THE EYES HAVE IT!
I noticed something about the heron. It's eyes move, at least more than I had previously supposed due to that glassy stare. That means that the bird doesn't have to move its head a lot to spy prey. Well, duh, Sherry!
Here are four shots of the same bird. In the first one, the heron is just waiting; his eyes are focused forward.
In the second, he seems to notice something. He has extended his neck but his eye has moved only slightly.
In the third shot, his neck is extended and his eye has definitely rotated inward and down.
Take a look at the fourth shot taken only three seconds later. Something is definitely in sight. He is focused!
He didn't strike so we'll never know what he saw. But I learned something new and that made me happy!