I don’t think you would get any argument from any bird owners about the necessity of quarantining new birds to your flock. The problem often is – how to do it!
If you quarantine the new bird in your home, it can be in a different area completely away from your other birds, but the air will be shared. Airborne diseases can travel from one room to another by way of the furnace & air ducts.
The quarantine is used not only to protect your current flock from the newcomer, but also to protect the newcomer from your current flock. You must wash your hands and change your clothing between looking after your other birds and your new bird.
A better solution would be to house the new bird in a completely different building, but most of us do not have access to a separate building for quarantining birds. If you have a neighbour that enjoys birds, but does not have any, perhaps he would be willing to allow you to quarantine your new bird at his residence.
How long should the quarantine period last? You will receive different answers to this question from different experts ranging from 30 days to 90 days – with 45 or 60 days being frequently suggested.
Most people are going to opt for the quarantine in the home in a separate room for about 45 days. They may take the new bird to a veterinarian during this time for a checkup with blood tests. If everything checks out ok and after the 45 days have past, it should be fine to move the new bird in with the rest of the flock. Of course depending on the type of birds you have, each one may be in their own cages or in a community aviary.
After many years of pet bird ownership, I have decided to write e-books about the care of some of these wonderful birds.
Amazon.ca has a great book you can check out at Guide to Companion Parrot Behavior.