This gallery is best seen by hitting F11 and then next. The display/fight lasted about 30secs and neither bird seemed hurt afterwards, despite a couple of good nips, as one retreated and flew off after the last picture. Someone sent me this from Birds of North America.

Behavior/Agonistic Behavior/Communication interactions:
"...The most spectacular display given by herons on the foraging grounds is
the "Upright and Spread Wing" display given when two herons approach one
another; neck is nearly fully extended and tilted slightly over the back,
head and bill are held above horizontal, wrists are drooped or held away
from the body exposing the black shoulder patch of the adult. Sometimes wing
nearest the opponent is drooped lower than the opposite wing and body plumes
are erected. As opponents approach one another, head and bill are raised
closer to vertical and the neck extended farther over the back. These
displays usually cause the two herons to move apart but occasionally bring a
chase. This display is sometimes directed at gulls, Great Egrets, and even
people."