One of the sandpipers is quite different. Look at the bird in the foreground in the first photo. The back is more cleanly spotted than on any of the yellowlegs. A clear white ring surrounds the eye. Last, but not least, the legs are greenish rather than yellow--all field marks of a Solitary Sandpiper.
The eye ring is not fool-proof. In the last photo you can see that Lesser Yellowlegs also show white eye rings. The legs, however, are yellow and the back not cleanly spotted. This last photo was taken at the Minnesota Valley National Wildlife Refuge.
Sandpiper bills are used to illustrate ecological partitioning. Species with relatively long bills can specialize in prey deeply buried in the mud, while those with shorter bills go after invertebrates at respectively shallower depths. (Obviously those with longer legs can also forage in deeper water.)