The barnacle goose is very clever, and was once, technically, a fish

he view, I thought, appeared much as it would to a young barnacle goose. I was diving out of a blustery, dove-grey sky, my wing tips tipping cloud. Far below I could see the browns and greens, the heather and grass, of a big, low-lying Hebridean island. To the east lay the Scottish mainland. From the west the ocean, whipped by a stiff breeze, drove tiny white horses on to long sandy shores. The Atlantic rollers were just visible beneath my wings.

But my wings were manufactured by Saab. Nose pressed to the window, I was aboard a 30-seater twin-prop passenger plane heading from Glasgow airport to the landing strip on the island of Islay. I would land there at ten in the morning on Monday, 13 October.

About 30,000 barnacle geese had landed just ahead of me this month. They had come from Greenland; I had come from Derby. My small voyage of discovery was the last of my adventures as the presenter of a five-part series for BBC Radio Four on migrating species called !Iloving On. My programme about eels has already been broadcast, as has my account of a feathered burrowdweller and transcontinental aviator, the Manx shearwater. The third and the fourth programmes, about migrating butterflies and basking sharks, will be broadcast at 2.45 p.m. over the coming Sundays.

Barnacle geese will be my fifth and final theme. Islay is winter home to about two thirds of the planet's entire population of Greenland-based geese (a separate tribe come from Siberia, wintering on the east coast of Scotland). This distinguishes them from most of Britain's other migrating species. Sensible animal tourists flee our winter, departing for sunnier climes. Islay's barnacle geese actually choose to come here in winter — for whatever the horrors of the Scottish climate, they are less horrific than winter in Greenland. Making his escape from his rocky nest in the subarctic ice (and flying en famille with his mate and the latest offspring), the bird finds in the Hebrides just about the first available landfall in the warm Gulf Stream.

The other is Iceland, which the geese use as a sort of pit stop en route, extending their break there whenever Iceland enjoys a warm September. The journey is more than 1,000 miles, and we have only patchy knowledge of how the birds navigate and how high they fly. The barnacle goose eats grass and little else. Having an inefficient digestive system, it cats a lot and almost continuously, choosing the tender tips of new grass growth. This puts the bird in direct competition with sheep and cattle, and does not endear barnacles (as they are called locally) to the Islay farming community. 'They've flown 1.000 miles from Greenland, one farmer told me. 'And it's only a few miles further over the water to Kintyre. There's lots of grass there. You'd think they could fly on for one last hop. But the buggers won't go.'

In fact, farmers on Islay have reached a sort of grumpy truce with the geese, mediated by ornithologists. Financial compensation for lost grass provides for reseeding, and now forms part of the backbone of the rural economy. Payments to farms of between 5_5,000 and £10,000 a year are not uncommon. A generation of crofters and farmers born to the assumption that their working lives would be spent raising mammals have now been told that their role is to keep out of the way of birds.

But still the geese have to be removed from newly seeded land. The island has an official goose-scarer. When I asked if he knew how to say boo to a goose, his weary glance suggested long acquaintance with the joke. His repertoire does not, in fact, include booing, but consists of a shedful of aluminium poles from which kites are dangled — to look like birds of prey. He also has loudspeakers, which emit strange noises. 'But they're canny birds,' he said. They recognise my Land-Rover. When they see me, they move to the next field. When I've gone, they move back.'

And this is about as far as they move. Winging its way across a whole wide ocean, the barnacle goose family often zeros in on exactly the field where the parents wintered last year — and stays thereabouts for the whole winter. 'They don't even take a fly-about to see the rest of the island,' a resident ornithologist, Malcolm Ogilvie, told me.

He told me, too, why the bird is named after a crustacean. Many centuries ago, the

feathery-looking interior of what is now called the goose-barnacle prompted an answer to the mystery of why tens of thousands of geese simply appeared in the Hebrides every autumn, apparently out of nowhere. They had hatched from barnacles, it was suggested. This made the bird, technically, a fish. 'Which could therefore be eaten by the God-fearing, even on Fridays,' smiled Malcolm Ogilvie. 'This may explain why the theory was not exposed to the critical scrutiny it deserved.' Only within most Spectator readers' lifetimes, and with Ogilvie's help, was Greenland identified as the provenance of the west-coasting goose and Siberia as that of the east-coasters.

Facts like these amuse and interest, but nothing could prepare me for the sight and sound of the geese gathering in their winter quarters.

Islay is not a spectacular island, but gentle, windy and wide, with low brown horizons and a high grey sky suffused with soft light. Everywhere is the buffet of the breeze and the whisper of the sea. Around the shore are littered a tangle of telegraph poles, the geometry of small straight tarmac strips going nowhere, and little cottages strewn over the landscape — like packing cases fallen off a pantechnicon, as D.H. Lawrence remarked of Western Australia in Kangaroo.

My producer, Jeremy Grange, met me at the airfield and we headed for the skyline on a ruler-straight road. 'There's some!' Jeremy exclaimed. We stopped. I got quietly out of the car as Jeremy reached for his tape recorder.

A whole wide flat meadow was speckled grey and cream as thousands of barnacle geese pecked furiously at the grass. The air was full of their ciy. The bird is smaller than a domestic goose and strikingly marked. The face looks like a pale-painted war-mask, the pate and neck are black, and the wings are a beautiful, partly striped grey.

Seeing us, the whole flock took flight. Their screech was everywhere. They filled the sky with a fluid swirl of black streaks, drifting and diving: a Hitchcockian nightmare.

And I don't know why — call me anthropomorphist — but it seemed to me that these birds were excited just to be there. The barnacles were on vacation. Each family included a member who had never visited before. Their winter holidays in Scotland were starting.

Matthew Pan-is is a political columnist of the Times.