Chickens roosting on opposite sides?

[Chocobo]

I have three chickens in a tractor with a "coop" that is 4x4 and has a roost going from one side to the other.
Their whole lives they've always piled up together on one side but lately I've been noticing the "boss" is by herself on one side and the other two snuggle up together way on the other end.
I've never seen any fighting and don't think there is a problem, just curious is anyone knows why they would change their sleeping habits like this.

 

[florida lee]

I have noticed that in one coop they separate in groups at night on the roost. When they were little they all slept together. In the other coop I have some younger pullets (17 wks) and one hen (1 yr). she does not like anyone next to her so she sleeps on one side and the pullets on the other end of the roost.
they may get too hot sleeping all together.