Which Bird Has the Longest Migration? The Arctic Tern

How far does the Arctic tern fly?

The straight-line distance between the Arctic tern’s northern colonies and its Antarctic feeding grounds is about 19,000 km (12,000 mi) each way. For decades, books therefore gave its yearly migration as about 40,000 km (25,000 mi). Tiny light-level geolocators, which record day length and timing so scientists can work out a bird’s position, showed the true figure is far higher.

The Farne Islands bird took an especially long route. After flying south through the Atlantic, it crossed the width of the Indian Ocean and continued halfway across the South Pacific, to the area between the Ross and Amundsen Seas off Antarctica, before returning along the Antarctic coast and north through the Atlantic. That single journey was more than twice the circumference of the Earth.

Why the route is so long

Arctic terns do not fly in straight lines. On the way south, many birds from Greenland and Iceland stop for weeks in a rich feeding area in the middle of the North Atlantic, then split off Africa: some follow the African coast, others cross to South America. The return trip in spring follows a huge S-shaped curve through the Atlantic.

These detours make sense because terns ride the global wind systems, the steady trade winds and westerlies that circle the oceans. Flying with a tailwind on a longer route uses less energy than battling headwinds on a short one. The birds also feed as they travel, picking small fish and krill from the surface, so a longer route through productive water is not a cost but a way to refuel.

The reward is endless daylight. By breeding in the northern summer and spending the southern summer near Antarctica, Arctic terns see more daylight in a year than any other animal, which gives them long hours to hunt.

Lifetime distance

An Arctic tern weighs only about 100 g (3.5 oz), yet it is long-lived, and the oldest banded birds have reached about 34 years. Researchers who tracked terns from Greenland and Iceland calculated that a bird living about 30 years could fly some 2.4 million km (1.5 million mi) in its lifetime, roughly equal to three round trips from the Earth to the Moon.

Young terns make their first migration within weeks of learning to fly. One chick banded on the Farne Islands in 1982 was found in Melbourne, Australia, about three months after it fledged, more than 22,000 km (14,000 mi) away.

The bar-tailed godwit: longest nonstop flight

The longest migration and the longest nonstop flight are two different records. Arctic terns can rest on the water and feed along the way. The bar-tailed godwit, a long-legged shorebird, cannot land on the sea, so it crosses the Pacific in one go.

Godwits that breed in Alaska fly directly to New Zealand and eastern Australia each autumn, a distance of more than 11,000 km (7,000 mi). In October 2022, a five-month-old godwit fitted with a satellite tag flew at least 13,560 km (8,430 mi) from Alaska to Tasmania in about 11 days without landing, eating or drinking, a record recognized by Guinness World Records. To manage this, godwits build up huge fat reserves and shrink their digestive organs before departure.

Other long-distance champions

Several other birds make journeys that come close to, or rival, parts of the Arctic tern’s trip.

• Sooty shearwater: tracked birds from New Zealand flew about 64,000 km (40,000 mi) on their yearly migration, looping around the whole Pacific Ocean in a figure-eight.
• Northern wheatear: a songbird of about 25 g (under 1 oz) that travels some 14,000–15,000 km (about 9,000 mi) each way between Alaska and East Africa, crossing Asia.
• Common swift: migrates between Europe and Africa south of the Sahara, and outside the breeding season some swifts stay airborne for about ten months without landing.

Among other animals, humpback whales, gray whales, leatherback turtles and caribou also make very long migrations, compared in our list of the longest animal migrations.

Records and myths

Myth: the Arctic tern flies from the North Pole to the South Pole. It breeds across the Arctic and subarctic, not at the pole itself, and winters at sea along the edge of the Antarctic pack ice rather than at the South Pole.

Myth: migrating birds fly nonstop all the way. Most long-distance migrants, including Arctic terns, stop to rest and refuel. Only a few, such as the bar-tailed godwit, make ocean crossings of many days without a break.

Fact: tracking keeps raising the figures. Every time scientists fit lighter, better tags, migration distances turn out longer than expected, because birds take curving routes to use winds and food. Why birds make these journeys at all is explained in Why do birds migrate?