The joy of such harmonious madness

Another Life: A day or two before Old Nature struck back with a properly stormy start to March, a snatch of spring song from a deluded skylark drifted up from the dunes.

It was all of a piece with dysfunctional thrushes lauding the January sunrise and robins switching into a major key when they should still have been singing sotto voce. I am losing the courage for phenology, the dating of natural events, feeling it too much like charting the progress of a plague. But when a bird sings beautifully at any time, I stop and listen, existentially. Like Shelley:

Teach me half the gladness

That thy brain must know,

Such harmonious madness

From my lips would flow,

The world should listen then, as I am

listening now.

The poets are just a tap away on the web these days and there's even a tantalising, seven-second snatch of skylark (at www.wildsong.demon.co.uk/BA/Songrm2.html) to give you the real-life sound of the scribbled skylark sonogram on view. You can slow the recording down to a 12th of the proper speed (like a clarinet playing the blues) to separate the notes - birds having, it's suggested, 10 times our ability to distinguish the individual shards of music.

How, indeed, does a bird utter such complex cascades of song without seeming to draw breath? Its vocal organ, the syrinx, is a bony structure at the bottom of the windpipe (our larynx, or soundbox is at the top). That gives it separate access to each lung, with separate membranes making separate sounds to feed into its throat, enabling some birds to sing two notes at once.

The secret of non-stop delivery is a rapid run of shallow mini-breaths, one for each syllable.

Since the first attempt to show birdsong in its musical notation, in 1650, its precise sounds have driven poets and professors to reckless equivalence, though this, from a Dr Walter Garstang, seems a pretty good stab at the skylark's opening chorus: "Seww! Swee! Swee! Swee!Zwee-o Zwee-o! Zwee-o! Zwee-o!Sis-is-is-Swee! Sis-is-is-Swee! Joo! Joo! Joo! Joo!" (If you're on the Dart, wait till you get home.)

Reading this kind of transcription, however, can reinforce the idea that, having learned it once in the nest - and most male birds do seem to learn from their fathers, rather than coming hard-wired for utterance - there's an unchanging song for each species. This may be true for the poor chiff-chaff, repeating its disyllabic tocsin of spring. Even the cock chaffinch, with its fine little descant of notes and a final, hiccuping flourish, is doomed to repeat it note for note more than 3,000 times a day, or half a million times a season.

But an individual song-thrush has about 100 different phrases to draw upon, each widely ranging in pitch, timbre and emphasis, and may repeat itself, allegedly, only twice in 85 phrases ("Lest you should think," in Browning's inevitable lines, "he never could recapture/ The first fine careless rapture!") I can't confirm this, seeming always to start listening in the middle and having something else to do before the end.

That sort of performance may be further enriched by phrases borrowed from neighbouring birds. A warbler I shall wait for later in the spring is one whose ratchety voice rings out across the vegetable plot long before I find him with the glasses: an otherwise nondescript little brown bird singled out by a stripe above the eye.

The sedge warbler is famous for his repertoire, mixing as many as 50 phrases in long streams of song, almost never repeating himself in a run of perhaps two minutes. Among his jumbled syllables are often quick lifts from other birds - chaffinch, linnet, blue-tit, sparrow - rattled off as if proving an extra accomplishment in his lonely-heart ads for a mate. Other birds will appropriate even quite alien musical sounds: the starling also is notorious for this, borrowing from sheep, tractors or mobile phones.

Such facility has encouraged some researchers to talk of a "cultural evolution" in birdsong and the possible use of "grammar" in their orations from the tree-top. This is heavy stuff, reaching for linguistic theories devised by Noam Chomsky, of all people, whose scientific day job has been quite eclipsed by his politics.

Equipped with the "Chomsky hierarchy of grammar", one American recorded 44 sparrow-sized house finches, singing up to 100-odd songs each in 18 far-separated suburban neighbourhoods, in the hope of detecting the use of "a grammatically constrained, stochastic song generation procedure". But it was no use, apparently: you'd have to get inside their little brains.