Most Sandpiper species are pretty similar, specially as they come to Costa Rica in non-breeding plumage. Having a few different species mixed up in a single group can help for identification, as some of them will be showing the breeding plumage that distinguishes them, as well as other features like leg color. In this case, the Least Sandpiper has yellow legs, distinguishing it from the very similar Semipalmated Sandpiper. Also this bird is similar to the Pectoral Sandpiper, however the Pectoral is a lot bigger, has a yellowish bill, and the breast is streaked and delineated vs the white belly.

A partial reflection of the Sandpiper as it probes the water for food

This one was searching for food from the comfort of the rocks

Ripples on the water surface are formed as this Sandpiper wades through the shallows

This Sandpiper waded through the shallow waters in non-bredding plumage, which is a lot less colorful

Another Least Sandpiper in non-breeding plumage, this time foraging at the pond’s edge