Michael McCarthy: Real Spring starts this Sunday

I wrote recetly that four is not really a sufficient number for seasons, with mid-March, for example, being neither spring proper nor late winter, but something in between. And the spring's true heart also does not fit with the traditional versions. As far as I am concerned, spring in southern England, where I live, begins this Sunday, 15 April.

This is the date when conventionally, the cuckoo could first be heard in the Thames valley, and it also works, more or less, for first hearing a nightingale and first seeing a swallow. This avian trio, all migrating here to breed from wintering grounds in central, west and southern Africa respectively, are the supreme markers, by their arrival, of the springtime in Europe: all three of them are symbols of its advent in the folklore of every country of the continent.

And what begins with their arrival is a period of six weeks, let's say until about 1 June, when the natural world is at its most intensely alive. This is the time when birds are mating, which means they are loudly singing (to attract mates and defend territory); and then nesting, which means they are hunting in overdrive, to provide food for their chicks. It is the time when flowers bloom so that their colours can attract insects to pollinate them, and the time when insects emerge to mate in their turn. There is new life, birth and growth; there's frenetic activity everywhere, so that more wildlife is more visible in a world that is more beautiful than at any other moment.

And it's not just wildlife in these six weeks; it's the sudden reappearances of warblers and orchids and butterflies, the continuing pleasure of spotting the first this and the first that of the year. Some of the early swallows might be here now, but the first swifts won't arrive till the first week of May, and the first nightjars and spotted flycatchers won't be here till mid-May or even the end of the month.

Similarly with butterflies: the first orange tips are out now, dazzlingly handsome, to be followed by the first green hairstreaks and the first small coppers and then the first of the fritillaries, the pearl-bordered; similarly with wild flowers, the bluebells giving way to early purple orchids, and then the first cowslips, and then the first white starbursts of wild garlic.

It goes on and on, this brilliantly-coloured, fantastic procession of new life, until the cuckoos stop calling and the nightingales stop singing in early June; it's the spring proper, the best six weeks of the year, and (as far as I'm concerned) it starts on Sunday.