The nest is delicately balanced between two branches of one of the saw-tooth oaks Adam planted at the edge of the yard eight years ago. At just-about eye-level, I have to ease up onto my tiptoes a bit for the right angle to see into its depths, to make sure that it is empty. It could not be more symmetrical if its avian architect had used computer-aided drafting — a cup-shaped scoop of twigs and thread-sized roots perfectly built for what? two eggs? three?