We all have our favorite singers, but none of them can match the skill of nature's feathered songsters – the birds. As you listen to their spring music, have you ever wondered how birds sing?
The human voice is produced in the larynx (LAR-inks), commonly called the voice box. It is located in the upper part of the trachea (TRAY-key-ah) or windpipe. Bird songs and calls, however, come from deep within the bird. They are produced in a tiny, two-pronged organ called the syrinx (sip-inks) which, as a rule, lies in the chest at the lower end of the trachea and forks into the bronchial (BRON-key-al) tubes that lead to the bird's lungs. Although quite small, the syrinx is very efficient and can produce a song that is variously loud and clear or soft and muffled.
Sound occurs as air from the lungs passes over thin, delicate membranes within the syrinx. This passage of air causes them to vibrate, as our human vocal cords do. Special chest muscles change the tension of the membranes to produce the various sounds. In some bird species each bronchial tube produces its own music and operates individually. When both are used, the songbird actually is singing an internal duet with itself. Structure of the syrinx varies with the species and determines whether the bird's song comes out a whistle, croak, buzz, warble, or combination.
Melodious as bird songs seem to our ears, we can hear only a portion of the complex sounds some birds produce. Their songs may range from less than an octave to almost two full octaves, but the frequency or pitch of the notes many birds sing is too high for us to hear. Since bird notes seldom remain on the same pitch from moment to moment, slurring up, down, and in both directions, our ears often cannot separate even the notes that are in our hearing range. Up and down variations in the wood thrush's song may be as rapid as two hundred per second. With the help of electronic equipment, researchers now are able to record the wavelengths of these high-frequency, high-speed bird sounds and are learning more about them.
The top note a male tenor can attain is in a bird's low range, but a soprano's range of 250 to 900 cycles per second comes close to the 275- to 1,400-cycle range of the jay. A violin goes up to 3,000, and most songbirds can reach the 4,000 cycles of the piano. Wrens, starlings, and song sparrows reach high frequencies of 7,700 to 8,700 cycles per second, and other songsters can go even higher.
Although poets, romantics, and storytellers would have you believe birds sing just to spread joy throughout the land, the complex calls and songs actually are the birds' way of talking. Through the language of song the male bird proclaims the boundaries of his territory and sends out a warning to his rivals. From various points around his territory he announces that this bit of land is taken. If a male establishes his claim in an area where he is challenged by one or more rival males, he must sing more often to maintain ownership of his territory. Intruders usually can be driven away with a song instead of a fight. Bird songs are used to invite the attention of the opposite sex and help maintain the relationship between the female and male throughout courtship and rearing of the young.
Warning calls are used to alert the flock or family group of danger. A crow sentry sounds the alarm to the ground-feeding flock when all is not well, and the female duck quacks a warning for the young to hide when danger is near. Birds living or traveling together also have calls that are used to hold or gather the flock together. For example, when quail are scattered by the hunter or his dog, covey calls bring the group together again.
Most birds have a distinctive family song, consisting of a series of notes with a recognizable pattern and rhythm. The naturalist who learns these family songs can identify the species even when the bird is hidden from view.
Some calls are made by instinct, but research has revealed some interesting things about the adult song. At Cornell University some young bluebirds were raised in isolation so they could not hear the songs of any birds. During the first six months the isolated birds sang only call notes of distress and alarm, which researchers believe are inherited calls. At the end of the six months, recorded songs of the robin, oriole, and thrush were piped in, but the young bluebirds paid little attention to them. However, the reaction was amazing when the adult bluebird's song was played. The young birds cocked their heads, seemed to listen closely, and then attempted to repeat the sounds. Within five minutes all the young were singing recognizable bluebird songs.
A few birds borrow songs from their neighbors. The best of these mimics, the mockingbird, has been known to imitate dozens of other birds. A mockingbird's medley may start with the oriole's song, but before it is through bits and pieces of the songs of the cat-bird, robin, thrush, and others may be tossed in. One report claims a mockingbird imitated fifty-five different birds in one hour of singing, quite an accomplishment.
Birds tend to sing most frequently during the breeding season. The air seems filled with song, especially in the early morning and late afternoon, which are peak singing periods for many species. Whippoorwills and owls prefer the night for their songs. If the day is dark and cloudy, they may start singing earlier in the evening and continue longer into the morning. Bird singing is governed by light rather than time of day. Weather also affects singing. Excessive morning coolness or mid-day heat may reduce singing, but mild temperatures increase the activity. Strong winds and heavy rain also stop or reduce singing, but periods of high humidity before and after a rain may cause birds to sing vigorously.
Next time you hear a bird's song, enjoy its beautiful notes and be thankful we can hear even a portion of its musical language.
1989 – Bird Songs: Introducing Birds to Young Naturalists. The Louise Lindsey Merrick Texas Environment Series, No. 9, pp. 12-14. Texas A&M University Press, College Station.