Look at the ringlets in the water around the Killdeer’s left foot. It is stirring the mud at the bottom of that puddle to find food — worms, insect larvae, whatever, disturbed into movement. The Killdeer is one of many bird species to use this feeding technique. Other shorebird species do it, as do herons and egrets. Avocets use their their up-curved bill to sweep along the bottom in water shallows. Depending on method, it also is known as trembling, probing, scraping, and raking.