked it up, and added it to their repertoire. The serenading thrushes may well have sent some unsuspecting Britishers dashing to the phone.
[Picture Credit Lines on page 18]
Camerique/H. Armstrong Roberts
T. Ulrich/H. Armstrong Roberts