The moor, the merrier: Shooters, beaters and landowners are all in thrall to the 'mystique of grouse'

• A dog bags a kill at the Burnfoot estate. Pic: Greg MacVean

He points his stick at the purple heather which grows in beautiful profusion on the 12,000-acre estate. "That's our rainforest, that stuff there, man."

It is 13 August, the day after 'The Glorious Twelfth', when the grouse season began. It runs until 10 December, a four-month window in which keepers on Britain's moors are kept busy driving the small brown birds towards shooters who may have paid 1,500 each for the pleasure of attempting to kill them. And it is a pleasure. A privilege, too. That's how the shooters - or "guns" as they are known - describe it.

"I've not shot grouse for so long, I'm desperate to do it," says Andrew Durie of Durie, the patrician-looking chief of the Lowland family of that name. After he bags his first of the day, he is delighted. "Thank you very much," he says to the keeper who hands him the limp and bloody bird. "You don't know how satisfying that was."

It costs a lot to shoot on a grouse moor, but a great deal more to run it - an average of 150,000 each year. So although some estates in the north of England run as commercial businesses, in Scotland, where grouse are fewer, it's more about landowners maintaining a cherished tradition.

"There's not many places are viable as grouse moors," says Brown. "In Yorkshire, yes, but in Scotland we're just hanging on. This place of ours runs at a massive deficit. If it wasn't for the love and the passion for grouse shooting, this would all be covered with sheep or forest."

Brown is an interesting man. Patriot, Burnsian and advocate for the countryside, he is 43 years old, stocky, with silver hair and beard, dressed in tweed breeks and waistcoat. Keepers from different estates can be distinguished by the pattern of their tweeds. "It's like the clan system," he explains. Standing out on the moor, his right foot raised on a hillock of heather, his spaniel at his side, one arm holding aloft a red flag, he resembles a Socialist Realist portrait come to life.

As well he might. Brown seems to take 'A Man's a Man for A' That' as his personal creed, and is not one to tug his forelock in the presence of the upper classes who come to shoot. For him, Lord James Percy is "Jim". The Duke of Bedford, meanwhile, is "Big Andy". Don't go getting the impression that he's some sort of class warrior, though. Mostly, he's just obsessed with grouse.

He estimates that there are between 1,500 and 1,800 grouse on the moor, of which he can recognise many by sight, and he works long hours to ensure that they remain healthy and fruitful right up to the point where they are shot.It is, he grins, a paradox. He admires and respects grouse, and yet plans for and welcomes their death.

Grouse are entirely wild birds which eat heather and nest in it. They cannot be bred. Keepers try to increase their numbers by burning the heather in spring to promote new vigorous growth ("No bloom, no boom"), putting down medicated grit which staves off parasitic threadworms, and by slaughtering large numbers of predators such as foxes, stoats, weasels and crows.

The birds are baffling, though. Brown talks about "the mystique of grouse". Sometimes you do all you can to grow the population and it dwindles. Sometimes, like this year, the young grouse survive what everyone thought would be a killing winter.

Trying to get to the bottom of all this is partly what makes grouse such a fixation. Brown is the sort who has to be ordered to take a holiday, and he admits quite readily and regretfully that he spent little time with his two sons in their early years, leaving his wife Yvonne to do all the work. "I've almost lost my family over a head of grouse," he says, "and there's many an estate owner has spent their child's inheritance and gone through divorces over grouse. It just consumes you."

I was keen to understand this passion for myself, so had arranged to spend the day at Burnfoot. It's a beautiful area with an extraordinary view that includes both the Wallace Monument and the Forth Bridge. There is a wind farm on part of the estate, the turbines rising lighthouse-like from the moor. Hunting dogs continually vanish and resurface as they bound through the deep heather, bringing to mind dolphins breaching waves. Pollen rises like spray.

This isn't my first time on a grouse moor. Eighteen years ago, just before starting university, I worked for a few weeks as a beater on an estate in the Highlands.

Beaters are the infantry of a grouse shoot. They walk in a long, long line towards the guns, trying to scare the grouse up from the heather by cracking "flags" - often plastic feed bags attached to wooden poles. The movement of the line is monitored and controlled by the head keeper using a radio and phone, and signals are given by blasts on a horn.

I remember walking around 10 miles each day over rough and wet Highland terrain. You had to keep up. Stragglers were not tolerated. One particular keeper, a leering sadist in a deerstalker, had an especially effective method of motivating tired beaters - reaching down and grabbing you by the most tender parts.

Burnfoot isn't at all like that, but the work is still exhausting. As Brown puts it, "Grouse beating's like S&M in tweed."

But it has its consolations. You get paid for one thing. Not much, though. Forty quid for a day's work. Few, if any, of today's 30 beaters are in it for the money. Some are keepers from other estates who have agreed to lend a hand.Others have full-time jobs (there are loads of firemen and polis, for some reason) but spend their holidays working on the moor. A number simply relish the chance to give their dogs an opportunity to find and retrieve downed birds.

There is a festive, sunshiney air. Beer and spirits are offered at lunchtime. "Would you like a wee G&T?" asks Gary Boyd, 53, a broad-shouldered retired fireman from Grangemouth. He's working as a 'picker-up' and has blood on his shirt-cuffs. It's a real skill, noticing and remembering where the grouse fell. Picker-up is a job you earn after a long beating apprenticeship. Boyd has been at this for 30 years.

The guns lunch separately from the keepers and beaters. They are eating in a deep-green corrugated iron bothy. Walk in and you are hit with a hot smell of meat, wine and bonhomie.

There are ten guns shooting today - a well-to-do vision in tweed, gaiters and flat caps, cartridge belts sometimes slung below bellies. They are an interesting lot - farmers, businessmen, a couple of wealthy Americans who have flown here specially from Connecticut and are having the time of their lives. There's also Charlie Thorburn, from Perthshire, who was once a market trader but now breeds and trains hunting dogs. His clients include a Russian oligarch and a postman in Dundee.

Why is Thorburn here today? "Because I was invited," he says. "It's not necessarily about having money. I have some pretty wealthy friends in London who have been shooting all their lives and have never been on a driven grouse shoot. You basically have to know someone who owns a moor."

That someone is Nick Harvey-Miller. Having made a lot of money in the drinks industry, he became a co-owner of Burnfoot in 1990. A thick-set 56-year-old in a green tank-top, his hair worn longish, never far from a lit fag, he is good company and dryly ungenteel. "Don't shoot them up the arse," is his sage advice to his guests.

In fact, Harvey-Miller is a serious champion of grouse moors, arguing that they are economically important (a new report estimates shooting generates over 20 million each year for the Scottish economy) and that a properly managed estate promotes bioversity. He is proud of his birds - "One Scottish grouse is worth three English grouse any time of the week" - and seems pretty chuffed at his own extravagance.

"The heather moorlands in Scotland would disappear unless you had idiots like us who were willing to pump money into it," he beams. "Yet we're doing all this for perhaps eight days' shooting each year. There is an element of madness about it."

After lunch, I spend some time by the butts - the wooden screens over which the guns shoot. It's deafeningly loud and the smell of gunpowder fills the air. The grouse fly with a staccato whirr, travelling at up to 60mph and following the contours of the ground. They are considered the most difficult game birds to shoot.Those that are hit glide towards the ground with locked wings

By 5pm, the guns have bagged 141 birds. Traditionally, each shooter is given two to take home. The rest belong to the estate and are sold to a game dealer for prices varying between 5 and 12 per brace, depending on supply and demand.

For Brown, another day is over, but even as he drinks a valedictory lager, he's already thinking ahead. What will tomorrow bring? There's a lot of worry in his job, even though he loves it. Earlier, someone had asked him if he was feeling happy. "When was the last time you saw a happy grouse-keeper?" he replied. "You know when I'll be happy? The tenth of December when it's finished."