What could be causing this behavior - 3 year old hen attacking 4.5 month old pullet


11 Years
Jul 10, 2010
southern AL
I have 5 chickens.
1 - is a 3 year old buff orp. She had friends, but the fox took them 2 years ago. (she's been hanging with the ducks since then)
I added 2 new chicks this spring (late Feb), a barred rock and a black sex link.
They have been sharing a coop for 2-3 months with no issues.
They free range. When they are penned up, they have been fine together.
The other 2 are 11 week old chicks that aren't in the coop yet (they are still tiny and not sure if they are both boys or not - if so, they go back to the breeder and not worry about integrating into the coop), but have started to free range.

My issue - existing 3 year old BO is now mounting and then basically attacking the BR.
BR started laying a week ago.
3 year old BO has stopped laying in the box. I see evidence of an egg under the roost in the morning - shell gone, but still some yolk and white there - when she drops an egg during the night, so usually eats the shell and some of the yolk.
After the BR lays each morning, the 3 year old runs into the coop and sits on the egg for a while.

Today 3 year old BO mounted the BR. I plucked her off when she jumped on and started pulling feathers from her head. When the BR was walking way, the BO ripped feathers out of her butt and ate the feathers.
Then when we left this evening, we locked everybody in the pen. DH put the BR in the pen and the BO immediately thumped her on the back of the head and then grabbed feathers. BO was in front of the BR, not mounting.

Is this all linked?
Do chickens get possessive? When I had the original 3 chickens, they all shared the same nest box no problem.
We grabbed another nest box tonight, so I'm hoping maybe this will make it better.

Any ideas?
I would remove the bully for a week or so to change the pecking order. The young hens now are maturing and the bully hen is trying to keep her position as head bird. Chickens are mean. Once you add in the new young birds and the flock gets bigger she should settle down. The more chickens, the less conflict. Another nest box really wont make much of a difference if they all like the same nest?
Makes sense.
Added a new nest bin anyway and will keep an eye on interactions and if it escalates, we'll separate her out during the day.

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