This gull breeds in colonies in large reedbeds or marshes, or on islands in lakes, nesting on the ground. Like most gulls, it is highly gregarious in winter, both when feeding or in evening roosts. It is not a pelagic species, and is rarely seen at sea far from coasts.
This is a bold and opportunist feeder, which will scavenge in towns or take invertebrates in ploughed fields with equal relish.
In flight, the white leading edge to the wing is a good field mark. The summer adult has a chocolate-brown head (not black, despite the name), pale grey body, black tips to the primary wing feathers, and red bill and legs. The hood is lost in winter, leaving just dark vertical streaks.
This bird takes two years to reach maturity. First year birds have a black terminal tail band, more dark areas in the wings, and, in summer, a less homogeneous hood.
This is a noisy species, especially at colonies, with a familiar "kree-ar" call.