This can also reoccur if they don't see you for a couple of days or their world has changed significantly. Just like a hen who has been removed for a few days, they will have to jockey for their position again. Kind of crazy to see this, considering they can be so smart in other ways!
Greetings all,
(1) Are you new to chickens / when did you first get chickens? 2010
(2) How many chickens do you have right now? My flocks have ranged from 2 to 53, I tend to raise more than I need and sell the extra off.
(3) What breeds do you have? several sex-linked varieties, NH and NJ...
If the last hen was from a commercial hatchery, they tend to vaccinate for Marek's (a live virus, part of the herpes family and it is cheap for them) which in turns contaminates your property with Marek's disease. A neighbor of ours vaccinated their birds for Marek's which spread via the wild...