Nesting pair every May, including this year. BUT June 23 first time ever two additional green herons showed up early evening. "Visited" original pair's nest (in tree above our pond). Great fuss and bother - vocalizing, flying around. TWO different people counted four in the air at one time. WHAT'S GOING ON? Could new nearby pond formed by new beaver dam be relevant? But there's LOTS of woodland, water, etc. - why a "fight"?