Black-headed gulls are small and one of the most abundant gulls in much of Europe and Asia, and also in eastern Canada. In summer adult birds have a chocolate-brown head (not black, although it does look black from a distance), pale grey body, black tips to the primary wing feathers, and red bill and legs. The hood is lost in winter, leaving just two dark spots. Immature birds have a mottled pattern of brown spots over most of their body.
Black-headed gulls breed in much of Europe, Asia, and in coastal eastern Canada. Most of their populations are migratory and winter further south, but some birds reside in the milder westernmost areas of Europe. Some Black-headed gulls also spend the winter in northeastern North America. They breed colonies in large reed beds or marshes, or on islands in lakes, rivers, lagoons, deltas, and estuaries. They may also occur in ponds, canals, and flood lands, nesting on the heather moors, sand-dunes or beaches. During the winter these birds are found in estuaries with sandy or muddy beaches, ploughed fields, moist grasslands, reservoirs, urban parks, farmland, and gardens.
Black-headed gulls are highly gregarious birds, both when feeding or in evening roosts; they also breed in colonies. They are rarely seen at sea far from coasts. Black-headed gulls are active during the day and feed mainly by taking prey from the surface while swimming, or by dipping the head under the surface. They also walk along the coasts and probe for aquatic prey or catch flying insects on the wing. Black-headed birds are noisy, especially in colonies, with a familiar "kree-ar" call. When feeding they utter a sharp “kek-kek”.
Black-headed gulls are monogamous breeders. This means that males will mate with only one female and females will mate with only one male. The breeding season usually starts in late March; during this time pairs become very territorial and defend their nests vigorously. Black-headed gulls nest in big colonies and built their nests on the ground in low vegetation close to each other. Females lay 1 to 3 eggs and both parents incubate them within 22-26 days. The chicks are precocial; they are hatched with eyes open and are covered in down. They are able to stand within a day, but usually stay in the nest for a week and are fed by both parents. The chicks fledge about 35 days after hatching and become reproductively mature when they are 2 years old.
Black-headed gulls don't face any significant threats at present, however, they do suffer from diseases such as avian influenza and avian botulism, from egg collection and chemical pollutants.
According to the IUCN Red List, the total Black-headed gull population size is around 4,800,000-8,900,000 individuals. National population estimates include more than 1,000 individuals on migration and more than 1,000 wintering individuals in China; 1,000-10,000 individuals on migration and more than 1,000 wintering individuals in Taiwan; more than 1,000 individuals on migration and more than 1,000 wintering individuals in Korea; less than 10,000 individuals on migration and 1,000-10,000 wintering individuals in Japan and 10,000-1 million breeding pairs and more than 1,000 individuals on migration in Russia. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.