Is it really vanity if he thinks it's another duck?
Poor Donald was so lonely after the death of his sole duck companion that he took to lying beside the cars where he could see a vague reflection of himself. Jeff realized Donald probably thought he was seeing another duck and was seeking company. He hangs out with three of the hens (his little harem) in the morning, but then they move on to do "chicken" activities and he's left alone. So we put a spare mirror outside near the little duck pool to watch his reaction. I think he's found a new best friend (and it's not the lurking cat)!