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Portrait of Arctic tern

Science · Biology

Arctic tern

Biology — birds, migration and navigation

The Arctic tern is a small, forked-tailed seabird weighing little more than a bar of chocolate that performs the longest migration known in the animal kingdom. It breeds in the high north through the boreal summer and then flies to the pack ice of the Southern Ocean for the austral summer, so it lives in almost perpetual daylight and sees more of the sun in a year than any other animal. Geolocators fitted to Greenland and Iceland birds in 2010 revealed an average round trip of about 70,900 km, with a previously unknown mid-Atlantic stopover; a bird from the Farne Islands was later tracked over roughly 96,000 km in a single year. Over a life that can exceed thirty years, one bird may cover the equivalent of three return journeys to the Moon.

How to spot them

  • ▸Pole to pole and back every year — the longest migration of any animal
  • ▸A black cap, blood-red bill and legs, and long tail streamers
  • ▸Experiences two summers a year and more daylight than any other creature
  • ▸Colonies mob and dive-bomb intruders, drawing blood from the scalp
  • ▸Breeds in the far north and winters on the Antarctic pack ice

Key facts

It breeds in the far north and winters on the Antarctic pack ice, the longest migration of any animal

Two summers a year, and near-continuous daylight

Miniature geolocators on Greenland and Iceland birds revealed an average round trip of about 70,900 km (2010)

Egevang and colleagues, in the Proceedings of the National Academy of Sciences; the tags weighed 1.4 g

A bird tagged on the Farne Islands was tracked over roughly 96,000 km in one year, to the Weddell Sea and back (2016)

A Newcastle University study; the longest migration ever recorded for a bird

It sees more daylight in a year than any other animal on Earth

A consequence of chasing the summer between the two polar regions

Over a lifetime of thirty years or more, it may fly the equivalent of three return trips to the Moon

Some 2.4 million km

Its forked tail and buoyant flight earned it the old English name 'sea swallow'

Shared with its relatives in the same family

Its Linnaean species name means 'of paradise', given by a Danish bishop in 1763

Erik Pontoppidan, who wrote the Natural History of Norway

Key ideas

  • The route is not a straight line: birds follow prevailing wind systems, tracing an S-shaped path down the Atlantic and using a mid-ocean stopover to fatten, so the distance flown greatly exceeds the shortest path between the poles.

Quick-fire facts

  • •Sterna paradisaea Pontoppidan, 1763; family Laridae (formerly placed in Sternidae)
  • •Weight about 85–125 g, length 33–39 cm, wingspan 76–85 cm
  • •Breeds circumpolar in the Arctic and subarctic, as far south as Northumberland, Anglesey and Massachusetts
  • •The 2010 tracking study found an average annual journey of about 70,900 km and identified a North Atlantic stopover used by birds from several colonies
  • •A Farne Islands bird tracked by Newcastle University covered roughly 96,000 km, including a non-stop crossing of the Indian Ocean
  • •Ringed birds have lived over thirty years; one Northern Irish bird reached about 34
  • •It feeds mainly by plunge-diving for small fish, especially sandeels, and its breeding success in Britain is closely tied to sandeel stocks
  • •It nests in a bare scrape on shingle or grass and defends it ferociously, striking the heads of intruders
  • •Adults have a full black cap and a uniformly red bill in summer; the similar common tern has a black-tipped red bill, and the pair are so hard to separate that birdwatchers call them 'commic terns'

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