Dana, congrats on your early bluebird nest. I have seen my pair of blues the past few weeks but they have no nests started yet. But those sparrows have been trying to build nests, which I keep pulling out all their straw when I see it. I believe the pair of blues will be building a new nest within the next few weeks, but I hope they wait a while for the warmer weather.
My BB nests last year were all with white eggs (not blue) and this was a really nice change. The white eggs hatched the blue babies just like normal. Come on spring!!