This has happened once already, early in the 19th century; but the species was re-established by a series of importations from Sweden, beginning in 1837, and the newcomers' descendants flourished so well in the central and eastern Highlands that they became a menace to forestry. In the course of feeding, they nipped so many buds and leading shoots from young trees that, to keep numbers down, gamekeepers smashed eggs and trampled chicks to death, and in winter landowners organised large-scale drives that often yielded bags of 100 birds in a day.
Today, the idea of such mass murder seems inconceivable, for although caper survived in quite good numbers until the Sixties, they have gone downhill ever since, and the most recent estimate suggests that there may now be fewer than 1,000 left in the whole of Scotland.
If the species does come through, its survival will be due in no small measure to the efforts of one man, Jimmy Oswald, who was head keeper on the Gentanar estate in Perthshire from 1968 to 1994, and in retirement has become a passionate advocate. His enthusiasm for caper has taken him to almost every corner of their range, from Scandinavia to the Pyrenees, from the Dolomites to the Carpathians, from the Alps to the Urals and the Altai.
In his early days at Glentanar, the estate held two caper shoots every winter and killed between 40 and 130 birds, most of which went to taxidermists to be stuffed. If, in any one year, stocks seemed to be low, shooting was suspended. Then in the Seventies, with numbers obviously declining, shooting stopped, and the keepers began systematic research. With the help of Robert Moss, a specialist from the Institute of Terrestrial Ecology, they started to monitor a study area, using pointers to find chicks and tagging the ones they could catch. In a typical year they would tag about 40 and see maybe another 100, which eluded them by flying up into trees.
The picture now is utterly different. "We thought the birds were doing poorly when they were at that level, in the Seventies," Jimmy says. "But two years ago, when we covered the same area using the same techniques, we saw one chick, which we caught and marked. Last year, after two weeks of bloody hard work, we never saw a chick at all. There are virtually none left."
Various factors are blamed for the decline, among them over-grazing by sheep and deer. This degrades the habitat, and in particular suppresses blaeberry plants, which caper need for food and shelter. Another damaging influence has been a series of late, cold springs; chicks have hatched before there is an abundance of the insects on which they depend for protein in the first few weeks of life.
Yet, in Jimmy's view, there is one villain whose destructive capacity far outweighs every other: the deer fence. For years keepers have been finding the remains of birds that have flown into the two-metre wire barriers built to protect forestry plantations, and now radio tracking has confirmed that the fences are major killers not only of capercaillie but also of black grouse. One researcher had five radio-carrying caper killed on fences in a single day.
The risks are particularly high in spring, for the birds are now homing in on their traditional leks, or mating-grounds. Once a dominant cock has established himself on an open patch at the edge of a forest, hens fly in from all quarters to court him, drawn by low-frequency calls that the human ear cannot detect, but which they can apparently pick up from a kilometre or so away. Gliding low along the glens in the half-light of dawn, with their minds on other things, they simply do not see the lethal obstructions in their path.
One estate on which caper are surviving reasonably well is Abernethy on Speyside, now owned by the Royal Society for the Protection of Birds. In the Eighties the RSPB took the courageous step of reducing the local red deer herd from 900 to 300, thus enabling the blaeberry and heather to grow luxuriantly, and over the past few years the society has removed 25 miles of deer fence. Further, between 1992 and 1997 the RSPB culled predators such as foxes and hooded crows.
These measures have undoubtedly helped caper to hang on at Abernethy. Other landowners are also taking down fences, but many, encouraged by government grants, are putting up miles of new ones in their efforts to keep deer out of selected areas so that they can regenerate the Caledonian pine forest of antiquity. Which are more important - trees or rare grouse? Conservation priorities are by no means easy to resolve.
What frustrates independent enthusiasts is the fact that so little positive action emanates from official sources. The name of the body in charge is daunting enough: the Capercaillie Species Action Plan Steering Group operates under the auspices of the Scottish Biodiversity Group, and those involved include Scottish Natural Heritage, the Institute of Terrestrial Ecology, the Forestry Commission, the Deer Commission for Scotland, the RSPB, the Game Conservancy Trust, the Scottish Landowners' Federation and the Highland Wildlife Park at Kincraig. In Jimmy's view, "all these people do at one committee meeting is decide when to hold the next".
He believes that immediate action is needed: stretches of fence known to be killers should be removed in the next few weeks, and measures taken to prevent members of the public disturbing the caper by wandering on to leks.
His own plan is clear: he has collected hundreds of signatures for a petition which he intends to deposit with the Scottish parliament as soon as it has been elected on 6 May. As he says, it would be a terrible shame if one of the first events of the new millennium, under a new regime, were the demise of a bird which in many ways has become the emblem of Scotland.