This time I went back with my digital camera. And this time the bird left the nest, displaying the distinctive behavior that I had read about, the “broken wing act” designed to lure predators away from the nest.
Close up, they look very much like eggs and not stones, but I would have had a lot of trouble finding them if the bird hadn’t been sitting on them when I first approached.
When I left, Mrs. Killdeer had given up the broken wing act, and she and Mr. Killdeer were walking calmly back toward the nest. I think what surprised me the most was how plump she looks when she’s trying to protect the nest, either by fanning out her feathers as she did Friday, or pretending to have a broken wing as she did this time. But once she’s calmed down, she looks so much smaller. (I didn’t take a picture, but the photo at wikipedia shows how she normally looks.)