page_title: Arctic tern
section_title: Reproduction
hierarchical_section_title: Arctic tern / Reproduction
caption_attribution_description: English: Arctic tern nesting on Iceland, Jökulsárlón
context_page_description: The Arctic tern is a tern in the family Laridae. This bird has a circumpolar breeding distribution covering the Arctic and sub-Arctic regions of Europe, Asia, and North America. The species is strongly migratory, seeing two summers each year as it migrates along a convoluted route from its northern breeding grounds to the Antarctic coast for the southern summer and back again about six months later. Recent studies have shown average annual roundtrip lengths of about 70,900 km for birds nesting in Iceland and Greenland and about 90,000 km for birds nesting in the Netherlands. These are by far the longest migrations known in the animal kingdom. The Arctic tern flies as well as glides through the air. It nests once every one to three years; once it has finished nesting it takes to the sky for another long southern migration.
  Arctic terns are medium-sized birds. They have a length of 28–39 cm and a wingspan of 65–75 cm. They are mainly grey and white plumaged, with a red/orangish beak and feet, white forehead, a black nape and crown, and white cheeks. The grey mantle is 305 mm, and the scapulae are fringed brown, some tipped white.
context_section_description: Breeding begins around the third or fourth year. Arctic terns mate for life and, in most cases, return to the same colony each year. Courtship is elaborate, especially in birds nesting for the first time. Courtship begins with a so-called "high flight", where a female will chase the male to a high altitude and then slowly descend. This display is followed by "fish flights", where the male will offer fish to the female. Courtship on the ground involves strutting with a raised tail and lowered wings. After this, both birds will usually fly and circle each other.
  Both sexes agree on a site for a nest, and both will defend the site. During this time, the male continues to feed the female. Mating occurs shortly after this. Breeding takes place in colonies on coasts, islands and occasionally inland on tundra near water. It often forms mixed flocks with the common tern. It lays from one to three eggs per clutch, most often two.
  It is one of the most aggressive terns, fiercely defensive of its nest and young. It will attack humans and large predators, usually striking the top or back of the head. Although it is too small to cause serious injury to an animal of a human's size, it is still capable of drawing blood, and is capable of repelling many raptorial birds, polar bears  and smaller mammalian predators such as foxes and cats. Other nesting birds, such as alcids, often incidentally benefit from the protection provided by nesting in an area defended by Arctic terns.
  The nest is usually a depression in the ground, which may or may not be lined with bits of grass or similar materials. The eggs are mottled and camouflaged. Both sexes share incubation duties. The young hatch after 22–27 days and fledge after 21–24 days. If the parents are disturbed and flush from the nest frequently the incubation period could be extended to as long as 34 days.
  When hatched, the chicks are downy. Neither altricial nor precocial, the chicks begin to move around and explore their surroundings within one to three days after hatching. Usually they do not stray far from the nest. Chicks are brooded by the adults for the first ten days after hatching. Both parents care for hatchlings. Chick diets always include fish, and parents selectively bring larger prey items to chicks than they eat themselves. Males bring more food than females. Feeding by the parents lasts for roughly a month before being weaned off slowly. After fledging, the juveniles learn to feed themselves, including the difficult method of plunge-diving. They will fly south to winter with the help of their parents.
  Arctic terns are long-lived birds that spend considerable time raising only a few young, and are thus said to be K-selected. The bird has life span that was thought be around 20 years, however National Geographic, The University of Alberta & Massachusetts Institute of Technology, concluded in 2010 that more than 50% of this species will live past their 30th birthday. A study in the Farne Islands estimated an annual survival rate of 82%.
caption: Arctic tern nesting in southern Iceland
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