Interesting that they knew it wasn't theirsMystery solved. A pair of house finches had a nest on the front porch. Three days ago 1 egg hatched. The parents seemed agitated, and next day the chick was gone and the nest was deserted. I blamed Scaredy Cat. Today I cleaned/removed the nest, and to my surprise found the shell of a hatched cowbird egg wrapped around a house finch egg. They knew the hatchling was an impostor and deserted the nest. If they nest again I'll be on the outlook for a 'parasitic' egg.