Introducing New Chickens to Established Flocks - Chickens in a Minute Video - Backyard PoultryAdd to Favorites Once chicks are fully feathered, they are ready to stay outside. But introducing new chickens directly into an established flock can be rough. How Can you be Successful Introducing New Chickens While Ensuring They Stay Healthy? First, make sure newbies are old enough to be outside and big enough to fend off bullies.