How long can an Arctic tern’s annual migration reach, in kilometres?

An Arctic tern’s annual migration can reach about 90,000 kilometres.

Arctic terns migrate between Arctic breeding grounds and Antarctic waters, following a route that lets them experience summer in both polar regions. The full journey can include detours and zigzagging rather than a straight line, which helps explain why modern tracking estimates are much longer than older simple distance calculations.

The species is a small seabird with a grey body, white underside, black cap, and deeply forked tail. It feeds on fish and marine invertebrates, often catching prey near the surface. Arctic terns usually return to the same broad breeding regions after their southern migration.

The exact distance varies among individuals and populations. Earlier estimates were often around 40,000 kilometres per year, while geolocator studies found some birds travelling roughly 70,000 to 90,000 kilometres. This makes the Arctic tern one of the greatest long-distance migrants known.