A brown speckled cowbird egg in a blue bird nest.  An interloper!  Early in the morning when the bluebirds fly around looking for bugs, the cowbird comes to the nest and lays its egg.  Then it removes the blue egg.  It must think the parents are color blind!  It leaves the same number hoping the bluebird won’t notice the difference (so said a wild bird expert).  Two broken blue eggs lay on the ground below this nesting box.  I interfered with nature and removed the brown egg.  Days later the cowbird had not laid any more.  Blue birds seem ok with some human proximity.  I’ve read they won’t nest closer to each other that 100 yards, but young siblings help raise successive fledglings.  Flying blue streaks, the most intense glimpse of one of the greatest blues.   More info in the Audubon Handbook on Western Birds.