Shattered silence

Silence, autumn's great gift to the west, has been slow to settle in. In some years, the quenching of holiday traffic has seemed almost shockingly abrupt, an overnight flight of the summer people as if from a hurricane warning. This September's transition took its time, blurred at the end by equinoctial gusts, trees thrashing about, rocks rumbling, streams surging off the hill.

Then, a Monday and sudden quiet. The school bus came and went at 9 a.m., the post van paused at 1 p.m. A curlew spoke on the shore; ravens nudged each other overhead, trying for echoes; a hammer sounded, three farms away. My own spade scrunched into the soil, flipping out potatoes that fell with a dry percussion.

So this is not a dead silence: nothing as awesome as the clenched emptiness of the Arctic ahead of the summer thaw. Even without wind, Thallabawn rustles and mutters; the ocean gossips all the way to the horizon. The silence is companionable, even telepathic, offering to share the thoughts of fieldmice, hares, dolphins.

Midsummer, by comparison, brought unprecedented bedlam; the hillside roared with engines. For silage-making, yes, but also excavating, rock-loading, sand-shifting, block-hauling - contractors working sunrise to dusk to pay for their outsize, overpowered new toys. And then, across the pale, shaven fields, the stench of slurry-spreading. Through all of this filtered the tourist traffic, windows wound tight against the scents and sounds of an Irish summer.

Sometimes, when I am cowering behind our hedges and wishing July and August gone, I wonder just how peaceful the countryside really was in the 1930s, say, when I was born.

Perhaps horses and carts kicked up a terrible racket on stony roads. Perhaps the sound of one hand bashing in the village smithy was quite nerve-wracking, and the countryside a cacophony of braying donkeys, crowing roosters, whinneying mares. People's voices were louder and less inhibited, and there must have been a never-ending banging and clattering as things were made or mended out of doors.

Some of this comes across in The Young Haymakers, an engaging memoir of a farm boyhood in Offaly just published by Tom Murray, now 72 and living in Dublin. Even in 1938 there was plenty of mechanical noise - the drone of the horse-drawn reaper-and-binder, the clanking convulsions of the threshing machine. Museum-pieces of farm equipment serve Murray's keen nostalgia, but so does the everyday wildlife now shut out by the tractor-man's earmuffs. The clamour of nesting rooks in March is the one sound recalled in "decibels".

How indifferent are the birds to the modern noise created by humans? Research in the Netherlands has shown that the continuous roar of traffic from a really busy road disrupts their breeding success. In woodlands - Glen o' the Downs in Co Wicklow comes to mind - willow warblers were affected up to 1.5 km away by a road carrying 10,000 vehicles a day, and the impact got worse as that number increased or speeds went up past 100 kph. When birds can't hear each other sing, their territorial and breeding behaviour goes haywire.

Birds have a simple, single-boned ear, the hole covered by feathers, with low-frequency hearing useful for picking up stalking predators, and a high-frequency band tuned to sorting out the rapid sequences of songs. Our own ears are far more complex and act as wide-band, general-purpose receivers. They depend, in particular, on three tiny bones of the middle ear which act as a series of levers to conduct and concentrate the sound waves as they travel from the eardrum to the brain.

EVOLUTIONARY biologists can get quite lyrical about the way these three little bones - the hammer, anvil and stirrup (from their shapes) - were taken from organs originally useful for other things and assembled into the apparently perfect organ of the ear.

The bones' evolution began in fish, which "hear" mainly by picking up sound waves through receptors along their lateral line. They started out in the gill-arches of primitive fish, were copied into the hinged jaws of reptiles and then, in mammals, were articulated and refined to conduct sound as vibration.

The hearing of humans may not reach into the higher registers, above 20 kiloherz, that cats, dogs and monkeys can perceive, but it is still incredibly sensitive. Sound is made up of rapid and minute changes in pressure in the air, travelling outwards in waves, and in the range of human hearing from detection to the threshold of pain is 120 decibels, a ratio of pressures of 1:1,000,000.

Most sounds that matter biologically are made by living creatures themselves. Crickets may be tone-deaf, but can read each other's chirps for courtship or aggression. A moth, with two cells' worth of hearing behind its eardrums, can detect the ultrasonic cries from a bat and make a power-dive to escape. Only humans generate sound with no purpose - incidental, brutal, mechanical sound that males, in particular, seem to relish: snarl of motor-bike, whine of chain-saw, the stridor of Formula 1. Amplified rock groups now outstrip male howler monkeys, whose roars reach out a mere kilometre.

Human young have conditioned themselves to tolerating pressures of sound unprecedented in history. (Not only the young: the average shoulder-to-shoulder champagne reception would have me fleeing into the night).

As yet, we have no real idea how modern human sound pollution is impinging on the rest of nature: wild species tend to hear what is important to them and filter out everything else. Birdsong drowned out by the motorways is one indication of what sheer, sustained volume can do. The acoustic world of whales and dolphins is disrupted by marine engines and seismic bangs. Even rats, forced to listen to human music, choose Mozart over Schoenberg.

Here on a tangled acre, among windfall apples and shredded fuchsia flowers, a singing robin makes all the sound there is.

The Young Haymakers (price £6.99) is published by Kimleigh Books, 53 St Assam's Park, Raheny, Dublin 5

A Wildlife Narrative, compiled from ten years of this Michael Viney's Eye on Nature column is now available at £9.99 from book shops and from Irish Times Books, fax: 353-1-6718446