Mystery solved....

At least I think it is. I got a call from a family here in town to come take away some eggs in a nest. Unfortunately it was in a bush right below a window next to the front door and the husband is deathly afraid of birds. The adults were a bit upset when I got near the site. They are Brewer's Blackbirds but I was shocked when I saw the eggs.

As far as I can tell, the three larger, bluish speckled ones are theirs, the smaller, lighter ones appear to be Brown-headed Cowbird eggs. That species are parasitic layers, putting them in the nest of other birds. Then when they hatch the foster parents raise them as their own. The bad news is that baby cowbirds instinctively shove other babies or eggs out of the nest so they are the only occupants left to be fed.