A rich field for twitchers

The storms' revision of the strand has added an extra swerve to the channel that takes the mountain river to the sea. It now wanders the width of the strand before sidling into the breakers, and it makes a secluded lido for a flock of common gulls. I like to watch them against the low sun, flinging diamonds at each other as they bathe in the flow of fresh water.

They are irredeemably common: that is, of the species Larus canus. Really, I should prefer to call them "mew" gulls, as Americans do when the birds turn up by chance in Massachusetts: it is, after all, the sound they make. Down in Galway's docks the other day, I was startled by the yells of herring gulls, Larus argentatus. This is the common gull in harbours and rubbish dumps, but not at sandy beaches next to pastures full of earthworms, which is what L. canus is after at Thallabawn.

There is a great family of gull species: half-a-dozen kinds breed in Ireland and another 10 come visiting, mostly in winter - more if you start counting subspecies. The gulls are a rich field for twitchers, and this is the season for clocking up rarities as they wander in from the sea.

If I were to scrutinise every bird among the 300 or so common gulls as they splash about in the river, I might well see one or two that look a bit bigger and heavier, a bit paler on the back and with a broad, black ring on the bill. These are the ring-billed gulls, vagrants from America's east coast.

It's 20 years since the first ring-billed gulls were spotted in Ireland, at Belmullet in Co Mayo, and now they're counted as "regular but scarce". There has been a big expansion in the species in America, and enough are finding their way to Europe to take away the cachet of rarity.

But three other American gulls are still regarded as very rare vagrants to Ireland. Franklin's gull was first spotted in Co Kerry in 1993, a small, dark-mantled gull with burly wings and a sailor's rolling gait. The other two, the laughing gull and Bonaparte's gull, are also blackheaded gulls from the US, which arrive in winter markings, smudged and blurred.

Most of the winter rarities, however, (ranging from the merely uncommon to sightings a twitcher would die for,) are from the Arctic and demand a keen eye for wing-tip patterns and a feel for the whiter shades of pale. Size often helps. There was no mistaking the glaucous gull, as big as a great-black-back. I once tugged one out of a rabbit-hole (a fox had found it dead on the tideline and stashed it away).

The glaucous gull breeds right around the Arctic circle and is a regular on the west coast in winter, where it stands to be confused with the scarcer and much smaller Iceland gull. Both turn up at Galway's rubbish dump and the Galway docks or hover hopefully over the trawlers at Rossaveel. The little Ross's gull has been seen there, too.

At the beginning of January the Mayo rubbish dump near Castlebar was a scene of excited twitching when not one but two Arctic rarities were drawn to that bleak glen among the bogs. Among the hundreds of gulls wheeling above the plastic bags were, first, an ivory gull, an all-white resident of the high Arctic, very rare but notably trusting when it wanders down to Ireland.

And then, Thayer's gull, a species of such subtle definition and great rarity that its first European sighting - at Galway's rubbish dump in March, 1989 - made international ornithological news.

Thayer's gull was once thought to be a North American Arctic sub-species of the herring gull, with paler wing-tips and brown eyes, and eminently confusable, apparently, with the rare Kumlien's gull, a sub-species of the Iceland gull (also reported, on occasion, from the Galway dump). Kumlien's has so much variation in its plumage that claims to have seen one, complete with careful notes of all the shades of grey, now merely raise a groan from rare-birds committees: they really don't want to know. Thayer's gull, on the other hand, has been a separate species since 1973.

Oddly, it still does not appear in the official list of the birds of Ireland because, although pictures of the Galway gull were published in British Birds, the record was never submitted to the IWC (now BirdWatch Ireland). Natural history, too, has its Anglo-Irish tensions.

On the east coast in winter, Iceland and glaucous gulls are scarce but fairly regular visitors. More interesting ecologically are the winter habits of two much smaller gulls, the little gull and the Mediterranean gull. The first is a petite and fragile-looking bird, even smaller than the kittiwake. It dips to snatch food from the sea with all the delicacy of a tern. Little gulls breed widely in central Europe but nobody knows quite where they "belong" in winter. They seem to stay just out of sight offshore, close to the western seaboard of Europe, and to come in to the coast when pressed by strong winds.

Little gulls were once a great rarity in Ireland. Now they make annual winter appearances in Galway Bay, but the Irish Sea offers more shelter, and the birds take refuge there ahead of rising Atlantic storms. January and February are the months to look out for them, especially along the coast between Dublin and Wicklow.

The Mediterranean gull, too, has changed its habits completely. Its breeding base is in south-east Europe, with the winter months spent in the Mediterranean, and up to 20 years ago Irish records were distinctly scarce. Now, in a dramatic change, the bird has become a regular winter migrant to our eastern and southern coasts, where it merges with flocks of our own black-headed gulls (even, indeed, in Dublin's Marley Park).

Gull-watching can become an obsession, scanning great gatherings of birds for the one or two that look a bit different, or journeying to noisome rubbish tips in the hope of spotting some Arctic wanderer, the whitest, brightest bird against a wasteland of mud and black plastic. When Galway finally seals its dump later this year, the only ones to mourn may be the wistful Jonathan Livingston Seagulls, with their telescopes, field guides and thermos flasks.