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The arctic tern (Sterna paradisaea) is a seabird of the tern family Sternidae. This bird has a circumpolar distribution, breeding colonially in Arctic and sub-Arctic regions of Europe, Asia, and North America (as far south as Brittany and Massachusetts). The species is strongly migratory, seeing two summers each year as it migrates from its northern breeding grounds to the oceans around Antarctica and back each year. This is the longest regular migration by any known animal. Arctic terns are medium-sized birds. They are mainly grey and white plumaged, with a red beak (as long as the head, straight, with pronounced gonys) and feet, white forehead, a black nape and crown (streaked white), and white cheeks. The arctic tern is K-selected, caring for and aggressively defending a small number of young. Parents feed them fish for a considerable time, and help them fly south to winter. Arctic terns are long-lived birds, with many reaching twenty years of age. They eat mainly fish and small marine invertebrates. The species has an estimated one million individuals. Exploitation in the past has reduced this bird's numbers in the southern reaches of its range.