With no parents in sight anywhere and feeling some urgency about getting care for this one, I scooped it up and we created a little homemade nest out of paper towels and a tiny wicker basket. I picked up a small canister of baby bird food on the way home (a formula mix similar in consistency to human infants' mix-with-water stuff) and hand-fed it every half hour or so until I could locate a wildlife center (at our county Humane Society) who would know far better than I how to best care for the orphan. Little bird is there now, as is the baby bird food which they can use to feed it and others; no doubt they'll be far neater with the hand-feeding than was I.
I'm starting to see this mourning dove/bird pattern emerging in my daily life. I wonder what that's about.