Quarantine is not optional
However healthy new hens look, house them completely separately for the first few weeks — different airspace if you can manage it, and always tend to them after your existing flock, not before. Use the time properly: watch appetites, droppings and breathing, listen for sneezing, and look closely around the vent and under the wings for lice and mites and at the legs for the raised scales of scaly leg mite. A surprising number of flock disasters arrive as a healthy-looking hen carrying something, and quarantine is the only stage of introductions that protects the birds you already have. It also lets the newcomers settle, eat confidently and get used to your routines and voice before they have a whole flock to contend with.
See but do not touch
Stage two is a pen inside the run or a sectioned-off corner behind mesh, where the new hens and the residents can study each other for a week or so with a barrier doing the policing. Feed both groups either side of the same stretch of wire so they eat 'together' daily — shared meals through mesh do a lot of quiet diplomacy. Expect fence-line posturing, raised hackles and loud opinion from the senior hens; that is normal negotiation and it burns off a great deal of the aggression that would otherwise land on the newcomers' first free day. Swap a little bedding between the groups towards the end of this stage so smells become familiar too.
Mix towards dusk, on open ground
If your birds free range, let the first physical meeting happen out on the grass, where a hen who is chased can simply run away and keep running. If they live in a run, enlarge the meeting space as much as you can and put the newcomers into the coop after dark, lifting them onto a perch while the flock is torpid; chickens wake up surprisingly willing to accept that the birds on the perch beside them must belong there. Be present at the next morning's pop-hole rush, because that first scramble out of the coop is the day's flashpoint, and have the sectioned pen still available as a retreat for anyone overwhelmed.
Resources and escape routes decide how rough it gets
For the first week, double everything: two feeders and two drinkers placed out of sight of each other, so a senior hen cannot guard the only breakfast. Scatter feed widely rather than serving it in one defendable spot. Make sure hiding places are not dead ends — a newcomer cornered under a coop with one exit will get hurt, while perches at different heights, shrubs and open sight-lines let the low-ranking birds route around trouble. A hen who can always leave an argument rarely has to finish one.
Normal squabbling versus step in now
Chest-bumping, brief chases, a single peck that settles a question — that is the pecking order being written, and interfering usually just restarts the negotiation. Step in when blood is drawn, when one hen is pinned and pecked repeatedly, or when a newcomer is too frightened to come down and eat or drink; separate the victim into the mesh pen where she can still see the flock, and slow the whole process down by several days. A wound that keeps being reopened needs separating and attention the same day, because hens are drawn to peck at red, damaged skin. Putting those two daily watches into KinsLe's Care Teams, against named people on a rota, means the integration week's most dangerous hours are covered by someone specific every single day.