I saw this bird (the one on the left) in the tree with papa bluebird this afternoon.
They eyed each other somewhat warily. I thought at first it was the phoebe who has built a nest by my door, but this bird's color is much darker than the phoebe, and the breast is more starkly white. The phoebe is more brownish and buff in comparison. I thought it might be the male but my book doesn't seem to discern between the phoebe genders in that way.
I like it - it's a fairly distinctive bird now that I know what it is, especially by those white tail feather tips. I will know it when I see it again now. I like that "feature" about a bird - being able to recognize it again!