Editing Common tern (section)

===Similar species===


There are several terns of a similar size and general appearance to the common tern. A traditionally difficult species to separate is the Arctic tern, and until the key characteristics were clarified, distant or flying birds of the two species were often jointly recorded as "commic terns". Although similar in size, the two terns differ in structure and flight. The common tern has a larger head, thicker neck, longer legs, and more triangular and stiffer wings than its relative, and has a more powerful, direct flight.<ref name= BB86/> Arctic terns have greyer underparts than the common variety, which makes its white cheeks more obvious, whereas the rump of the common tern can be greyish in non-breeding plumage, compared to the white of its relative. The common tern develops a dark wedge on the wings as the breeding season progresses, but the wings of the Arctic stay white throughout the northern summer. All the [[flight feather]]s of the Arctic tern are translucent against a bright sky, only the four innermost wing feathers of the common tern share this property.<ref name=BB86/><ref name=vanDuivendijk/> The trailing edge of the outer flight feathers is a thin black line in the Arctic tern, but thicker and less defined in the common.<ref name=vinicombe/> The bill of an adult common tern is orange-red with a black tip, except in black-billed ''S.{{nbs}}h.{{nbs}}longipennis'', and its legs are bright red, while both features are a darker red colour in the Arctic tern, which also lacks the black bill tip.<ref name=BB86>{{cite journal |last=Hume |first=Rob A |year=1993 |title=Common, Arctic and Roseate Terns: an identification review |journal=British Birds |volume=86 |pages=210–217}}</ref>

In the breeding areas, the roseate tern can be distinguished by its pale plumage, long, mainly black bill and very long tail feathers.<ref name=vanDuivendijk>van Duivendijk (2011) pp. 200–202.</ref> The non-breeding plumage of roseate is pale above and white, sometimes pink-tinged, below. It retains the long tail streamers, and has a black bill.<ref name=olsen2>Olsen & Larsson (1995) pp. 69–76.</ref> In flight, the roseate's heavier head and neck, long bill and faster, stiffer wingbeats are also characteristic.<ref name=Blomdahl>Blomdahl et al. (2007) p. 340.</ref> It feeds further out to sea than the common tern.<ref name=olsen2/> In North America, the [[Forster's tern]] in breeding plumage is obviously larger than the common, with relatively short wings, a heavy head and thick bill, and long, strong legs; in all non-breeding plumages, its white head and dark eye patch make the American species unmistakable.<ref name=olsen3>Olsen & Larrson (1995) pp. 103–110.</ref>

In the wintering regions, there are also confusion species, including the Antarctic tern of the southern oceans, the [[South American tern]], the [[Australasia]]n [[white-fronted tern]] and the [[white-cheeked tern]] of the [[Indian Ocean]]. The plumage differences due to "opposite" breeding seasons may aid in identification. The Antarctic tern is more sturdy than the common, with a heavier bill. In breeding condition, its dusky underparts and full black cap outline a white cheek stripe. In non-breeding plumages, it lacks, or has only an indistinct, carpal bar, and young birds show dark bars on the [[Flight feather#Tertials|tertials]], obvious on the closed wing and in flight.<ref name=Enticott196>Enticott & Tipling (2002) p. 196.</ref><ref name=SASOL>Sinclair et al. (2002) p. 212.</ref> The South American tern is larger than the common, with a larger, more curved red bill, and has a smoother, more extensive black cap in non-breeding plumage.<ref name=peru>Schulenberg et al. (2010) p. 154.</ref> Like Antarctic, it lacks a strong carpal bar in non-breeding plumages, and it also shares the distinctive barring of the tertials in young birds.<ref name=Enticott192>Enticott & Tipling (2002) p. 192.</ref> The white-fronted tern has a white forehead in breeding plumage, a heavier bill, and in non-breeding plumage is paler below than the common, with white underwings.<ref name=Simpson/> The white-cheeked tern is smaller, has uniform grey upperparts, and in breeding plumage is darker above with whiter cheeks.<ref name=grimmett>Grimmett et al. (1999) pp. 140–141.</ref>

Juvenile common terns are easily separated from similar-aged birds of related species. They show extensive ginger colouration to the back, and have a pale base to the bill. Young Arctic terns have a grey back and black bill, and juvenile roseate terns have a distinctive scalloped "saddle".<ref name=vinicombe>Vinicombe et al. (1990) pp. 133–138.</ref> [[Hybrid (biology)|Hybrids]] between common and roseate terns have been recorded, particularly from the US, and the intermediate plumage and calls shown by these birds is a potential identification pitfall. Such birds may have more extensive black on the bill, but confirmation of mixed breeding may depend on the exact details of individual flight feathers.<ref name=olsen/>