Great Black-Backed Gull bird is the largest gull in the world, at all ages showing a heavier structure than other large gull species. Great Black-Backed Gull bird has a very bulky, deep-chested body and a deep, thick bill. The bill is yellow in the adult with a prominent red gonys spot, and the legs are stout and pink. The mantle and upperwing are black, with a white trailing edge to the wing and a bold white 'mirror' on the outer primary tips. The head and remainder of the plumage are white, with little or no head streaking in winter. Immatures take four years to mature, and in the first year are streaked on the head and underparts, with a boldly chequered pattern of black and white on the upperparts.
As its scientific name suggests, this species favours coastal habitats and nests singly or in a loose colony on rocky islands and sea cliffs, often occupying the higher ledges and clifftops. On occasion Great Black-Backed Gull bird will nest on sandy beaches and saltmarshes, or some way inland on the islands of large lakes or on moorland on drier raised ground. It is sedentary, although in winter it ranges more widely along coasts, extending seawards out over the continental shelf or penetrating a short way inland, such as along larger rivers and estuaries, onto rubbish tips and sewage outfalls, and around ports. It will scavenge, but otherwise chases and steals food from other birds.
All the calls of Great Black-Backed Gull bird are very deep and gruff, but follow similar patterns to Herring and Lesser Black-backed Gulls. The laughing 'long' display call never sounds manic or shrill and is shorter, slower and more hoarse than those species, such as "orw'orw'orw'orw'orw" or "arr'rrr'rrr'rrr'rrr'rrr". A frequently heard call is similar to the barking anxiety calls of the other species, but is much deeper and more masculine sounding, such as "ugh-ugh-ugh-ugh" or "ow'ow'ow'ow". Other calls are simple, monosyllabic, and rather strangled sounds like "aarr'ow" or "aaaow", descending at the end of the note as if calling from inside a cardboard box. Also gives an even gruffer, growling "argghhw".