Not all birds sing. In fact less than half the birds on the planet are genuine songsters. The most celebrated songbird is, of course, the Nightingale
Complex and clear tones, songs are like a string of phrases made of sequences of notes, punctuated with the equivalent of commas. Learning and singing songs is actually not easy for birds. The feats they produce for their small size are quite incredible. The European Wren sings a song that contains 740 different notes per minute and which can be heard more than 500 metres away. Considering the comparative sizes of you, me and a wren, this is the equivalent of us singing a song that can be heard 4 or 5 miles away. The Kakapo who has one of the most far-carrying songs of any bird, actually achieves even this 4 mile transmission. Birds don't have vocal chords. They sing by expelling air from their lungs through a syrinx, a kind of voicebox at the bottom of the windpipe whose two sets of membranes and muscles vibrate at high frequencies as air is exhaled. This complex design means birds can produce a far greater variety of sounds than humans emitted at far greater speed.
Birds put an enormous amount of effort into their singing, for some it is as energy intensive as flying. For example a canary needs 30 mini-breaths a second to replenish its air supply. Yet some birds sing practically non-stop through the breeding season
So why do birds sing?
Romantic notions ascribe birdsong to expressions of their love or joy. Although it may be true that sometimes birds may sing for the pure pleasure of it, for the most part, the tweeting of a songbird is serious business.
Birdsong has two main functions: to defend a territory and to attract a mate, and since even in the avian kingdom, this is a man’s job, it is primarily the males that sing. Birdsong is also an accurate measure of a bird’s fitness. Strong birds, who can invest the energy needed for loud, continuous singing, can better find food, evade predators and fight off rivals. So essentially our master musicians are signaling to potential mates, rivals and predators to either "Clear off!" or "Come on!”
Male birds put a lot of effort into learning, perfecting and singing their song. While some species like pigeons don’t have a lot to offer besides cooing, others have more complicated ones involving many different phrases. For example, the cowbird uses 40 different notes, some so high we can't even hear them. British musician David Hindley slowed birdsong down and discovered parallels between the skylark's notes and Beethoven's Fifth Symphony! Nightingales have upto 300 different love songs in their repertoire while the Brown Thrasher has over 2000.
Females spend several days listening to a selection of singing males before making their choice. They prefer males with the largest repertoire and the most complex songs. Males with more and better songs therefore find mates earlier in the season. Getting paired early in the season is important because the sooner a pair can start raising a brood, the higher their chances of successfully rearing a second one. After attracting a mate, the male sings to stimulate her sexually, to make her produce hormones and help her ovaries grow. In some species, the female bird sings in response to the male's song, and her own singing stimulates her reproductive system.
Where and when you sing depends on to whom you are singing and where you live. Male birds that are trying to attract a mate must first ensure they are heard so they will choose the highest or most conspicuous spots available. Every bird tailors its song to its habitat. Birds of the forest floor, such as ant birds and curassows, use low-pitched calls that will not be bounced off and distorted by the ground. Out in the plains, species like the Savannah Sparrow favour the buzz, a compressed message which carries over great distances in open areas and grassland. The high frequency calls of New Zealand blue ducks cut through the babbling, rushing sound of water. Sound travels best a metre or so above vegetation so many small birds sing on elevated perches to minimize interference from the ground and foliage. The nightingale sings its melody from a tree branch from where the song carries a long way. Grassland birds like Skylarks and Pipits sing on the wing, often making 'song flights' to heights around 3-6 metres above ground level. One of the most amazing discoveries is that some birds like the Carolina Wren can judge how far away another male bird is singing not by the volume of the song but by how much it has depleted between its source and reception.
The presence of a singing male is enough to maintain a territory. It proclaims that this territory is occupied and the owner is home. Other male birds respect this. In bird land, possession is at least 9 tenths of the law and the resident bird usually wins any confrontation. So once a mate is found, the male usually switches to a short simple and economical song to keep his territory. Once paired, birds like Reed and Marsh Warblers sing less often and less complicated songs while Sedge Warblers stop singing altogether. The European Robin, on the other hand, sings all year round. Territory maintenance is clearly a higher priority for the non-migratory robin than for the migratory warblers.
Singing to attract mates and defend nesting territories occurs mostly in spring. Birds you hear singing later in the summer may be starting a second brood with a brief courtship, or they may have lost a mate and are trying to attract a new one. There is one bird sound that you will hear only from mid to late summer, the repeated call of fledglings. When a bird first leaves the nest, it flies a short distance to some protected spot. To guide food-bearing parents to the spot, the fledglings then set up a plaintive, insistent racket. The time of day, as well as the time of year, seems to influence birdsong. Different species sing at different times. Late in the afternoon, bird songs seem softer than at daybreak; dusk prompts the Vesper Sparrow to sing, while the Whippoorwill is vocal only at night Bird song travels best at night and therefore the few night songsters, like the nightingale, are perhaps our best known and loved singers. Singing stops when the nesting period is over.
There are 4000 species of songbirds, 300 species of hummingbirds and around 300 species of parrots all with different songs. From where do they get these songs? Scientists believe that birds are born with some innate auditory capacity to develop a song which is then modified and perfected as a result of practice and listening to older birds singing so birdsong is a mixture of pre-programmed knowledge of their species song and learning from older singing males.
Birds show definite learning skill; they sing a song that is a bit of mess at the beginning of their first season, but after a couple of weeks of practice become much better at singing the species' anthem. . There is much variation between species though. Some species cannot learn anything besides their own species song while others pick up whatever is available and even learn the song of other species. In fact imitating or mimicking the calls of other species is one way that birds can increase their own repertoire, and be more attractive to mates. Starlings for instance will copy the whistles of various shore birds as well as the sound of other songbirds, even mechanical sounds and incorporate them into their song. They have been known to mimic sheep and buses! The jay and catbird have a talent for imitating other birds' sounds, but the mockingbird tops the charts by continually mimicking not only the songs of other birds, but frogs and even noises such as sirens. The greatest song mimics though are the Marsh Warblers. Being a migratory species, they have an international repertoire that includes the calls of over 200 other bird species. The Lyrebird, in the forests in Australia, can imitate 12 other birds. It does the whirring of a camera's motor drive and the click of a shutter. It repeats the engine of a car, and the din of a car alarm. It can even imitate the screech of the chainsaw wielded by the loggers coming to cut down its habitat.
Even in the same species, just like us, birds too have regional dialects. In fact females tend to prefer males who sing in the local dialect. This is even truer of non-migratory species. So based on their song, bird watchers can actually place birds within a couple of miles of their home range.
Popular logic would have it that since the size of its brain has to be small; birds cannot be very bright creatures. Yet here you have all these birds making all these different songs in a very, very precise way, learning new songs varying volume, tempo, pattern, rhythm and pitch, plus phrases and numbers of notes, and then using each song depending on the purpose, season and the territory. How did they get to be such clever, creative and enormously gifted creatures? Next time you’re tempted to call someone a birdbrain, remember you might actually be giving them much more credit than you intend.