I’ve filmed the Great Blue Heron a number of times here in the park, but I’ve never heard it vocalize. Here, for no reason clear to my human eyes, this Blue let out with his call, or song, or warning — whatever it was. I saw no other herons any where in the vicinity, no possible rivals of another species, and nothing in the way of prey. Maybe sometimes a bird just wants to sound off for no particular reason.
My little video repeats the scene twice, first at normal range and volume, then zoomed in with audio boosted.
The Cornell Bird Lab website features a selection of Great Blue vocalizations; click it here.