I can't give you a definitive answer woodsidetrader, but in my experience, robins aren't aggressive like that. I've seen them build on an old nest (with no other birds using it this season). In fact, I've seen them build pretty tall nests on top of old nests, but I really don't think they are aggressive to over-take an already occupied nest. I think maybe something else may have disturbed the dove's nest and the robin found an empty nest to build on top of. I could be wrong........but that's my thought.