Mugger of the skies who snatches catches

The most formidable of the four is the great skua, which uses brute force rather than skill to deprive gulls and terns of their catches.

It is the largest of the four species, about the size of a herring gull with a barrel chest and distinctive white flashes on the wings.

This size and strength is used on birds up to the size of a great black backed gull, and the skua will fly up to its target, suddenly grab it by the wing so it stalls in mid-air and falls into the sea.

There the skua attacks its victim until it surrenders its catch or dies.

Recent research suggests that a big increase in the numbers of great skuas

could pose a serious threat to entire populations of smaller seabirds such as puffins and kittiwakes.

The skuas have prospered because of the dumping by trawlers of fish offal and undersized fish, easy pickings for them.

But a tightening of limits for catch sizes has resulted in the skuas turning back to their traditional prey of smaller seabirds and this is taking a heavy toll.

The most commonly seen skua along the Yorkshire coast is the Arctic, which in the British Isles breeds on Shetland, Orkney, the Outer Hebrides and in the far north of the Scottish mainland.

It is the most parasitic of the skuas, stealing the catches of gulls and terns and chasing them, twisting and turning like a falcon through the sky.

The Arctic skua is a lightweight compared with the great, only 16in long excluding the long pointed tail which the adult has in summer and there are three colour phases, light, intermediate and dark.

The other two skua species, pomarine and long-tailed, are less commonly seen and both breed in the far north of Scandinavia and Russia, heading south to the warmer waters of the South Atlantic for the winter.

The pomarine skua is closely related to the great and is also a bulky and broad chested bird while the long-tailed is the smallest and most slender of the four species, only the same size as a black-headed gull and with long delicate tail streamers which give it its name.

Both feed on lemmings, other small rodents and small birds during the short breeding season on the Arctic tundra and also rob other seabirds although on passage the long-tailed skua catches much of its own food.

All four species might be encountered on the RSPB's Skua and Shearwater Cruises on the Yorkshire Belle from Bridlington.

Ring 01 262 850959 to book or e-mail bempton.cruises @rspb.org.uk for more details.

Recent local sightings have included a little stint, reported at Fairburn Ings in Leeds last Sunday.

A great northern diver was also reported at Long Nab, Burniston on Sunday and Lapland bunting was also spotted flying south at Oxenhope last Saturday.

And a brown flycatcher was reported at Brempton RSPB last Sunday.

The sighting is the second time the rare Siberian visitor has been seen in the Flamborough area, the first being in October 2007, when hundreds flocked to the village to catch a glimpse.

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CW 11/9/10