How old should they be before adding new pullets to the flock?

[VaM715]

I have some that are 11 weeks old and some that are 9 weeks old. They are housed beside my adult birds. When can I put them together?

 

[MissPrissy]

I am replying with the same post I just made this morning on another thread.

The chicks need to be close to the same size as the adult chickens before trying to mix - usually around 16 weeks old.

At that time put them in a small pen in the same run so the older chickens can get used to them but can't get to them. In about a week go out at night and put the new ones on the roost with the older ones. They will all wake up together and not realize the change. There will be some squabbling and fights but the pecking order has to be re-established and that takes time. The new chickens will be big enough to defend themselves and fight back.

If you put younger smaller chicks out with the older ones several things can happen. They won't be big enough to defend themselves from the attacks that will come from the older birds while establishing a new pecking order. They can be bullied and starved to death by the older chickens. If they are really small they can be killed out right by the other chickens.

https://www.backyardchickens.com/forum/viewtopic.php?pid=586460#p586460