Common tern

Common tern. The common tern is a medium-sized seabird in the family Laridae, widely distributed across temperate and subarctic regions of Europe, Asia, and North America. It is a graceful, long-winged bird known for its seasonal migrations between breeding and wintering grounds. The species is highly vocal and social, often nesting in dense colonies on coastal beaches, islands, and inland waterways.

Description

The common tern is a slender, pale grey and white bird with a black cap, long pointed wings, and a deeply forked tail. In breeding plumage, it sports a bright orange-red bill with a black tip and similarly colored legs, while its winter plumage shows a black bill and duller legs. It is often confused with the similar Arctic tern, but is distinguished by its longer legs, shorter tail streamers, and darker wingtips. The species exhibits slight size variation across its range, with populations in North America generally being larger than those in Europe. Its flight is buoyant and agile, characterized by rapid wingbeats as it hovers before diving for prey.

Distribution and habitat

This tern has an extensive circumpolar breeding distribution. In the Palearctic realm, it breeds from the British Isles and Scandinavia across Russia to Siberia and Japan. In the Nearctic realm, it nests from Alberta and Labrador south through the Great Lakes region and along the Atlantic coast to North Carolina. It is a long-distance migrant, with European populations wintering along the coasts of West Africa and South Africa, while North American birds travel to the Caribbean Sea, Central America, and the northern coasts of South America. Its habitat is predominantly coastal, favoring sandy or shingle beaches, barrier islands, saltmarshes, and, increasingly, human-made habitats like gravel pits and reservoir edges.

Behavior and ecology

The common tern is highly gregarious, especially during the breeding season, and is known for its aggressive defense of nesting territories against intruders like gulls and foxes. Its diet consists almost exclusively of small fish, such as sand lance and herring, which it catches by plunge-diving from the air. It also occasionally takes crustaceans and marine worms. A key aspect of its ecology is its role as an indicator species for the health of coastal and marine ecosystems. It faces predation from various mammals and birds, including the American mink and the peregrine falcon. Outside the breeding season, it forms large flocks on migration and in wintering areas.

Breeding

Breeding occurs in dense, noisy colonies, often in association with other tern species or black-headed gulls. The nest is a simple scrape in the ground, sometimes lined with shells or vegetation. The typical clutch is two to three eggs, which are incubated by both parents for about 21–22 days. Chicks are semi-precocial and leave the nest within a few days, hiding in nearby vegetation but still being fed by the adults. They fledge at approximately 22–28 days old but remain dependent on their parents for several weeks after. Breeding success is highly dependent on food availability and can be severely impacted by adverse weather, high tides, or human disturbance. The species usually first breeds at three years of age.

Conservation status

The common tern is classified as Least Concern on the IUCN Red List, with a large global population. However, many regional populations have faced significant declines due to habitat loss from coastal development, recreational pressure, and erosion. It has also been affected by pollution, including organochlorine pesticides and heavy metals, and by entanglement in fishing gear. Conservation efforts, often led by organizations like the Royal Society for the Protection of Birds and BirdLife International, include the creation of protected areas, the management of water levels at nesting sites, and the construction of artificial nesting rafts. Its legal protection under acts such as the Migratory Bird Treaty Act of 1918 in North America and the Wildlife and Countryside Act 1981 in the United Kingdom has been crucial for its recovery in some regions.

Category:Seabirds Category:Birds of Europe Category:Birds of North America