Oh happy day! Your baby chicks are fully feathered and you’re excited to put them in the chicken coop with the other chickens. But wait! Don’t just put the new birds in the coop and assume everything will be awesome. Your older flock might not take kindly to the new birds, and there are several things you need to do to keep the younger chickens safe.
When integrating chickens, size matters. If at all possible, wait until your chicks are roughly the same size as your exiting flock. I have successfully integrated smaller chickens, but you will want to be careful and make sure to follow these steps.
In the beginning, it’s important that the two flocks of birds can see each other, but not touch. I’ve used tall dog fence panels to keep my flocks separate and it works very well. The older birds free-range, while the younger birds enjoy grass. This gives the adult birds time to sniff out the younger birds. The 2-stall hog house I used as a chicken coop for a number of years worked really well. I just kept the new birds on one side, and the older birds on the other. It’s okay if you don’t have a set-up like that, but you will need some way that your birds can sleep in separate areas. Keep them separated in this way for at least two weeks, if you can.
After a couple of weeks, start letting the birds out together during the day. Make sure you have lots of food and water options, so they don’t have to fight each other. You can also distract them with yummy treats during this time. It’s very important that you keep a close eye on them in the beginning, so the older birds don’t gang up on the younger birds. Older birds can be quite brutal and even kill new birds – so pay attention. After a week or two, if everyone seems to be getting along pretty well, it’s time to get them together in the same sleeping area.
To get them sleeping together in the same coop, it’s best to add the new birds at night when everyone is sleepy. Sneak them in and then make sure to get out there early (before day break) the next morning to get everyone out and roaming.

Successful integration of new chicks to an existing flock is not hard, but you do need to be careful and take your time. If you integrate slowly and gradually you should be able to keep all of your new chickens safe and happy.