Purple Sandpiper
Calidris maritima
Adults have short yellow legs and a medium thin dark bill with a yellow base. The body is dark on top with a slight purplish gloss and mainly white underneath. The breast is smeared with grey and the rump is black. They measure 20–22 cm (7.9–8.7 in) in length and 42–46 cm (17–18 in) across the wings, and weight is from 50–105 g (1.8–3.7 oz).
ID text from Wikipedia, CC BY-SA 4.0
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
Where you might meet both
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Play BeakBrainPhotos and recordings are credited to their authors under the licence shown. Full profiles: Purple Sandpiper and Red-necked Stint.