Chickens showing more aggression to each other - Why?

[binders]

I have noticed that my 7 pullets have been facing up to each other much more often these pasted few days. They just go at each other face-to-face with their hackles up and heads high. They don't seem to do anything lke feather pecking or anything. They will run up to another chicken and they will face off. Why are they doing this and why did it seem to start all of a sudden? They are about 21 weeks old and I have had them for 2.5 months so it is not like they are new to eachother. They are not laying yet and I was wondering if it has to do with them about to lay. I have seen no squatting or checking out of the nest box and all their combs and wattles are still fairly small and still pink.
Why are they sizing eachother up now?

 

[CMV]

They are maturing and trying to find their place in the grand scheme of things. Perfectly normal. Try to stay uninvolved as much as possible and they will work it out amongst themselves. If things go as they should you will have a strong cohesive flock where everyone knows where they fit in.

Good luck.