Soon they would run up the beach towards this one discrete, darkened patch in the sand:
And then they would start to probe very actively. Below, note the difference in sand texture at the top and bottom of the picture. (The smooth sand at the top of the picture is outside of the probed area.)
After a few minutes, the Sanderlings would run back down the beach to the water's edge. But they couldn't seem to stay away from this patch. It was like a magnet to them! They would return to the patch over and over again. There must have been a high density of prey at that site!
As the Sanderlings made their way to the water, their bills were noticeably coated in sand:
Just looking at this picture makes me want to shake my head (to get the sand off). And that made me wonder about why the Sanderlings were returning to the water every now and then. Were they washing the sand off their bills in between feeding bouts?