Taxonomy
The terns, family Sternidae, are small to medium-sized seabirds closely related to the gulls, skimmers and skuas. They are gull-like in appearance, but typically have a lighter build, long pointed wings (which give them a fast, buoyant flight), a deeply forked tail, slender legs, and webbed feet. Most species are grey above and white below, and have a black cap which is reduced or flecked with white in the non-breeding season.
The Common Tern's closest relatives appear to be the Antarctic Tern, followed by the Eurasian Arctic and Roseate Terns. Genetic evidence suggests that the Common Tern may have diverged from an ancestral stock earlier than its relatives. No fossils are known from North America, and those claimed in Europe are of uncertain age and species.
The Common Tern was first described by Linnaeus in his Systema Naturae in 1758 under its current scientific name, Sterna hirundo. The word "stearn" was used in Old English and a similar word was used by the Frisians for tern. "Stearn" appears in the poem The Seafarer, written around 1000 AD. Linnaeus adopted this word for the genus name Sterna. The Latin for swallow is "hirundo" and refers here to the tern's superficial likeness to that unrelated bird, which has a similar light build and long forked tail. This resemblance also leads to the informal name "Sea Swallow", recorded from at least the seventeenth century. The Scottish names pictar, tarrock and their many variants are believed to be onomatopoeic, derived from the distinctive call. Due to the difficulty in distinguishing the two species, all the informal common names are shared with the Arctic Tern.
Four subspecies of the Common Tern are generally recognized, although S. h. minussensis is sometimes considered to be an intergrade between S. h. hirundo and S. h. longipennis.
| Subspecies | Breeding range | Distinctive features |
|---|---|---|
| S. h. hirundo (Linnaeus, 1758) |
Europe, North Africa, Asia east to western Siberia and Kazakhstan, and North America. | Differences between the American and Eurasian populations are minimal. American birds have a slightly shorter wing length on average, and the extent of the black tip on the upper mandible tends to be less than in birds from Scandinavia and further east in Eurasia. The proportion of black on the bill is at its minimum in the west of Europe, so British breeders are very similar to American birds in this respect. |
| S. h. minussensis (Sushkin, 1925) |
Lake Baikal east to northern Mongolia and southern Tibet. | Paler upper body and wings than S. h. longipennis, black-tipped crimson bill. |
| S. h. longipennis (Nordmann, 1835) |
Central Siberia to China, also Alaska. | Darker grey than the nominate subspecies, with shorter black bill, darker red-brown legs, and longer wings. |
| S. h. tibetana (Saunders, 1876) |
Himalayas to southern Mongolia and China. | Like the nominate subspecies, but bill is shorter with broader black tip. |
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