construction styles

Outside my window at the office I've observed a turtle dove couple that have been busy building a nest. Previously this Spring, before the cold snap there were robins building a nest. I finally went out to investigate the outcome. It seems the robins abandoned the nest and the turtle doves built a nest over the top of the robin nest. It was interesting to see the different construction styles. The robins brought in string, twigs, grass and mud and put together a very strong and structurally sound nest.

The turtle doves, on the other hand, brought in a few twigs, laid them on top of the robin's nest and even though the nest doesn't seem very substantial the parents seem quite unconcerned. There must be eggs there because one of the birds is always sitting on the nest. Does the robin have more of a brain? Is the turtle dove a poor parent? I suppose that if the dove nest fails the robin nest will be there to catch the offspring.