But Ground Doves, like a number of birds, help maintain the quality of their feathers by throwing up sand onto their wings and backs, then shaking it off again. In doing so they create a hollowing out in the sand. I'm sure Mr Dylan thought that they were actually preparing a nest when he observed this behaviour on one of his many well attested bird-watching trips (Chronicles pp12, 15, 27-33 and chapters 8-11 passim)to the beach - or as, he called it, the windy beach far from the twisted reach of crazy sorrow.