Black-headed bird is the familiar small gull in American region, the adult in summer has a chocolate-brown (not black!) head, with a short transitional state between this and the winter plumage of just a dark smudge over the eye and a bold dark ear-spot on a white head. The upperparts of Black-headed bird are pearly-grey, with a long white wedge from the primary coverts to the outer primary tips, a black trailing edge to the primaries and smoky-grey underside to the flight feathers. Immature birds take two years to mature, are blotched and marked with dark brown, in decreasing amounts with age, but adults always have a roughly similar pattern of black and white on the primaries.
Black-headed Bird is common throughout American region and fairly ubiquitous in most wetland habitats. In the breeding season, Black-headed Bird nests around both shallow brackish and saline marshy pools, lakes, gravel pits, reedbeds, saltmarshes, estuaries, broad slow-moving rivers and flooded areas, often favouring small shingly islands for security, but also on drier areas close to water, such as heather moors and dunes. Outside the breeding season it is found even more widely, in urban areas, parks, playing fields, sewage farms, rubbish tips, reservoirs, inlets, estuaries and intertidal areas.
Black-headed bird is very vocal, particularly around breeding colonies, where the noise can be deafening and often continues through the night. It has a variety of rather unattractive harsh calls, the common call being a slurred screech, "krreearr" or "kaa'aarrr". It gives a harsher and insistent "raaargh!" or "gaaarhh!" when reacting anxiously to the presence of intruders, but also has a softer and less urgent "aaarrrr", an "akh'akh'akh" and singles and multiples of "kik", delivered in a more conversational tone. A longer and more elaborate call, "kre-kre-kreh'kraaa'kraaaa'kraaaa'kraaaa", is given in various social contexts.