Arctic Tern (Sterna paradisaea): Facts and Record Migration

What does an Arctic tern look like?

The Arctic tern is a slender, graceful bird built for flight. In the breeding season it has a neat black cap that covers the forehead and nape, white cheeks, pale gray upperparts and soft gray underparts that make the white cheek stripe stand out. The bill, short legs and webbed feet are a deep blood red.

The wings are long, narrow and pointed, and the tail is deeply forked with long white streamers that extend to or just beyond the wingtips when the bird is perched. Seen from below in flight, the flight feathers look almost translucent, with a thin, sharp black line along the trailing edge of the outer wing. Males and females look alike.

After breeding, the forehead turns white and the bill and legs darken to black. Young birds have a dark bill, a white forehead and a scaly gray-brown pattern on the back. Arctic terns are easy to confuse with common terns, which share many colonies; the Arctic tern has a shorter, all-red bill, very short legs that make it look crouched, and a more rounded head.

How big is an Arctic tern?

Despite its long journeys, the Arctic tern is a lightweight bird, weighing about as much as a small apple. Much of its length is tail.

The long, narrow wings give the bird a high aspect ratio, the same principle used for gliders. This shape lets it fly for hours with little effort, glide on ocean winds and hover in place over the water before diving.

Habitat and range

The Arctic tern breeds right around the top of the world. Colonies are found on coasts, offshore islands and tundra near water in Iceland, Greenland, Scandinavia, Svalbard, Arctic Russia, Alaska and northern Canada. The breeding range reaches south to Britain and Ireland, the Netherlands, Germany, Brittany in France and, in North America, to Maine and Massachusetts.

More than half of the world population nests in Europe, and Iceland is one of the most important countries for the species. In Britain the largest colonies are in Orkney and Shetland, and the Farne Islands off Northumberland are a famous place to see them at close range.

From August onward, the terns leave the north and head south over the Atlantic and Pacific Oceans. They spend the southern summer at sea in the Southern Ocean, feeding along the edge of the Antarctic pack ice, before flying north again in spring. Outside the breeding season they stay far offshore, so they are rarely seen from land on migration.

The longest migration on Earth

For a long time, the Arctic tern’s yearly journey was estimated at about 40,000 km (25,000 mi), based on the straight-line distance between its summer and winter homes. Modern tracking with tiny geolocators showed the real distance is much longer, because the birds follow winding routes that make use of prevailing winds and rich feeding areas.

A 2010 study of terns breeding in Greenland and Iceland measured an average round trip of about 70,900 km (44,100 mi), and up to 81,600 km (50,700 mi). Terns from the Netherlands, which follow the coasts of Europe and Africa, traveled about 48,700 km (30,300 mi). One bird tagged on the Farne Islands covered about 96,000 km (60,000 mi) in ten months, crossing the Atlantic and Indian Oceans and reaching the Pacific side of Antarctica.

Researchers estimated that a tern living about 30 years could fly some 2.4 million km (1.5 million mi) in its life, the same as about three round trips to the Moon. How this compares with the bar-tailed godwit’s nonstop record and other long-haul flyers is explained in Which bird has the longest migration?, and how young terns find their way is covered in How do birds know where to migrate?

What do Arctic terns eat?

Arctic terns are carnivores that feed mostly on small fish, usually less than about 10 cm (4 in) long. Typical prey includes sand eels (sand lances), capelin, young herring and cod, and other small schooling fish. They also take krill, amphipods, small crabs and other crustaceans, especially in the Southern Ocean, and on the breeding grounds they catch insects, sometimes in the air.

The tern hunts by flying slowly over the water, often hovering on fast-beating wings, then plunging steeply to snatch prey from just below the surface. Unlike gannets or pelicans it does not dive deep, and it often only dips its bill or head into the water. It may also pick food from the surface in flight or steal fish from other terns, puffins and grebes.

Food supply strongly controls breeding success. When sand eel stocks collapsed around Shetland and Iceland, many colonies failed to raise chicks for several seasons in a row.

Behavior and colony life

Arctic terns are social birds that nest in colonies, from a few pairs to several thousand, often alongside common terns, eiders and puffins. Colonies are noisy places full of harsh, rasping “kee-arr” calls and short alarm notes.

They are famous for defending their nests. When a fox, gull, dog or person enters a colony, the terns rise into the air, scream and dive-bomb the intruder, often striking the top of the head with their sharp bills. They are too small to cause serious injury, but they can draw blood, and their attacks can drive off predators much bigger than themselves. Eider ducks and other birds often nest inside tern colonies for this protection.

Courtship includes a “fish flight”, in which the male parades with a fish in his bill and offers it to the female, and high display flights in which the pair climbs steeply before gliding down together. Most birds keep the same partner for years and return to the same colony each summer.

Reproduction and life cycle

Arctic terns usually start breeding at three or four years old. The nest is a simple scrape in sand, gravel, shingle or moss, sometimes lined with a little grass or shell. The female lays one to three mottled, well-camouflaged eggs, most often two, from late May to early July depending on latitude.

Both parents share incubation, which lasts about 22–27 days. The chicks hatch covered in down and are able to walk within a day or two, but they stay near the nest and hide in vegetation while the adults bring fish. They fly at about 21–24 days old and are fed by their parents for some weeks more, while they learn the tricky skill of plunge-diving.

Young terns migrate south with the adults in their first autumn. Most then stay in the Southern Hemisphere or at sea for their second year before returning north to the colonies.

How long do Arctic terns live?

For a bird of about 100 g, the Arctic tern is remarkably long-lived. Many adults reach 15–30 years, and the North American banding record is about 34 years. Adult survival from one year to the next is high, which makes up for the small number of chicks each pair raises.

Chicks and eggs face the greatest risks. Gulls, skuas, foxes, rats, mink, stoats, cats and hedgehogs on some islands all take eggs or young, and bad weather or food shortages can wipe out a season’s breeding in a colony.

Conservation status

The IUCN Red List classifies the Arctic tern as Least Concern because it has an enormous range and a large population, estimated at more than two million birds. However, the global population trend is thought to be decreasing, and several regional populations have fallen sharply.

In the late nineteenth century, terns in New England were shot in huge numbers for the hat-feather trade, and protection laws such as the Migratory Bird Treaty Act of 1918 helped them recover. Today the main threats are food shortages linked to warming seas and fishing, predators introduced to islands, disturbance of colonies, and changing sea ice in the Antarctic. In Iceland the species was regionally classed as Vulnerable in 2018 after sand eel stocks crashed.

Conservation work includes removing rats and mink from nesting islands, restoring colonies in Maine with decoys and wardens, and protecting colonies from disturbance during the breeding season.

Myths and facts

Myth: Arctic terns fly straight from the Arctic to Antarctica. Tracking shows they take long, curving S-shaped routes across the oceans, following winds and stopping to feed in rich areas, which is why the real distance is far greater than a straight line.

Myth: Arctic terns live only in the Arctic. They breed as far south as Brittany and Massachusetts and spend about half the year near Antarctica.

Fact: Arctic terns see two summers a year. By leaving the north in late summer and arriving in the south for the austral summer, they spend most of the year in long daylight.

Arctic terns and people

The Arctic tern has inspired people for centuries with its endurance. It appears on postage stamps from Canada, Iceland, Finland, the Faroe Islands and other places, and a European constellation of polar-orbiting weather satellites, EPS-Sterna, is named after it.

Colonies on the Farne Islands, in Shetland, Iceland and Maine are popular with birdwatchers, and the same islands are often home to puffins (see our Atlantic puffin profile). Visitors should keep to marked paths, wear a hat and move away if the terns start alarm-calling. For other record travelers, including whales and caribou, see our list of the longest animal migrations.