This is a common problem with an injured bird. People pull them, they heal up, and then it is a wreck when they try and reintroduce them to the flock. Introducing a single strange bird is the toughest one to do, unless it is a full grown rooster as in about 6 months old+.
The solution is to introduce 2-3 birds at a time. Add a lot of hideouts, have multiple feeders and watch. Often times it is not the whole flock, but rather leaders that attack, and followers that join right in.... SO
Watch your flock, throw out a good treat - a distance away from the group. You don't want the birds that get there first or last - those are the dominant and lowest birds, you want one in the middle of the pack. Introduce that bird to your house bird. That is one on one, and while there will be some bluster - it should be pretty even and quickly work itself out. Wait 3-4 days. Now go back, and look for two more birds - from the middle - add that pair to the other pair. If you can do this in a sectioned off place in the run, where everyone can see each other, it is good. Wait 3-4 days.
Leaving the sectioned off area (which is a handy thing to have) let the foursome into the flock and watch. If it is just bluster - let it go, if there is a heartless 2-3 older bird, catch them, and put them in the sectioned off area, for a couple of weeks.
The part about your numbers....16 eight week old chicks with 3 roosters are going to be a problem in the future even if you get this to go well. A couple of points about roosters.
- being raised together has almost no influence on rooster behavior
- the darling chick often becomes the nightmare, so being a pet at 8 weeks can be an aggressive dangerous rooster at 5 months.
- roosters become interested in sexual contact and dominance long before the pullets are ready, and can run the pullets ragged - sometimes killing them
- While flocks can have multiple roosters - they tend to do much better with a single rooster - the more roosters you have, the greater chance of a violent wreck
- Multiple roosters work best in very large flocks - say 25-30 mature hens, not same age pullets
- Multi generations of roosters work better than roosters the same age. People refer this to a father/son age group, meaning one bird is 1 year older than another, and the youngster was raised up under the rooster
- If you have children under the age of 6 I recommend no roosters. Roosters tend to attack children first, and smaller children will take that attack in the face.
Mrs K