My sister gave me a basket that hangs on a wall. It now hangs on the wall next to my side porch. Each year I plant it with annuals. The other day I discovered that a bird had made a nest in the basket, and there was a single, robins-egg blue egg in the nest, but no robins hovered nearby. I have looked at the nest every day since, but no sign of any birds near the nest, only the solitary egg. I see plenty of robins elsewhere in the yard, but none seems to pay any attention to this nest. What could have happened to the mama robin? I hate to think of the possibilities.