Don found a Great Horned Owl eggshell yesterday. This solves a mystery and opens a new mystery. The brown egg is from one of my chickens and pictured to give a better idea of the owl egg size (my chickens lay large eggs, not those wimpy "large" eggs you buy at the grocery store).
The mystery solved is why we haven't been seeing our hawk at the nest in the edge of the yard. Turns out Great Horned Owls will run a hawk away from their nests. Great Horned Owls are lazy - they prefer to take over someone else's nice cozy nest instead of building their own. We miss our hawk, but there's not much we can do about neighborhood politics. This eggshell was found on the ground below the hawk's nest, which is obviously now an owl nest.
Anyway, the NEW mystery is whether the egg hatched (now is the right time for it to hatch) or did another mean neighbor, say one of the crows, eat this egg? There's no sign of broken yolk, which is something we see when the crows get a chicken egg (they make a mess). I'm going to be optimistic and assume we have baby owls snuggled up in the old hawk nest at the edge of the yard!