This champion traveler, graceful in flight and delicate in form, breeds around the Arctic Ocean to the northern tip of Greenland at almost 84°N, and as far south as Cape Cod, Massachusetts. It then enjoys a “second summer” on its wintering grounds—the edges of pack ice around Antarctica. This global range extends from the northernmost land to the southernmost open water, giving this bird longer hours of daylight than any other avian species. The annual direct round-trip of perhaps 40,000 kilometers (not including daily foraging flights) may be best viewed in the context of a potential life span of 34 years or more. During these long journeys, most Arctic Terns are pelagic and rarely seen from shore, but scattered inland records from diverse parts of the world suggest that numerous individuals make long movements overland. Much remains to be learned about these great travels.
Arctic Terns forage by plunge-diving and surface-dipping for a wide variety of small fish, crustaceans, and other invertebrates, and also hawk for flying insects. In some locations, aquatic insects are the principal prey. Where nesting with Common Terns (Sterna hirundo), they take more invertebrates than that species. As in other arctic species, the breeding season is short, and Arctic Terns spend only 2 to 3 months in their nesting areas. In the large circumpolar breeding range, many nest widely dispersed in the tundra or in small colonies on islands in lakes. Others congregate at dense colonies on coastal islands. In the southern part of the breeding range in the Atlantic Ocean, Arctic Terns mingle with Common Terns. Separating these 2 very similar species is a challenge in identification. In southern Alaska, Aleutian Terns (Onychoprion aleuticus) nest with Arctic Terns in some coastal colonies.
In the nonbreeding season, the Arctic Tern is one of just 4 or 5 bird species commonly encountered in the Antarctic pack ice, but it is rarely seen by most visitors to the continent. Its biology there has received little attention but may be the key to such a notable life style. An important feature is the rapid molt of flight feathers by adult Arctic Terns during this period. In adjacent areas are several similar species, particularly the resident Antarctic Tern (S. vittata).
In breeding areas, the Arctic Tern in North America has received less attention than the Common Tern, which has very similar behavior. Comparative references are frequent in this account. Extensive studies in Europe have been summarized in three handbook accounts ( Glutz Von Blotzheim and Bauer 1982 , Cramp 1985a , Il'Icev and Zubakin 1990 ). Another handbook account summarizes information from Antarctica, as well as the Australasian region ( Higgins and Davies 1996 ). Two early studies at breeding colonies were on the Farne Islands, in northeastern England (Cullen Cullen 1956 , Cullen 1960a ), and in the eastern Gulf of Maine/outer Bay of Fundy ( Hawksley 1957 ). Both of these sites are near the southern edge of the species' range. Extensive studies north of the Arctic Circle (in the White Sea, northwestern Russia, 67°N) were also reported ( Bianki 1967 ). The notable absence of inland arctic studies is chiefly attributable to the wide dispersion of the species and thus the difficulties of assembling adequate samples, but the ferocity with which the Arctic Tern defends its nest could be a contributing factor.
The present status of the Arctic Tern is poorly known, principally because of the remote nesting areas and wide dispersion of large fractions of the population. In southern New England, after recovery from nineteenth-century slaughter for the plume trade, peripheral populations have recently declined almost to extinction, while Common Terns have prospered. In Greenland, large declines reported.
In this account, citations to named individuals refer to unpublished data supplied as personal communications; the author's unpublished data are cited as (JJH).