Arctic terns migrate from their Arctic breeding grounds to the Antarctic, traveling roughly 71,000 km (44,000 miles) round trip each year. That makes their journey the longest annual migration of any animal on Earth. They don’t simply fly in a straight line between the poles, though. Their route traces a winding path down the Atlantic Ocean, with extended stops along the way and months spent foraging among Antarctic sea ice.
From the Arctic to the Antarctic
Arctic terns breed during the northern summer across the high latitudes of the Northern Hemisphere, nesting in colonies from New England and northern Europe up through Greenland, Iceland, Scandinavia, and Arctic Canada. When summer ends, they head south. Birds depart their breeding colonies in August and don’t return until late May or early June the following year.
Their destination is the Southern Ocean surrounding Antarctica. After reaching the East Antarctic coast during the austral spring (roughly October or November), the terns gradually shift westward, following the fragmented edges of Antarctic sea ice. Research using tiny tracking devices found that the birds spend about a third of their annual cycle among this sea ice, foraging in the productive waters where ice meets open ocean. They leave the Antarctic region in the austral autumn to begin the long return flight north via the Atlantic.
The Route Is Not a Straight Line
If arctic terns flew pole to pole in a direct path, the trip would be far shorter than it actually is. Instead, tracked birds follow a sweeping S-shaped course down the Atlantic. On the southbound leg, many swing toward the coast of West Africa before curving across the mid-Atlantic toward South America, then continuing south toward Antarctica. The return trip often follows a different track up the center of the Atlantic, taking advantage of prevailing wind systems that reduce the energy cost of flight.
This zigzag strategy explains why the actual distances are so large. A tracking study that fitted 11 arctic terns with lightweight geolocators recorded an average annual distance of 70,900 km, with individual birds ranging from 59,500 to 81,600 km. Some individuals exceeded 80,000 km in a single year, the longest round-trip animal migration ever recorded electronically.
How They Feed Along the Way
Arctic terns are not simply endurance flyers pushing through without stopping. They are plunge divers that feed on small fish and invertebrates near the ocean surface, flying low over the water to spot prey. During migration, however, they’ve been recorded at altitudes above 1,000 meters, and they’ve even been observed crossing the Andes mountains. This suggests they alternate between high-altitude transit flying and lower foraging flights when they encounter productive waters.
The stopover zones where terns pause to refuel tend to be areas of high ocean productivity: upwelling regions off the coasts of Africa and South America, and the nutrient-rich waters near the Antarctic ice edge. These aren’t random rest stops. The birds appear to time their movements to exploit seasonal bursts of marine life along the route.
Why Antarctica?
The logic behind this extreme migration is simple: daylight and food. By moving between the Arctic and Antarctic summers, arctic terns experience more daylight hours per year than any other animal. The long polar days give them extended foraging time at both ends of the journey. Antarctica’s summer waters are extraordinarily productive, teeming with krill and small fish near the sea ice edge. For a bird that hunts by sight in shallow dives, those endless daylight hours over rich feeding grounds are worth the enormous travel cost.
How They Navigate
Crossing tens of thousands of kilometers of open ocean requires remarkable navigational ability. Scientists still don’t fully understand how migratory birds pull this off, but research points to several overlapping systems. Birds appear to sense Earth’s magnetic field, using differences in magnetic intensity and inclination as a kind of built-in map. Experiments with other migratory species show that disrupting magnetic particles in adult birds changes their orientation, while juveniles (who haven’t yet developed a full internal map) are unaffected.
Magnetic sensing likely works alongside other cues. Birds may use the position of the sun and stars, and possibly even smell, to cross-reference their location. No single system fully explains the precision of long-distance migration. The current best guess is that experienced adults combine magnetic information with learned landmarks and celestial patterns to stay on course across featureless ocean.
A Lifetime of Miles
Arctic terns live 20 to 30 years on average, with the oldest recorded individual reaching 34. When you multiply those decades by 70,000+ km per year, the numbers become staggering. Over a typical lifetime, a single arctic tern may fly roughly 2.4 million km (1.5 million miles). That’s the equivalent of circling Earth about 60 times, or making more than three round trips to the moon.
This lifetime total makes the arctic tern not just the champion of annual migration but the most-traveled animal in the history of the planet, covering more distance in its small body than many species could manage in theory. Every year, from August to June, they trace the same enormous loop between the poles, chasing an endless summer from one end of the Earth to the other.