How Fidel Castro came to life on a remote Scottish island

The helicopter was on its way back from the Isle of Coll, one blue afternoon this summer, when we saw the dead whale. At first it might have been a white boat, capsized. But the shape was wrong: a bulbous oval ending in a tapering point - much like the helicopter itself. We came down to within a few feet of the sea and hovered.

It was an adult humpback, some 40ft long, floating on its back with its tail flukes trailing under the water. Already swollen with decay, it bore no sign of injury. This whale seemed to have died of natural causes, disease or just old age. It had drifted into the narrow sound between Mull and the island of Inch Kenneth, and at any moment - probably the next tide - it would be washed up on the shore.

There it would become a problem - the sort of problem that islanders encounter. Once, a dead whale was an opportunity. Men and women with knives, at first flint and then iron, would race down to the shore and see what could be made of it; if the meat was too rotten to smoke or even to feed to dogs, there were the gigantic bones to make anything from the arches supporting a thatched roof to primitive shovels, foot-ploughs or even combs. All down the west coast, people sit in the sun outside their houses on stools made out of whales' backbones. Until a few years ago, my mother hid her door keys between one of these drum-shaped stools and the great bone disc which separated it from the next vertebra.

But a dead whale is no longer welcome these days. What's to be done with it, this helpless mountain of carrion delivered by the ocean? Environmental health officers are duly notified. But as they are busy men and women who usually live a day's journey or more away, there is not much they can do. If there is enough depth of soil or sand and somebody local has a giant bulldozer, the corpse can be buried. Those are big "if"s, on a rocky coast with few inhabitants.

On Lismore the other day, the military sent in engineers with explosives to cope with a whale, but all they did was spatter the landscape with lumps of putrid meat issuing an unimaginable stench. The islanders were vexed, but scarcely surprised. The Tourist Board, whose certified Area of Outstanding Natural Beauty (AONB) had suddenly become an unlicensed Civic Amenity Waste Disposal Point, went into mourning. The gulls and the crows celebrated.

If you live on an island, things and people come to you. The island is a stage and the islander forms a natural audience, always prepared to appreciate the flotsam, jetsam and visitors washed up there. When I was a boy, spending a good deal of time on islands, scavenging was my main activity. I applauded everything the sea brought me, from lumps of paraffin wax and timber hatchcovers to Caribbean nuts brought by the Gulf Stream and bales of latex or kapok. And it follows that human arrivals on an island, finding such a stage and audience ready for them, act out their feelings, like members of a travelling theatre company, with special zest.

When we saw the whale, I had been out to Coll to see just such a use of an island as a stage. It seemed to me at first eccentric that Coll should have been chosen as the base for a youth volunteer project that sends young people out to work for a year in a Third World country. I had known the island well when young; it is rough and a long journey from any city. But Coll turned out to make sense as the nucleus of "Project Venture" for two reasons.

The first is what remains of its crofting economy. Major Nicholas Maclean Bristol, the project's founder, insists that nobody can hope to get the sense of a peasant society without understanding subsistence agriculture; the school-leaver volunteers start their training by living with local crofters for a week or so. But the second Coll advantage is the dramatic impulse, the sense of island-as-stage.

The day I was there, four groups of volunteers had just returned from a year spent in Cuba, Brazil, China or Vietnam. Jet-lagged, they were also in degrees of psychic shock: the re-entry into Western abundance, the fall in political pressure, the parting from friends and lovers. So almost the first thing they did was act - wild and funny improvised pantomimes of a Fidel speech in Havana, a ticket-queue in Canton station, a university tea-party under the bust of Ho Chi Minh, a Brazilian dance.

It was a rite of homecoming. There were other things to do before they returned to their real homes in Somerset or Manchester or East Lothian: debriefing about their work conducted by the regional "desk officers", a health check, a discussion about the recruitment of fresh volunteers. But the enacting, with all its release of tensions and its undercurrent of farewell to comrades who had shared the experience, was the centre of it all. They came off the planes and boats, bursting into the silence of Coll and into the project headquarters built a few yards from the Atlantic shore, and gave - in both senses - the performance of their lives.

A friend of mine, the diplomat Iain Orr, is at work assembling a computerised global database of all the world's islands. If he can raise the finance, it could be ready in a few years' time. The "Islands 2,000" inventory will contain not only the names and natures and contents of islands but details of what they have meant to the writers, scientists and explorers who have visited them. This is a dream that deserves to succeed, because Orr is convinced that the specialness of islands has not yet been understood.

"Hard to reach" is what islands are not. It may take a voyage for humans to get there but a multitude of things reach an island, from dead whales to freighters loaded with whisky to butterflies blown by freak winds across a hemisphere of ocean. In comparison, almost nothing "reaches" a city doorstep except milk and newspapers. An island, in short, is exposed to all the phenomena, living and not-living, that move on the planet and by moving compose what we call "life".

It was this feeling of entering small worlds ruled by chance that pleased Samuel Johnson and James Boswell when they toured the Hebrides two centuries ago. Their very arrival in Coll was an accident, a run for shelter in a sailing boat hit by autumn storms. There they met Donald Maclean, "young Coll", whom Johnson called "as complete an islander as mortality can figure ... He is hospitable and has an intrepidity of talk, whether he understands the subject or not." And Johnson, realising that on Coll he rated as a fascinating bit of human jetsam himself, let off his intellectual fireworks in special performances for the islanders. For him, too, the island was irresistibly a stage.

When we had done with the whale, the helicopter rose high to cross the mountains of Mull. Beyond lay more sea, more islands. The sea sparkled around them and then, under the Prussian-blue stripe of a tidal current, I saw another huge creature moving slowly beneath the surface. It was too far off to see what it was. But it was alive, and the islands lay in its path.