Common Gull Bird is a medium-sized gull, superficially similar to the Herring Gull but intermediate between that and the Black-headed Gull in structure and size. It has a white head, streaked dusky in winter, with a dark eye, a gentle expression and a greenish-yellow bill. The legs are also greenish-yellow, and the wings are long with a large amount of black on the primary tips and a large white panel or 'mirror' on the very tip. The mantle and upperwings are mid-grey with a smokey-bluish tone. Immatures take three years to reach maturity, and from the first winter show mantle and head markings similar to the winter adult, with a gradually decreasing amount of dark brownish markings on the head, body, upperwing coverts and underwing. They also show more black on the primaries, and have pinkish legs and a pink base to the bill.
Common Gull Bird breeds colonially or singly, around marshes, lakes, bogs, grassy moorland, in coastal and island habitats, dunes, grassy and rocky slopes, along broad river valleys with shingle banks, and occasionally on cliffs, roofs and other elevated situations. After breeding, and in winter, Common Gull bird disperses onto grassland and farmland, often following the farmer's plough, and can be found in a wider range of wetland and dry country, such as reservoirs, gravel pits, playing fields, parks, pastures, flooded areas, and coastally in harbours, estuaries and on sandy beaches.
The calls of Common Gull bird are higher-pitched than those of the Herring Gull, which has a similar range of vocalizations, with a whining, mewing quality which gives it its other name of Mew Gull. The long call is a shrill nasal "eh' eh' eh'eh' wheeeee-yow wheeee-yow wheee-yow ee'ya ee'ya ee'ya'eh'eh", with variants such as "aah-ow aa-ow ar'ar'ar'ar'ar" and an excited "wheeyah-wheeyah-wheeyah-wheeyah'wow". These calls are uttered in flight or on the ground, when it stretches the head back and up. Various shorter calls are given, such as a rather knowing "raow!" or "arrrw!", or sharper yelps such as "arr!" and "yaow!", often breaking into sequences of shrill mewing calls.