River Tern vs South American Tern

River Tern

Sterna aurantia

Medium166 gRiverine

It is a medium-large tern, 38–46 cm long with an 80–85 cm wingspan, distinctly larger than any other species in Sterna and more comparable in size to a Sandwich tern (Thalasseus sandvicensis) or a lesser crested tern (T. bengalensis). It has dark grey upperparts, white or very pale grey underparts, a forked tail with long flexible streamers, and long pointed wings with pale grey primaries. The bill is stout for a tern, bright yellow in summer and duller yellow with a dusky tip in winter, and the legs bright red.

ID text from Wikipedia, CC BY-SA 4.0

Photo: Parth Kansara · CC BY 4.0

South American Tern

Sterna hirundinacea

Medium188 gMarine

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

Photo: Chris Pearson from Leuchars, Scotland · CC BY 2.0

Photos and recordings are credited to their authors under the licence shown. Full profiles: River Tern and South American Tern.