I answered, in a rambling way, a question posed to me in the comments of a previous entry by Sonja, and thought I should expand my answer a bit.
Bird-on-bird aggression is a real problem, and can have severe or even fatal consequences. As I wrote in the comments, I know several birds who have had their top beaks removed by another bird, many birds whose toes have been removed, and at least two that have been killed by other birds.
We are extremely cautious in our house when it comes to Daphne, as she is so much smaller than everyone else and could easily be harmed. When she comes with us into the kitchen, I have her perch in a place where the other parrots can't access her. She is never allowed out of her cage unsupervised, not even for 30 seconds if I have to grab something in another room. If any of the parrots had ever shown aggression towards her, we would implement even stricter policies to ensure her safety.
We are careful when it comes to our other birds as well, but not to the same degree as we are with Daphne. They are similar size so the threat of serious harm is less (although certainly not eliminated). Beeps, Max, and Calypso all can fly to avoid a confrontation, and Kika will be there soon. We know their personalities and feel comfortable with the risks that we take. Rocky has never made any sort of aggressive move towards another bird (towards me -- that's another matter!)
Calypso and Max are allowed to go on each others' cages. They've worked out a system that works well for them, and have been doing this for over four years. Usually Max flies over to Calypso's cage and either plays with his toys or eats his food. When Calypso has had enough of this, he takes a few steps towards Max, and she flies back to her cage.
Any other parrot that goes on another's cage is immediately removed, and they rarely do that anymore as they know it's not allowed.
Max and Beeps will occasionally get into a little tussle, but this appears to be play-related, and I intervene if it lasts more than a second or so. They take turns instigating, so one isn't stressing out the other.
When Kika first came to live with us, Max buzzed her, but this stopped after a few weeks, and hasn't happened for months. Max also will occasionally buzz Rocky, but usually only if he's on Thomas's shoulder, as she knows that's generally not allowed. This happens about twice a year.
There are no friendly interactions between my parrots. Even though I tell the caiques it would feel better if they'd allow their fellow caique to preen the pin feathers they can't reach, they don't listen and they're stuck with my human fingers trying to do the job.
I guess the point of this is to explain how things are in our house, and to reveal some of the thinking behind what we do. I would hate for anyone to stumble across this blog, or the pictures, and think it's ok to allow a bunch of flighted parrots to roam their house unsupervised. Serious damage can occur, and these wild animals depend on the humans in their house to keep them safe.
In updates on other things I've written about lately, we have finished all 9+ pounds of strawberries. Yum! I was able to find all three of the baby fish this morning. I feel even more certain that they are Australian Rainbowfish, and that the largest will survive. The two smaller ones probably will survive also, but I'll feel more confident of that in a week or so when they're a bit larger! And we still haven't made a decision about Kika's name. Maybe we'll just keep it because I can't find one that I love.
We're having visitors in a few hours, so I'll be back in a few days with posts about how the parrots behaved. I'm hoping Max will do her clicker routine, but sometimes she doesn't like to do it in front of people.