Great Black Backed Gull (Larus marinus)
They seem to be less keen on the company of other Great Black Backs and prefer to hang around with other species of gulls and it is quite usual to see in amongst a flock of other gulls a couple of these.
They are by far the biggest of the common three and indeed of all the gulls we get in Dorset and have, as their name implies (which is not always a good guide!) a very dark back. The only possible confusion would be with the Lesser Black Backed Gull which is smaller (the size of a Herring Gull), possibly not such a dark back and in Dorset not so common.
The Great Black Backed Gull is a ferocious predator, having the advantage of size over its competitors and readily takes chicks of other gulls, terns and waders. They are also great 'muggers' watching the other species of gull around them and if they see one with food will attack and chase it until it drops the food and then swoops down to claim its prize.
Their big wing span makes them superb gliders and is wonderful to see them out at sea looking for all the world like an albatross.