Why thirty days is the working standard
Many of the illnesses that move between backyard flocks do not show themselves on the day a bird arrives. A hen can look bright at the seller's gate and still be incubating a respiratory infection, be carrying mites beneath her leg scales, or be shedding something her new flockmates have never met. Two weeks of isolation catches the fast-moving problems, but a full month gives slower ones time to surface, and it gives you a proper window to watch the bird eat, drink, lay and behave across a laying rhythm. It also lets a stressed newcomer settle: transport, new feed and strange surroundings suppress the very signs you are watching for, and many birds only show what they are carrying once they relax.
Setting up a quarantine space that truly separates
Quarantine only works if the separation is real. House the new birds in a pen or coop that shares no air, drainage or equipment with the resident flock — a separate outbuilding is ideal, and at minimum a pen at the far end of the property, downwind where you can arrange it. Give the newcomers their own feeder, waterer and cleaning tools, and resist lending gear back and forth. Work through your chores in a fixed order, resident flock first and quarantine birds last, and wash your hands and change boots, or use dedicated footwear, between the two groups. A single shared wheelbarrow of bedding can undo the whole exercise, so treat the quarantine pen like a separate little farm.
What you are watching for during the month
Check each new bird daily, hands-on where you can. You are looking for sneezing, rattly breathing, discharge from the eyes or nostrils, a pale or drooping comb, watery droppings, feathers out of condition, and any bird sitting fluffed up and apart from the others. Pick each bird up once a week: feel along the keel for lost weight, part the feathers around the vent and under the wings to check for lice and mites, and look closely at the legs and feet for raised, crusty scales. A bird that eats and drinks heartily, holds her condition and shows none of these signs across the full month is a far safer addition than one waved through on day three because she looked lively.
Ending quarantine and mixing the flocks
When the month passes clean, introduce the newcomers gradually. A week separated by a fence line lets both groups trade looks and postures without fighting, and most keepers do the final mix at dusk or on neutral ground with extra feed stations spread out so no bird has to compete hard on her first day. If anything suspicious appears during quarantine — a respiratory noise that will not clear, parasites you cannot get on top of, a bird steadily losing condition — extend the isolation and have a poultry vet look at her rather than mixing and hoping, because one sick arrival can run through an entire laying flock within days. KinsLe's Pet Passport holds each arrival's quarantine dates, your daily notes and any vet findings in a single portable record, so when a new hen finally takes her place in the flock, her health history travels with her.