Why dawn?
Sound travels well in the cool, still air of dawn and the insect food of many species isn’t readily available yet; so it’s a good opportunity to spend time broadcasting a sound signal. Also for migrant males, females arrive over night: the early bird gets the mate. So virtually every male songbird sings for a long spell in the first hour of the day.

Why song?
Full song is all about males marking their territory and trying to attract and stimulate females - just like humans - putting on a big show, making a loud noise. Performing and competing with sound is less expensive and less damaging than fighting, though sometimes fights occur. Birds also have other ways of singing than just full territorial song: there’s the soft subsong of a male practising, excited courtship song in the presence of a female, communal song of a gathered flock of finches, synchronized duets between mates (we two are one) and more.

All a load of twittering?
As a general rule, the smaller the animal, the higher-pitched it’s voice. Songbirds are mostly very small creatures and have correspondingly high-pitched voices, with the result that their songs sound like whistles to our ears. Also birds’ hearing has a much finer temporal resolution than ours; so where we might hear a jumble of notes or a continuous trill or buzz, the birds themselves distinguish individual notes clearly. Slowing down a recording of bird song often reveals a fantastic hidden elaboration of melodic structure.

So it is a load of twittering?
Well yes, but not random and sometimes highly complex. Each species is different and with practice (and sometimes a computer) even each individual male can be recognised by idiosyncracies in its style or repertoire of phrases. Young males learn from their neighbours, so regional dialects develop. There’s often mimicry of other species, even car alarms, phone ringtones or other ’found sounds’. One of the most melodic singers is the common, garden blackbird; they even sound great in the centre of London with the reverberant acoustics of the tall buildings.

Music?
Before we had radio sing-along-while-you-work, it was common throughout Europe to keep songbirds in cages around the house for sound comfort. Mozart kept a pet Starling and learnt from its variation on themes; when the bird died he’s said to have held an elaborate funeral in its honour. In a world where we’re continually bombarded with cultural subtext, it can be very refreshing to listen to something that’s clearly musical, yet with no human signifcance.

Changing world
Dawn is still usually the quietest part of the day, though with our 24-hour lifestyles it’s now hard to find a place free from the background noise pollution of planes, cars, trains, boats, gas scarer-guns, refrigeration or air-conditioning units - mechanical noise. In Britain, environmental change has resulted in a diminished chorus over large areas, particularly in agricultural habitats. In the last 25 years the distinctive songs of many species have been lost as their numbers have declined: Corn Bunting by 86%, Linnet by 56%, Song Thrush by 57%, Tree Pipit by 77% ... (figures from the BTO).