quaker parrots and other parrots/birds in a aviary

Hello Uaker and welcome! If the aviary is multi-part, I think it would be ok to keep the birds that don't suit as it's always stressful to rehome birds anyway. A young parrot goes through an average of 7 homes in its first 10 years because people often buy them without understanding what it means to keep a parrot, so, in my humble opinion, it's always best to move slowly, seeing each bird as an investment and a living creature you have made a promise to take care of, rehoming where you feel that would be best for that particular bird, and taking care to find said bird a responsible and caring owner. I'm sure you know all this and I'm sorry if I'm telling you how to suck eggs, I think we always worry when we have birds that we have a responsibility to the species and to other pets to make sure they have the best lives possible!

I would maybe stagger getting new birds though. Start with one, just to see how Polly reacts. Bear in mind that it may take Polly a long time even just to tolerate a new bird, so keep them in separate compartments for as long as you can to help Polly get used to the new addition. You can gradually add new birds as Polly gets used to the sight of them. It may be that Polly does not take to new birds at all and always needs to be in her own compartment. Being a pet, she is likely to still need a little bit of human contact to keep her happy, but having other birds around her and not being in complete isolation is likely to help keep her healthy, even if she is not in the same compartment. Seeing them and being able to communicate with them will still afford her some company if she is too frightened or bullish towards them to keep her in with them safely. I have not been a bird owner for very long, so others may have better advice or contradict what I've said. They are likely to know best!

I think the key is slowly, slowly, slowly and a bit at a time. Definitely don't go out and buy four or five birds, hoping that Polly will take to them. That might be a bit too much for her and set you back. In my experience (and I only have one quaker!) Conures are a good alternative bird species to keep as companions for Quakers. Maya (my quaker) made friends with a sun conure at the shop where I bought her, and whenever I take her back to board he is the first bird she looks for. Be aware that, with birds that size, if you have one of the opposite sex to Polly, that may result in a pair bond and Polly may lose her tameness, which your son may not thank you for when he gets home! At least a little time spent with you as often as possible will help to keep her human tame. Conures are also very loud birds, so ascertaining how sensitive your neighbours are to noise will likely be crucial. I would suggest that you research into the general temperaments of different bird species before buying new ones. For example:

Quakers are very assertive birds who will push others about to get their own way. A cockatiel however, despite being roughly the same size as a quaker, will tend to be a very laid back bird. They may suffer at the hands of other birds because they don't tend to be as assertive. Budgies have been known to bully cockatiels, who are generally very sweet natured birds. Obviously, every bird is different and there will always be exceptions to this rule, but knowing as much as you can about the species of bird you are buying before you buy it will really help. As I said, I am by no means an expert as I only have Maya and she has only been with us for 7 months, so if others contradict my advice, it's best to listen to them because they will have years of experience and knowledge on me. Best of luck, though!