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
Sanderling
Calidris alba
The sanderling is a small plump sandpiper, 18–20 cm (7–8 in) in length. Its weight ranges from 40–100 g (1+1⁄2–3+1⁄2 oz). The winter bird is very pale, almost white apart from a dark shoulder patch. This is the source of the specific name, alba, which is the Latin for "white". Later in the summer, the face and throat become brick-red. The juvenile bird is spangled black and white, and shows much more contrast than the adult.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
And 34 more countries.
Learn this pair in BeakBrain
Photo and call practice, free in any browser.
Play BeakBrainPhotos and recordings are credited to their authors under the licence shown. Full profiles: Least Sandpiper and Sanderling.