I'm not a shorebird expert, but the size, shape and colouring of Semipalmateds is virtually identical to that of Leasts. They key field marks, which this bird appears to have, are dark legs and a stouter bill which is not down-curved. You can also separate them by their call, but that's a bit tough in a photo. :wink:
White-rumped are slightly larger: noticeable if they're with Least & semi-palms, but not so obvious if they're by themselves. The best field mark for them (if they don't spread their wings and show you their white rump) is the black spots on the flanks: subtle but distinctive.
BB
