Rose and Dorian have been going through the same "dominance / territorial" stuff since early this year. I think they are about a month or two younger than Chica and Loca.
I have found that cutting back on the protein in their feed seems to help (they don't act up as badly unless they manage to get into the sweet feed or oats).
Paco who is the same age has gone into "baby sitter" mode though.. he left their normal pasture and cleared several 6 foot tall fences to get in with the babies.. has never shown any aggression towards them or the ducks/geese/rabbit that share the "baby pen" even though he, Rose and Dorian are all the same age.
As a note.. Rose is the only female of the three.. it started with her strutting and booming.. then Dorian chasing her up and over a fence... then her chasing him up and over a fence... and back and forth. When I cut back on the protein they decided to settle down a bit. Rose still struts and booms.. but the major fighting and chasing has as much as ended. Now it's just a short chase by either one and then going about their business. (which is good because i am still surprised that they can clear a 6 foot fence when they have a mind to).
As to if it's "pre-breeding" behavior.. I think it's more of a hormonal issue.. growing up and figuring out that they are soon to be "adults" which may or may not lead to actual mating and egg laying this fall. The normal egg laying of captives should start around the 18 to 24 month time frame anyway... (well, at least down here in Texas it seems to be the norm). So it may very well be the birds coming of age to start thinking about laying and nesting. Now as to if any of them will find a suitable mate among their flock is another matter. Since they basically grew up together they may look upon each of the other emus as siblings and not potential mates. Time will tell
