New birds by the hedge-load

The acre's maze of windbreak hedges leaves plenty of room for surprise. Walking out softly in the morning, I confront in peace any number of fresh-minted birds: the first human of their lives. A different story, of course, if Meg gets out before me, bounding ahead like a small, black leopard: her progress triggers blackbird alarm calls all the way down the path. What do you do when you find your pup playing with a fluttering, speckled fledgling, like a cat with a mouse? Let out a futile roar that can be heard across the townland ("Viney's dog is at the birds again!").

I sneak away from her, some evenings (she watches television), to enjoy the scent of the old shrub roses, the flush of light on the mountain, the deepening blue of the sea. An innocence settles on the acre, and my long shadow merges with all the others. A brood of little hedge-sparrows gathers on the ground beneath their nest, wings whirring as they beg for food. Young chaffinches sift suddenly into the oak leaves beside me, exchanging bright glances. A song thrush hops out into a patch of sunlit grass: a showroom model with polished beak and gilded feathers.

Such a multiplication of birds! The extra numbers will catch my eye for the rest of the summer: wrens in family parties, rummaging after spiders like packs of little mice; tits and willow warblers working the insects in the spruce trees, several storeys at once, like office window-cleaners; blackbirds in half dozens at the blackcurrant bushes, dragging down the branches with their weight.

Some birds have a more domestic start in life than others, enjoying weeks of dependence and a lot of free meals on the way to fending for themselves. Young rooks, for example, stay with their parents for about two months; young ravens drift around with their parents through much of the summer, and may eventually have to be driven away from the family territory.

Among songbirds, which often raise two or three broods in a summer, there is less time for infancy: robins, chaffinches and blackbirds, for example, all stop feeding their young about three weeks after fledging. The poor starling fledgling, by contrast, blinking in the light outside its nest-hole, gets only 10 days or so in which to learn how to feed or spot danger. This is the time when so many starve to death, fall into ponds, hit windows or smack into a windscreen. And then, as if to celebrate being alive, the surviving juvenile birds gang up into flocks of their own and wheel away to the nearest open moorland or estuary, there to practise formation-flying (my theory, anyway, having flinched away from so many sudden whooshes across the hedge).

Unlike the regular migrants, such as swallows and warblers, or those driven by extremes of winter weather, such as the Continental thrushes, many of our resident songsters remain very local birds.

Juvenile chaffinches, for example, gather into little groups to moult their first feathers, moving away for several kilometres, but most settle again to a particular area and stay put for the rest of their lives. In winter, when migrant chaffinches pour in from Scandinavia, our "locals" are the ones feeding near the hedge or at the edge of the wood, while the foreigners feed in large flocks out in the middle of the fields.

Irish wrens rarely wander more than 10 km, and our robins are likely to be even more sedentary than those of the UK. In one British study of 90 ringed robin nestlings, only a dozen ended their lives more than 8 km away. In another big study, of ringed nestling blackbirds, no fewer than 93 per cent were recovered in later breeding seasons within 8 km of their birthplace.

The upsurge in countryside bird numbers, suddenly obvious when the first fledglings start tumbling out on to the lawn, can seem almost to melt away later on in the summer. Cock birds leave their singing-posts and both parents, rid of their young in late June or July, become more discreet as they go into moult; everything falls quiet.

In this muffled interregnum, the notion of young birds moving "away" can blur the fact that some of the young from there have now moved here. How far can any piece of countryside absorb one summer's natural increase?

Cape Clear island, off West Cork, is one of the most intensively studied bird habitats in Ireland. In 1965, a total of 160 pairs of robins was counted there, with a concentration in the sheltered, bracken-covered valley that runs through the centre of the island. In 1986, no fewer than 410 pairs were counted - an astonishing increase among such an aggressive and territorial species.

This certainly showed the fluctuation that can arise quite naturally in a local population of a species. But even at its most "elastic", the countryside cannot find room for the hosts of chicks hatched out each year. In a rule of nature that only humans defy, if a population is to remain stable, the number that die each year must equal the number born.

Thus, if a pair of tits raise 10 young, this is the number that must die, somewhere, within the year. In rough terms, one of the adult pair will survive another year and so will one fledgling. On average (with all the exceptions that entails), nearly three-quarters of juvenile robins alive on August 1st die before a year has elapsed. Other Irish songbirds can expect to live rather longer: a song-thrush for about a year-and-a-half, a blackbird for nearly two years, a chaffinch for two-and-a-half.

This harsh actuarial table does something to ease my conscience when Meg insists on dragging a squawking blackbird infant from the depths of the hedge and batting it from paw to paw. Something - but not much.