A Highland army of volunteers mounted guard on an eyrie to protect a new generation from predators. Jim Crumley watches the results
There is only snow to lighten a winter day on the Highland Edge. The glen, one of the southernmost mountain realms of the Highlands, has a kind of upper chamber where the snow lies flimsy and wet and half-hearted. But up on the heathery rocks of the rim, there is snow of serious intent. These last few hours of afternoon twilight, I have watched it thicken, seen the rim harden.

I have come to look for golden eagles, two at least, three perhaps, and to add a crucial postscript to a remarkable eagle year in this glen. But in the past four hours, nothing has moved. Nature gives a fair impression of absence. Had it not been for an intimate acquaintance with the glen in its more fruitful seasons as well as its past winters, I could be forgiven for thinking that this grey-white desert had nothing to offer a nature writer like myself.

In such a place on such a day, when only your mind is moving, the phrase "looking for eagles" acquires a preposterous tinge. They could be anywhere within a 20-mile radius, for golden eagles grow markedly relaxed about territorial boundaries in autumn and winter. If they are anywhere else within this territory today, it proves nothing at all, but if they turn up in the glen, then I will go home celebrating.

Eagle nest sites are traditional. Usually an established pair will use three or four eyries in the heart of their territory for as many as 20 years. This pair is typical. What is not typical is that before 1995 their eyrie had been robbed every year in the last eight.

Eagles produce extreme reactions in people. To a wanderer of Highland landscapes there is no more throat-tightening thrill than a flat-out 100mph eagle contouring your crag and taking you in side-headed as her orange eye blurs past. To a hill farmer, the very presence of a lock of wool on an eyrie brands her a lamb-slayer. To the egg-collector, a clutch of two newly-laid golden eagle eggs is gold dust. When the pair consistently produces eggs of unblemished white like this one, they are even better than gold dust.

Last year, I witnessed one more extreme response, the like of which no Highland glen or golden eagle has ever witnessed before: a mustered army of eagle protectors. What began as a determined conversation last winter among a handful of conservationists and professional naturalists grew wings of its own and astounded us all. A decision was taken at that first meeting to mount a watch for as long as possible, as often as possible, through the crucial spring weeks of incubation and fledging (there is a lesser trade in young birds) in an effort to thwart the robbers.

There was reasonable optimism. Perhaps 20 or 30 people might be found to undertake seven-hour shifts through the tail of winter, spring, and early summer, armed with walkie-talkies and making their presence known to potential thieves. In fact, more than 100 people turned out, some just once but many again and again. No one was paid a penny, either for time or travelling expenses or anything else. There were turn-outs from the RSPB, the Army and the police, but the great mass were local people, rallying to the cause of golden eagles.

Such devotion to wildest nature is not the image Highland people like to paint of themselves, as anyone who has sat in on, say, a public meeting to discuss the proposed funicular railway on Cairngorm might quickly discern. Muttered oaths with the word "eagle" at the end and variations on the theme of "you can't eat scenery" are what many vested interests would have you believe is the norm. But the bond between Highlander and Highlands goes deeper than many a Highlander cares to acknowledge. Now and again he gives himself away and musters an army to fight for eagles.

Well, it worked here. The glen bore a new generation of eagles for the first time in almost a decade, and because of the number of volunteer eagle-watchers, no attempt was made on the nest. In July, two eagles about 12 weeks old flew from a high, dark and overhung ledge, and long before an official-ish party was thrown for the watchers, many a hipflask was uncorked in the glen and tilted toward the eyrie to wish them well.

The successful fledging of twin eaglets is comparatively rare, for the smaller of the two often succumbs to the sustained bullying of the stronger one, particularly if prey is difficult to come by. But these adults proved supreme hunters and parents par excellence, and in that most benign of all summers the larger chick's bullying amounted to nothing more than a pointed explanation of the rules of the pecking order.

The eaglets drift away eventually, often in the autumn, occasionally as late as December. I last saw three birds together in October, a few days before a young and partly decomposed eagle was found a few miles away. The survival through the first winter of both birds was too unlikely to hope for.

So my purpose in the glen at the year's end is twofold. One is to try to establish the continued well-being of the surviving eaglet. A young eagle is identifiable even at a distance by white patches on the undersides of each wing, individual birds (if you know them well enough) by the shape of the patches. My second purpose is to see if the adults are together in the glen and close to one of their eyrie sites. Even now, with the Highland Edge daylight down to half a dozen usable hours, the long ritual of golden eagle pair-bonding and eyrie selection can begin at any time.

There is no more heady confirmation of nature's commitment to a new life cycle than the scrawled free-falling signature of golden eagle display flight devouring the glen's January skies in 1,000ft gulps, beating and soaring 3,000ft above the summits to flip over and wing-fold and fall again. It is only a few weeks away, and after the past year in this eagle glen, it will be a more telling moment than ever.

But now, after four bleak hours, there has been no hint of eagle or any other living thing. In the last two hours of daylight I decide to climb to the rim and to the glen's headwall where there are wider fields of vision across tumultuous high moors and summits.

The light on the rim is paltry. The snow falls in fits and squalls and it stings. I have paused in the lee of a cairn, my eye fixed on a vivid white splash on a dark patch of rocky moor. Not snow. Not quartz. Not sheep. Snow fizzes into the lenses of the binoculars, rendering them all but useless. Then it moves. An ungainly flop, backwards. Then it is suddenly airborne. It is a dead mountain hare and it is slung under the moor-coloured bulk of an eagle.

It was all the day offered. Confirmation is a mighty reward for the day's endeavours. It is one more truism of nature in these parts that when the golden eagle is in good heart the land is in good heart. But in much of the Highlands it is all too precariously poised, and so is too much of the land.

Too many hands are still turned against the bird. Too many still die from the most unnatural of causes. But in one glen on the southern edge of the Highlands the cause of eagles has taken a small step forward. That glimpse of the slung hare is a symbol of the continuity, quite possibly thousands of years of it, of eagle life in the glen. It will soon be time to muster the army again.

The writer is author of 12 books on the landscape and wildlife of Scotland.