It is official and the local expert was right! The nest belongs to a Robin.
Fortunately, the Robin appears to have kept the Cowbird at bay, because there are now now 4 beautiful blue eggs in the nest. Kira saw the mother in the nest just before the bird flew at her. Mother bird than chirped frantically from a neighboring tree, obviously hoping to distract the perceived threat.
Perhaps we will have a few photos as things unfold, or hatch as the case may be. It only takes a few weeks for the birds to hatch and leave the nest.