Trying to keep track of our winter visitors

Another Life: Two late arrivals for our autumn assembly of whooper swans flew in low along the shore from the north.

They stretched out like great white bombers - dambusters, even - but had two darkly-puzzling Spitfires in close attendance. As they touched down together on grass beside the strand, the escorts were identified (by an astonished David Cabot) as a pink-footed goose and a barnacle goose, neither much more than a quarter the size of the swans.

What strange consensus could have drawn these birds together for the flight south from Iceland? The whoopers were starting out from their breeding grounds. But the pink-foot and the barnacle had already crossed from east Greenland, each in its separate migrating flock, and were merely stopping off in Iceland for rest and recuperation. Neither goose had any business heading for a winter at Thallabawn, yet both remain here, grazing in the fields at the shore or floating on the lakes, still in company with their giant minders. Could they think they are whoopers?

This pleasing oddity has echoes at the Wexford Slobs, Ireland's best-known wintering wildfowl reserve. Here, among perhaps 8,000 Greenland white-fronted geese, there are usually a few wandering pink-feet, barnacles and Canada geese - even, most winters, the odd snow goose from North America. And as the tide covers the sands of Wexford Harbour, dark and dapper little brent geese (pictured) from the High Arctic Islands move up onto the fields to join them.

As migrant wildfowl and waders settle in across Ireland, worries about bird flu are bound to prompt unusual curiosity about which species come from where. Answers are offered, in passing, in a hefty tome just published by BirdWatch Ireland. Edited by Olivia Crowe and priced at €35, Ireland's Wetlands and their Waterbirds: Status and Distribution uses surveys covering all of Ireland in which a small army of observers, amateur and professional, out in all weathers for seven winters, counted the birds at chilly coasts, lakes and wetlands. Whoopers and sanderlings, shovelers and snipe, they've all been computed, their fortunes told, their habitats ranked in importance for care and conservation.

In the species profiles, migratory origins are part of the story. And while most of our winter geese belong to distinct populations with straightforward seasonal transfers between the Arctic and Ireland, the picture grows more complex when it comes to ducks and waders. Mallard, for example, are our commonest and most widespread winter duck. Migrants double our population to some 84,000, counted at 466 wetlands. They could have come from Scandinavia, Russia, Poland, Denmark, Germany, Netherlands, France or Belgium.

Wigeon come from Iceland - but also western Europe. Indeed, there are five wigeon populations breeding across northern Europe, with separate migrations to Asia and Africa. Our 56,000 winter teal could have come from as far east as Russia, and the cold winter we are promised could send them on to Spain as part of a great convergence of ducks from all over the Continent. Even Ireland's resident and colourful shelduck have a seasonal migration - an autumn moult at Helgoland Bight on the Wadden Sea, where they mix with shelduck from Scandinavia and the Baltic.

Our coastal waders generally nest in the far north (most golden plover and black-tailed godwit from Iceland and the Faroe Islands; turnstones from as far as the barrens of Arctic Canada). But the inland species have mixed origins and some are impossible to count in the wild. Snipe, for example, are likely to have come from the Faroes, Iceland or northern Scotland, but cold can drive them all the way from Poland. Woodcock start from Scandinavia and Russia. Lapwing from central Europe boost Ireland's winter flocks to around 200,000.

Such vast flocks, such diverse origins and interminglings, convey the futility of taking up arms against migrant birds with any prophylactic intent. It may be lucky the kinds of large, grazing (and defecating) wildfowl most likely to have encountered H5N1 and to carry the risk of passing it on to free-range poultry come to Ireland from the highly sanitary Arctic. Even Bewick's swan, the eastern European bird that used to reach us in thousands, has lately declined to a few hundred visitors, being largely waylaid in Britain by all the free food at wildfowl refuges.

Meanwhile, last week's splendid documentary on BBC1, Supergoose, completed the story of brent goose migration the team had begun in the spring. The return of Resolute to Strangford Lough, transmitter stilled at last, caught the epic reality of one of nature's most adventurous lifestyles.