Those House Martins which so skilfully built their mud cup nests on your gable wall, and the Whitethroats which gabbled so cheerily down your lane, where are they now? It's a good question, with Spring in the offing and millions of migrants ready to pour into Britain like an invading host, but with no more hostile intent than to pair and raise their young.

With a little careful calculation you really could make a reasonable shot at pinpointing their present position. Travelling at more than 100 miles a day, flying by night and resting and feeding by day, they have already made big inroads into the 6,000 miles many of them will cover from deep down in the African continent before they pitch down into the English countryside.

Not only Martins and Whitethroats, but countless thousands perhaps millions of warblers, swallows, flycatchers, redstarts, cuckoos and turtle doves achieve the same fantastic journey.

They safeguard themselves against the main hazard of starvation, which is the threat in all such feats, by keeping behind the isotherm that quickens the insect world into life, and so making sure of sustenance on the long flight.

If the weather stays cold, as it has in the past few Springs, they hang back till the warm belt resumes it's northern march and they can fall in behind it.

But when this happens they are late in arriving and disappointment is acute among those who look forward eagerly to their return. I remember one early April day a year or two ago, after cruising in the Mediterranean we called at Casablanca and found a vast concourse of migrants swarming in the air and in the bushes clearly stalling in fear of bad weather ahead.

It was the year the spring turned sour on us. We beat the Swallows back to England by nearly three weeks, and it was not until well into May that the swifts arrived in numbers. Let us hope it will not happen this time.

In only a few weeks time, if all goes well, the woods of Delamere Forest, Alderley Edge and the hedgerows of the Cheshire countryside will echo to the delicate minstrelsy of the willow warbler.

The monotonous bi-syllabic refrain of the chiffchaff, the sand martins and swallows will be hawking over inland waters taking the ambient insects before they disperse to their breeding sites.

On the moors, the first of all the invaders, the wheatear will be flicking his tail on tussock or fence as if he had never been away, and one day the lovely yellow wagtails will come down in a flash of dazzling colour on the muddy margins of Sandbatch flash.

The voice of the feathered songsters will be loud in the land, and hurrah, spring will have come.