I have a flock of 5 pullets that are all just starting to lay (about 6 months old). Two silkies and 3 large fowl birds. They have a large fenced in run with a coop inside. In the coop there is a roosting bar up top and a nest box off the side. All 5 birds used to always sleep on the roosting bar, but for the last week one of the silkies is sleeping in the nest box, which is divided. She hasn't gone broody because she's not there at all during the day and she's not sleeping in the side where all the girls are laying, she's sleeping in the other side. I've never noticed any significant aggression in my small flock, and if I take her out and put her up on the roosting bar she stays there and no one bothers her. Any ideas why she's doing this? It's a little annoying because she's filling that side of the nest box up with poop during the night! She seems to be perfectly healthy and is laying very well for a silkie.
Hormones, either block off the nests at night or keep putting her up on the roost until she gets back in the habit.
As in the hormones are making her go broody just at night or her hormones are making her not want to be with the others.
I would watch them each evening as they get up on the roost, she may be bottom of the pecking order and just may not want to deal with it any more. I have had hens move out of the coop due to this on two occasions, both were to bottom of the pecking order birds. Even if it doesn't seem very aggressive to you she may be intimidated.
Hormones as in.....they all just stared to lay so their hormones are a bit wacky, it can change behaviors and pecking orders.