I have heard them; I have seen them; but, this was the first time I watched as a heron called.
The Great Blue Heron is usually quiet, but when it speaks it does so with a loud low-pitched GRONK—a sound that one might imagine emanating from a Pterodactyl, some hundred and fifty million years ago.
Almost touching the lakesurface, a juvenile heron opens its bill wide and emits a resounding gronk.
Terrific photo.