The two notes that tell me spring is really here

The years advance and then they retreat. The days get longer and then they get shorter, and it's possible to see subtle changes on every one of them: changes that seem thrillingly optimistic in the spring and a touch grim in the autumn. You can pick up signs of spring in January or even earlier – I once heard a woodlark sing before Christmas – and you can feel autumn looming up in early August, usually on the day when you realise it's a week since you last saw a swift.

But some changes are more dramatic than others. It's a personal matter: for some people the first primrose changes everything – the name means prima rosa, the first rose of the year. Others rejoice when the wild plums throw out the first wild blossoms. Or perhaps it's the sight of birds with nesting material: a heron carrying what looks like a small branch back to base.

For me the greatest changes are announced in song and call: clear audible signals that sound as if a bird was giving permission for the seasons to change. In the autumn, the dark time of the year seems to be called into being by the gentle quacking of the fieldfares, thrushes that come here from Scandinavia for the colder months of the year.

And when the chiffchaff sings in March the whole year seems to change gear, put its foot down and race off towards the high spring. It's not a great song as songs go, but it's packed with meaning. The bird says its name again and again in rhythmic, repeating patterns. Each syllable is given an equal stress: if you hear a twin-syllable call with a strong stress on the first, it's a great tit -- and great birds though they are, they don't seem to me to change absolutely everything.

The thing about chiffchaffs is that they're the first migrants to arrive here and start singing. The songbirds that stay all year are mostly in full song by now: the great tits of course, chaffinches, dunnocks, and song thrushes and in the past fortnight or so, the blackbirds have begun their laidback fluty whistling.

But chiffchaffs mostly over-winter in southern Europe and northern Africa, so they have a distance to travel. As a result they start their songs a little later than the residents – bringing a new mood to the year. I should point out here that in these days of climate change, some chiffchaffs spend the winter here. If there's enough food to get them through the winter, it makes sense to cut out the hazards of that double journey. The early chiffchaffs I've been hearing this week may have been here all along.

But that doesn't diminish the drama. When the first chiffchaffs sing out, it's as if they're preparing the way for all the other more dramatic migratory birds whose arrival can no longer be greatly delayed.

The chiffchaffs fly in with two other two early arrivals. You might catch a wheatear hurrying north, often in some incongruous place like a playing field, flashing its white bum as it flies away from you. And as you look out over our watery places, you might catch an early sand martin or two swooping low over rivers and broads.

The chiffchaff seems to me like a herald with a two-syllable trumpet, gently but insistently calling the other migrant birds to their breeding grounds. He's summoning the swallows and swifts, the thrilling species of warblers – the tiny willow warbler commutes all the way from Southern Africa – the nightingales, and also the slim, dashing hobbies, falcons that will be with us just a few short months.

In mid-winter these birds seems like the desperate fantasies of a mind deluded by cold and darkness: but when the chiffchaff sings out we can start looking forward to their arrival with confidence.

Admittedly this is a confidence that gets slightly less robust with every passing year, but when the sun shines and the chiffchaffs sings out, it's possible to set such grim thoughts aside, at least for a while, and rejoice in what we've still got. So let's hear it: three chiffs – and three chaffs – for spring.