Lesser Black-backed Gull bird is typically a little smaller, slimmer and more graceful than the Herring Gull. The adult graellsii form in Britain has a dark slate-grey back and upperwings, rather extensive black wingtips and a small white 'mirror' on the outer primary tips; in addition, the white head of Lesser Black-backed Gull bird is blotched and streaked in winter. The Scandinavian forms intermedius and fuscus have very black upperparts, resembling Great Black-backed Gull, but all forms show yellow legs and a smaller and more slender bill. Immatures take four years to mature, and are dark brown, patterned and streaked with blackish, gradually acquiring adult plumage in stages.
Lesser Black-backed gull bird is common in American region, it typically nests colonially in similar habitat to Herring Gull, favouring grassy areas on low or rocky islands, sea cliffs, coastal dunes, also inland on moorland, bogs, lakes and increasingly on buildings in urban areas. Outside the breeding season it disperses widely, over offshore and inshore waters such as lagoons, estuaries, harbours, shorelines and tidal areas, reservoirs, gravel pits, flooded pasture, ploughed fields, farmland, urban areas and sports fields. Eastern and northern populations migrate overland to Africa, but western populations travel less far, with many wintering in Britain.
The various calls of Lesser Black-backed Gull bird are similar in pattern to both Herring and Great Black-backed Gull. The 'long-call' is deeper and more nasal than that of the Herring, such as "rru'rru'rru'rru'rru'rru..." or "egh-egh-egh-egh-egh...", and may accelerate more towards the end of the sequence. It also has a barking anxiety call, "gow'ow'ow'ow'ow", deeper and gruffer than the Herring. The simple calls are a nasal descending "eeeyhhr" or "ehrrw", or a repeated "owrr owrr owrr", all lower in pitch than Herring. It also has a more plaintive, slightly higher-pitched "i'i'i'errr" or "oo-eeerrr", given by juveniles.