This is a scene played out many times, by the same players, in a rookery. They enforce an invisible line.
The Great Blue are there first, they start early in the year. The Egrets take the next best spots available. They can be very close in a prime nesting tree.
Egrets can be a danger to the young Herons. Adult Herons can ignore the the danger until it’s pushed.
While Herons are bigger the Great Egret is a violent predator.
Once the Egret has established it’s nest they will stand up to the Heron. Both adults rarely step over the line once a territory has been established.
Here the Egrets had taken up nesting a little higher in the tree than the Heron, who were not happy about giving up the high ground.
As usual it was all flapping and squawking. As long as the Egret keep a distance from the juvenile Heron all is fine.