Thanks for the input exop. I think you're right about the genetic aspect.
Do you put mixed age roos together, or is your group all one age range? I would like to have a bachelor pen, but I don't think it works like I want it to (in my head).
They will scuffle, if you're there or not. It's just how they establish order - as long as there's no bloodshed. That's fighting, and you should break it up.
My roos ( French Marans and Ameraucana) get along very well (bizarre!). They are almost a year old and daily they "do the dance" and...
The cockerels jumping at each other is normal, sorting out the pecking order. Do they have plenty of space? - They're not too cramped together? Make sure the less dominant birds have a place to run and get away (I used 2 large mason blocks and log to create an obstacle/roost in the run), plus...