The great black-backed gull (Larus marinus) is quite common along the Dorset coast although by no means as numerous as the black-headed or herring gulls but you can potentially see them anywhere along the coastline from the harbours to the cliffs.
They do not seem to be 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 a couple in amongst a flock of other gulls.
They are by far the biggest of the common three and, indeed, of all the gulls we get in Dorset. They 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) and possibly not such a dark back. It is far less common in Dorset than the greater.
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.