Whiskered Tern
Chlidonias hybrida
The size, black cap, strong bill (29–34 mm in males, 25–27 mm and stubbier in females, with a pronounced gonys) and more positive flight recall common or Arctic tern, but the short, forked-looking tail and dark grey breeding plumage above and below are typically marsh tern characteristics. The summer adult has white cheeks and red legs and bill. The crown is flecked with white in the juvenile, and the hindcrown is more uniformly blackish, though in the winter adult this too is flecked with white.
ID text from Wikipedia, CC BY-SA 4.0
White-winged Tern
Chlidonias leucopterus
Adult birds in summer have short red legs and a short black bill (small and stubby, measuring 22–25 mm from the feathers, decidedly shorter than the head), a black neck (often with a pale gray back) and belly, very dark grey back, with a white rump and light grey (almost white) tail, which often looks 'square' in juveniles. The face is tinged yellowish. The wings, as the name implies, are mainly white. The inner wing is grayish with brown-tipped coverts.
ID text from Wikipedia, CC BY-SA 4.0
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