Roseate Tern
Sterna dougallii
This is a small-medium tern, 33–36 cm (13–14 in) long with a 67–76 cm (26–30 in) wingspan, which can be confused with the common tern, Arctic tern, and the larger, but similarly plumaged, Sandwich tern. The thin sharp bill is black, with a red base which develops through the breeding season, and is more extensive (to fully red) in the tropical and southern hemisphere subspecies. It is shorter-winged and has faster wing beats than common or Arctic tern. Voice: The call of the roseate tern is a very characteristic chuwit, similar to that of the spotted redshank, quite distinct from other terns.
ID text from Wikipedia, CC BY-SA 4.0
South American Tern
Sterna hirundinacea
With adult South American terns reaching a length of 40 to 44 centimetres (16 to 17 in), they are larger than either common terns (Sterna hirundo) or Arctic terns (Sterna paradisaea). Otherwise they closely resemble these species in plumage at all times of year. The beak is larger and is red in adults, and they do not have a dark-coloured bar on the carpus of the wing. The black cap extends below the eye, usually separated from it by a white crescent, and the rear edge of the cap is neatly defined.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Roseate Tern and South American Tern.