Dunlin
Calidris alpina
Measurements: Length: 16–20 cm (6.3–7.9 in) Weight: 34–77 g (1+1⁄4–2+3⁄4 oz) Wingspan: 38–43 cm (15–17 in) An adult dunlin in breeding plumage shows the distinctive black belly which no other similar-sized wader possesses. In winter, dunlins are greyish-brown above and white below. Juveniles are brown above with two weak whitish "V" shapes on the back, though less obvious than the same feature on little stint and some other species in the genus. They usually have black marks on the flanks or belly. All ages show a narrow white wingbar in flight. The legs and slightly decurved bill are black.
ID text from Wikipedia, CC BY-SA 4.0
Least Sandpiper
Calidris minutilla
This species has yellow-green legs and a short, thin, dark bill. Breeding adults are brown with dark brown streaks on top and white underneath. They have a light line above the eye and a dark crown. In winter, Least sandpipers are grey above. The juveniles are brightly patterned above with rufous colour and white mantle stripes. This bird can be difficult to distinguish from other similar tiny shorebirds; these are known collectively as "peeps" or "stints". In particular, least sandpiper is very similar to its Asian counterpart, long-toed stint.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
And 2 more countries.
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