Red-necked Stint
Calidris ruficollis
These birds are among the smallest of waders, very similar to the little stint, Calidris minuta, with which they were once considered conspecific. The red-necked stint's small size, fine dark bill, dark legs and quicker movements distinguish this species from all waders except the other dark-legged stints. It measures 13–17 cm (5.1–6.7 in) in length, 28–37 cm (11–15 in) in wingspan, and 21–51 g (0.74–1.80 oz) in weight.
ID text from Wikipedia, CC BY-SA 4.0
Upland Sandpiper
Bartramia longicauda
An adult is roughly 30 cm (12 in) long with a 66 cm (26 in) wingspan. The average weight is 170 g (6 oz). This odd bird has a small dove-like head on a long neck. It is heavily marbled black and brown on the back and wings. The neck is streaked with dark brown which continues down to the breast and on to the flanks. The belly and undertail coverts are white, and the tail is quite long for a sandpiper. The upland sandpiper also has a white eye-ring and long yellow legs. Voice: Upland sandpipers can be identified by a distinctive call, sometimes called a "wolf whistle", which features a long, ascending whistle followed by a second rising and/or falling call. These sounds are often made while the bird is landing or while flying high.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play BeakBrainPhotos and recordings are credited to their authors under the licence shown. Full profiles: Red-necked Stint and Upland Sandpiper.