Chickenstock is rapidly approaching and I look for this year to have a much larger turnout than last year. Silly Chicken was kind enough to make a wonderful poster and if you click on Chickenstock in my signature line and then go to page 2 post 13 you will be able to print the poster and hang it in your local feed store or on your refrigerator to help you remember how soon it will be here. Also check the other links for buy/sell/trade, attendance, and potluck signup.
Intergrating birds into your flock is always a stressful time for both us and the birds. I've found the flock more accepting of new birds if they are placed in the coop after the birds have gone to roost. However, often for several days you may still have fights. This is particularily true if the new bird is of a different color than the others. The oft sited phrase "birds of a feather flock together" could probably be further modified with birds of the same color feather. You may have to remove the new bird and try again later. I usually make sure I am "up with the chickens" to watch for trouble. With most flocks one hen will be the dominant bird that goes after the new one. Some times removing her for a couple of days will ameliate the problem. This often changes the flock dynamics and when you place her back with the flock she will no longer be the dominant bird.
Probably the situation most prone to disaster is placing chicks in with the general population. This is where size does matter. Chicks haven't learned the survival techniques to avoid the larger birds. While some flocks may accept new birds or chicks without a problem many more won't. Just because they may have watched the chicks for weeks doesn't mean they won't consider them to be lunch. I personally don't add chicks to the main flock until they are at least 14 to 16 weeks old and their size more closely resembles that of the flock.
Bantams, inspite of being much smaller can often co-existist with larger fowl due to their more aggressive behavior and will often be the dominant bird of a mixed flock. If it is absolutely necessary to add much smaller birds, a temporary dividing fence with a mesh size too small for the large fowl to pass through can be erected in the run to allow the smaller birds a sanctuary.