Black-headed Gull

The black-headed gull (Chroicocephalus ridibundus) is a small, agile gull widespread across Eurasia. Despite its English name, the breeding hood is dark chocolate-brown rather than truly black. Outside the breeding season the head becomes white with a dark ear spot behind the eye. Adults are about 38–44 cm long and average around 290 g, with pale grey upperparts, white underparts, red legs and a red bill. The white leading edge of the outer wing is conspicuous in flight.

Juveniles and first-winter birds show varying amounts of brown in the wings and back. The combination of relatively small size, quick flight, red legs and bill and the distinctive wing pattern separates adults readily from most larger gulls.

Black-headed gulls use freshwater marshes, lakes, ponds, estuaries, coastal wetlands, farmland, parks and other open landscapes. Breeding colonies are often associated with shallow wetlands or islands where the birds can nest close to water, while feeding areas may lie several kilometres away.

A GPS study of 36 breeding birds from one urban and two rural colonies in Poland found strong differences between colonies. Rural birds travelled farther and used agricultural landscapes more heavily, whereas birds from the urban colony made shorter trips and used water bodies and built-up areas more. Individual birds could also become consistent specialists on particular habitat types.

Earthworms, insects, crustaceans and other invertebrates form much of the diet, but black-headed gulls also take fish, other small aquatic prey, seeds and human-derived food. Feeding methods are equally flexible: birds pick prey from the ground, seize items from the water surface and sometimes catch insects in the air.

The same Polish GPS study found both broad generalists and individuals that repeatedly returned to the same habitat type and feeding areas. The species’ flexibility therefore occurs not only between populations but also among neighbouring birds within the same colony.

Black-headed gulls are highly social throughout much of the year, gathering in feeding flocks and forming communal resting groups outside the breeding season.

A 2018 study of resting flocks along the River Avon in Bristol found that individual gulls were most likely to match the vigilance or resting behaviour of their closest neighbour, with synchronisation weakening as social distance increased. By paying particular attention to nearby birds, a group can coordinate activity without every individual needing to monitor the entire flock.

The species is partially migratory. Birds from northern and eastern breeding populations generally move south and west after breeding, while many birds in milder western Europe remain resident. Large numbers winter around the North Sea, the British Isles, Atlantic coasts and farther south around the Mediterranean and North Africa.

Ringing studies from Scandinavia show that north-western Europe is a major wintering region, particularly Britain, the Netherlands, Belgium and France. Migration distance therefore varies greatly among populations and individuals.

Black-headed gulls are strongly colonial breeders. Colonies may contain only a few pairs or many thousands and occur at a wide range of inland and coastal wetlands, including artificial water bodies. Within colonies, each pair defends a small area around the nest while remaining surrounded by many neighbours, producing the constant mixture of calls, displays and short aggressive encounters characteristic of a gull colony.

Pairs build nests on the ground or in low vegetation, often on islands or other sites that reduce access for terrestrial predators. A typical clutch contains 2–3 eggs. Both parents incubate for about 23–26 days and care for the chicks. The young are semi-precocial, hatching covered in down and able to move around soon after hatching, but they remain dependent on their parents for food, protection and guidance. Fledging normally occurs after roughly 34–36 days.

Breeding success can vary greatly among colonies. Larger, safer colonies can benefit from many adults detecting and mobbing predators, while disturbance, flooding or repeated predation can cause near-total failure at individual sites.

The black-headed gull is classified as least concern on the IUCN Red List. It has a very large range and remains numerous globally.

This global category masks substantial regional declines, particularly in parts of northern Europe. Colony productivity can be affected by predation, disturbance, flooding and loss or deterioration of wetland breeding habitat, so local populations may require active protection even though the species is not globally threatened.