Across the lonely beach we flit,
One little sandpiper and I,
And fast I gather, bit by bit,
The scattered drift-wood, bleached and dry.
The wild waves reach their hands for it,
The wild wind raves, the tide runs high,
And up and down the beach we flit,
One little sandpiper and I.
From The Sandpiper, by Celia Thaxter, 1883
Thaxter's writing about the poem makes it clear that its source was an encounter with a plover near its nest, but her description makes it sound as if she was watching a Sanderling (Calidris alba), the most common sandpiper on open ocean beaches almost anywhere in the world. Had it been a Sanderling, she would have marveled at its hyperactivity as it charged the ocean waves and then retreated as the waves charged back.
Sanderlings are particularly common on the Pacific Northwest coast, where the richness of the ocean waters enhances the productivity of the intertidal zone. The only higher densities recorded for the species in the Americas in winter are along the Humboldt Current beaches of Peru and Chile. Flocks of hundreds of birds occur all along our outer beaches, and they are tame enough (and presumably used to crowds of people) that you can watch their foraging behavior at great length.
Sanderlings dash in and out of the waves to get prey exposed by the receding water, but they also spend much time above the waves running around on either dry or wet sand. Like many other sandpipers, they can find their prey either visually or tactilely.
Tactile foraging involves plunging their slightly opened bill into the sand at frequent intervals as they run, like an animated sewing machine, to search for prey. When a prey item is felt, the bill tip closes on it and extracts it from the sand. Sanderlings foraging like this leave characteristic series of probe holes.
When foraging visually, a Sanderling moves just as rapidly and must have superb vision to see the tiny prey items that it seeks. Many amphipod crustaceans are taken this way, but some days they seem to be hunting thin worms, polychaetes of the family Capitellidae. This prey item is not mentioned in the most recent account of Sanderling natural history, yet all birds appeared to be feeding on them on a recent February visit to Long Beach, Washington.
A bird would move rapidly along, then suddenly stop and grab an incredibly thin worm and pull it quickly from the substrate. It would swallow it in a few gulps, sometimes running off while doing so. Birds were crisscrossing in front of us constantly, presumably spaced out to avoid direct competition for a single prey item. Hundreds of worms were being consumed, but I am sure there were many more where those came from.