In this photo we have 3 larger birds which are American Avocets, and 4 smaller shorebirds mainly in feeding postures with their bills deep in water to their bellies, and one with a long straight bill. Being considerably smaller, chunky looking, and having a long straight bill, makes it easy to call these dowitchers.
Closer study shows some interesting observations. Two of the birds - front left and back right - are noticeably larger than the other two, suggesting Long-billed's. The bellies of the larger birds are higher out of the water, meaning their legs are taller. The structure of their bodies is bulkier and rounder (hump backed) than the other two; Kevin Karlson describes this as shaped like a tennis ball. These are, indeed, Long-billed Dowitchers. Compare to the Short-billed's, whose bodies are more stretched-out, oval shaped, and leaner. These two points are often clear enough to separate and identify Long-billed Dowitchers from a distance, in silhouette.
For further information about dowitchers and shorebirds, I highly recommend the excellent book, The Shorebird Guide by Michael O'Brien, Richard Crossley and Kevin Karlson.
photo © adrian binns