Introducing New Birds
When adding birds to your flock a new pecking order needs to be established. Hens can be very territorial and see any addition as intruders (unless, of course, you have a rooster who usually is happy to welcome new members to his harem).
It is prudent to keep the new birds separately for a fortnight. Ideally they should be able to see each other during this time.
Keeping new birds away from the resident hens serves two purposes: quarantine and a higher likelihood for a positive integration.
Quarantine is not only recommended to protect the resident birds. The new birds may not be immune to diseases your birds are immune to. A slow integration prevents the birds from suddenly being exposed to large quantities of infective material and they are more likely to be able to develop their own immunity without ever showing symptoms.
It is good practice to dust new birds with a lice powder like Diatomaceous Earth (DE) or a dog flea powder which is available from supermarkets and outlets that sell animal health products.