Flights of fancy: You can tell a lot about your garden by the birds that live there, says Anna Pavord. And you don't have to be a professional twitcher to enjoy them

Next weekend the Royal Society for the Protection of Birds launches its 28th Big Garden Birdwatch, an invitation to spy for an hour on the birds in your garden and record the most frequent visitors. Last year the survey involved 470,000 people who clocked eight million birds in 270,000 gardens. Being nice to birds is part of the national psyche. The number of people who belong to the RSPB (1,051,000 and rising) confirms that. In fact, we seem to be a great deal nicer to birds than they are to each other. Every day some battle rages outside our windows: a mob of small birds attack a hawk, sparrows brawl in the driveway, a magpie raids a nest, rooks dive-bomb gulls.

I'm not one of those million-plus RSPB members. Plants provide more than enough questions for my life, but I like birds being around me while I garden. The RSPB top 10 - sparrow, starling, blackbird, blue tit, chaffinch, greenfinch, collared dove, woodpigeon, great tit and robin - doesn't reflect what we see here. Rooks are by far our commonest bird, because they've made their rookery in the line of alders that winds along our boundary. We also have a lot of buzzards. Their cries, particularly the plaintive calls of the young when they are finally left to sort out their own breakfast and lunch, are perhaps the most dominant of all the bird noises in the valley. The problem with birds, though, is that you have such a short time to decide whether the blur that has flashed through the undergrowth has the red bit under the wing or the white bit under the throat that clinches its identity. Binoculars are not usually to hand when you are gardening. Even when I am not, I find that by the time I have got the things to my eyes and adjusted the focus, the bird has moved on half a mile and I am left casting around in the sky like a mad astronomer.

Voices help. I've learnt at last to pick out the sound of goldcrests, the smallest of all British birds (they weigh less than seven grams). They sing on a very high-pitched note, almost as high as a bat squeak. It is probably the yew trees that brought them to our garden. Goldcrests like yews and sling their nests like hammocks from the branches. A pair of them often work purposefully through an old pear tree, clearing out insects. That makes me feel extra welcoming towards goldcrests - I'd prefer they did the delousing job.

Mistle thrushes make a distinctive noise too, a loud, bossy sort of whistling - more building site than Brahms. But I like mistle thrushes. They are usually the first birds to break into song when it stops raining - a cheerful habit. And there's no way you can ignore the dik-dik noise that blackbirds make as dusk falls and they noisily announce they're going to bed.

Gradually, too, you begin to associate particular birds with particular things in the garden: plants that they raid for food, or places where they roost or nest. Dunnocks and wrens fiddle about on the ground in piles of leaves. Goldcrests like conifers. So do coal tits. Hawthorns attract hawfinches. Goldfinches favour thistles. I'm glad something does.

The amount of windfalls lying about probably accounts for the number of mistle thrushes in the garden. Fruit and berries are their preferred diet, like those other thrushy birds, redwings, that sweep in in autumn to feast on apples still lying in the grass.

Wrens are much in evidence. Or perhaps it's the same wren, extremely nifty on its feet. Wrens seem to like holes in walls, piles of brushwood, nothing too far off the ground, for their nesting sites. I sometimes find their nests, balls of moss mostly, wedged behind ivy on a retaining wall. The male apparently makes several and then takes the female round to show them off. Wrens fiddle around in the undergrowth, never high, feeding on insects. You can easily mistake them for mice.

The RSPB lists the wren as Britain's most numerous breeding bird, with an estimated 7.6m pairs spread through the UK. After that comes the house sparrow, though the average number in a garden (10 in the first Birdwatch survey in 1979) has crashed to four. Although they sit at number two on the top 10, numbers of starlings have decreased too, down from an average of 15 in a garden to three. Unfortunately the birds that are thriving, with massive increases in population, are the ones I don't like: collared dove, woodpigeon, magpie.

The collared dove was unknown in this country until 1955 when they were first recorded breeding in Norfolk. Perhaps it seemed exciting then, but numbers have now built up to pestilential proportions. The doves, smaller than wood pigeons, consume enough grain to feed the Horn of Africa.

Nesting sites in a garden are as important as food, I'm told by birder friends. A bird table may attract birds, but for them, it is like a meal in a restaurant. A home implies more complex requirements. 'Privacy, air, shelter from direct sun, and a nice orderly disorder' are what they are looking for according to E L Turner's Every Garden a Bird Sanctuary.

Some birds have a funny idea of privacy. One of the four nests in the wisteria on the front of our old house was built directly under our bedroom windowsill. A blackbird raised three babies here, undizzied by the regular swooping of the sash window, unconcerned by the proximity of the bodies that loomed up not more than a foot from her beak.

Disorder they have in quantity. I am glad that something is benefitting from the unraked leaves, the piles of unspread compost and stacks of uncut firewood that punctuate the garden. All these places swarm with insects - breakfast, lunch and tea. Ants, which created havoc on the lawn this summer, were probably the magnet for a pair of green woodpeckers.

Native plants are supposed to be the greatest asset for birds in a garden, though I notice birds feeding on a wide range of non-natives too. There's no doubt, though, that a hedge of Leyland cypress is an empty larder compared with the bursting possibilities of field maple, hazel, holly and hawthorn. If you have room, plant an oak, the preferred home of a thousand different insects.

Anything that fruits is good. In a small garden, a crab apple, an elder or a rowan would be my first choice. None of them takes up much room and all make a double contribution to the garden with blossom and fruit before eventually providing food for birds in winter.

Pyracantha and cotoneaster are obvious magnets for birds. Honeysuckle is also useful. Although we scarcely notice the berries, they provide food for warblers, thrushes and bullfinches. Thrushes also like the berries of ivy, which fills a food gap in late winter. Robins and blackcaps feed on them too, and the flowers attract a staggering number of insects, which in turn pull in different birds.

As for the rooks, my favourite birds, they come and go as they please. The RSPB records show that they appeared in the top 15 most common birds in the first Birdwatch survey in 1979. Now they've dropped off the radar. The Dutch elm disease of the Seventies and the massive storm of October 1987 decimated their rookeries. They are by far the most entertaining of the birds in the garden. I particularly like the way that, when you think they've settled in for the night, they suddenly lift off, all together, and whirl out in a display of flying skills that beats anything you'll ever see at Farnborough. And like the best kind of lodger, they take their meals elsewhere.

If you want to take part in the Big Garden Birdwatch, phone 0870 600 7108 or download a survey form from www.rspb.org.uk/birdwatch