What On Earth…

… is this?

Photo Darlene Smyth

This morning’s IBA survey was pleasant enough, but it was obvious that summer has arrived in southeast Arizona: in nearly two hours we saw not a single bird that was certainly a migrant. Of course, no reason to complain when the breeding residents include such fancies as Northern Beardless-Tyrannulet and Broad-billed Hummingbird.

Our strangest find, though, was the stone object in the photograph above. Ideas, please?