Nothing is set in stone and 100% predictable when it comes to chickens, but a few things that I have learned about chickens and merging flocks (IMHO):
New chickens should be kept separate from your existing flock until you can make sure that all are healthy. Quarantine at least 4 weeks.
Chicks should be fully feathered. I don't recommend merging them before they are at least 6-8 weeks old.
If you are planning to merge them after the quarantine period is over, put them nearby where they can see and smell each other, but not actually get to each other. This is the time where they get used to each other.
When merging, it is best to do it at night, while they are roosting. If you can provide a neutral territory, that helps too. (ie moving from brooder into coop where no one is entering the others established territory. A soft red light may help discourage pecking.
A friend of mine has success merging flocks when she sprays all chickens with cheap perfume or cologne, so that they all smell the same. She mixes up the groups at night, so they wake up in a different spot and with different chickens around them.
No matter what, chickens have a social hierarchy and will establish a pecking order. This happens on 3 levels. Males and Males, Females and Females, and Males and Females. Keep them under observation when this is happening, as you may have to separate them if they get too rough!
You didn't mention if these were male, female, or mixed. If you have more than one roo, you want to make sure the food and water are available in different places in the run or coop so that they can get to food and water without having to enter the others territory.
Polish chickens will frequently get picked on. Many are not as socially adept (not meant to be insulting!) as some other breeds and their top knot makes them easy targets for others to peck at.
It sometimes helps if you can provide a distraction for the existing flock - such as a head of cabbage or soda cans with pebbles in them to peck at.
I have two 10-week old hand-raised Quail D'Anvers (one male and one female), and sixteen 5-week old mixed chicks (all female except the Silkies who are straight run TBD.) While I would like to integrate the entire flock, my D'Anver roo is very protective and territorial (at least in his mind.) The female D'Anver is fine with the others. She is very sweet and very curious about the others, but I am not crazy about leaving the male alone. Two of my 4 Silkies act like "Fearless Freddys (they are probably ALL roos!)" I eventually want to breed the Silkies. My coop is not built yet and my plan is to separate the flock into 2-3 mini flocks when they are moved into the coop:
- two D'Anvers
- four Silkies + 1 white cochin (not if all Silkies turn out to be roos!)
- remaining birds
Ideally, I would like to integrate the D'Anvers with the remaining birds, but we'll see what happens once the coop is built.
Good luck and I hope this was helpful.
Over researched and made myself anxious about coccidiosis
