No matter how much we love our chickens, there are some undeniable facts that we all need to face from time to time:
Therefore, if you want to maintain a nice supply of eggs, on occasions, you will need to introduce new chickens to the flock.
Now I say this in the most loving way, but:
Knowing and understanding these two points can help us introduce new birds to the flock.
Simply "dumping" new birds into the flock can result in significant stress to both old and new chickens, ultimately resulting in less eggs, and injury and stress to the birds - all of which impacts on the reasons why we keep backyard chickens in the first place.
I have often used the following process to reduce the stress on the both old and new birds with a high degree success:
Fence off a small area within the chicken run. In the morning, place the new birds within this fenced-off section. Ensure that the new birds are visible to the older chickens, but not physically in contact. The intention of this step is provide opportunity for new "friends" to become familiar and acquainted with each other.
After sunset, when old chickens have gone to roost in the hen house, physically place the new chickens on a roost in the hen house. However, as much as is possible, ensure that they not directly beside an older chicken. Also, ensure that they are placed on a roost below the others.
Word of warning - while your new chickens are still fenced off from the old chickens, ensure that they are secure; ensure that there is also a cover on this section. If you don't, there is the risk that when you come to find them, they will have already flown out to find somewhere else to roost.
In the morning ensure that they have plenty of room to escape the attentions of the older chickens - do not force them to spend time in direct contact with the older established members of the flock. If you allow them to "free-range" ensure that the run is open.
At the end of the day, check on them. It is probable that they will return to the hen house to roost, but check to ensure that they have. If they haven't (although this is unlikely), repeat the proceedure of the previous night.
For several days, keep a close eye on them and ensure that they are settling in well. Check that they are able to access food and water adequately.
Remember, when you introduce new chickens to a flock, they do need to establish their "pecking order". There is nothing you can do to prevent this, but hopefully the above steps will help you reduce the stress that can sometimes be put on chickens during this process.