Under the Microscope: Bird song is one of the delights of nature. When I was young my uncle kept a canary in a cage in his pub and he would silence customers when the bird sang in order to enjoy the performance, writes Prof William Reville.
I don't know if people keep songbirds in cages any more. I know it wasn't much fun for the birds but the practice did illustrate the simple pleasure the average person derives from listening to birds singing.
Birds sing in order to communicate with other birds. They have two basic messages: "go away" or "come over here my darling". Birds can probably communicate better to each other through song than the individuals of any other family of creatures can using other means. Song carries a long way and is effective under difficult communication circumstances such as darkness or dense vegetation. Bird song can be very complex. Analysis has shown parallels between Beethoven's Fifth Symphony and the skylark's forest of notes, and between the woodlark's complex song and the 48 preludes and fugues of JS Bach. Other statistics are also impressive. For example, the nightingale knows up to 300 different love songs and the chaffinch sings his song up to a half a million times in a season.
The complex variety of notes in bird song is made possible by the structure of the bird's vocal organisation. The sound-producing organ in birds is called the syrinx. The bird passes air from its lungs over membranes in the syrinx, which vibrate, generating sound waves. The muscles of the syrinx control song details and the more intricate the vocal muscles the more complex the songs. The human sound box is located at the top of the trachea unlike the bird's syrinx which is located lower down where the trachea divides into two tubes. The syrinx has a separate sound source in each tube. These separate sounds can be mixed to produce much more complex and elaborate sound designs than humans can produce.
One gets the impression that birds sing in bursts that last for minutes without catching their breaths, but they actually take many shallow mini-breaths synchronised with the note patterns of the songs. For example, a canary may take 30 mini-breaths a second.
Birds the world over sing most at dawn, and the dawn chorus is one of the best-loved features of nature. Why birds sing most at dawn is not fully understood. One reason may be that sound travels best at dawn when other noise levels are low. Also, birds have time on their hands at dawn. Light levels are poor making hunting and foraging difficult and low temperatures keep insect prey on the ground.
Birds invest much time and energy singing, so there must be a good reason for bird song. The two main functions of bird song are to defend territory and to attract a mate. It is usually the male birds who sing. In most bird species a male bird owns a territory, attracts a female bird to join him there and breeds with her. Males claim their territory by singing short simple songs that carry over long distances detailing the location and identity of the singer. These songs contain gaps allowing the singer to listen for replies.
When wooing females, males sing longer and more involved songs. The females hear the songs but generally do not reply. The male with the most complex and largest repertoire is usually the most attractive to the female. A female will find a male with a large repertoire of complex songs more attractive because, in effect, the male is saying "I would make a good catch because I am such a good food-finder that I have spare time to compose these long complex songs."
Some birds expand their repertoire of songs by mimicking songs of other species. The best bird mimic in the world is the lyre bird found in Australia. This bird can imitate 12 other birds, the whirring of the motor in an automatic camera, the engine of a car, and the sound of a logger's chainsaw.
Although it is usually the male bird that sings, sometimes the female also sings. For example, the male European robin sings all year round but, in winter, the female also sings because the male and the female defend separate territories. They need separate territories in order to gather enough food to get through the winter.
A bird's song proclaims its species identity, breeding status, health and individuality. Zoologists are very interested in bird song because it is so critically important to the reproductive biology of birds. Researchers have studied canary song very carefully and know the rules governing exactly how these songs are structured.
In recent research young male canaries were raised in isolation and exposed only to synthetic songs composed according to rules that differ radically from the rules governing normal canary song. The young male canaries accurately memorised and imitated the rule-breaking songs. However, as the days grew longer and the canaries approached sexual maturity and the breeding season, they began to edit their songs so that they fitted the rules of normal adult canary songs and the expectations of potential mates. The vocal flexibility shown by the very young birds changes into a rule-driven adulthood. Accurately signalling your identity is a serious business for a species. Get it wrong and you don't get a mate.
Further details at www.pbs.org/lifeofbirds/songs.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC