I have 3 parakeets and when they were first settling in with each other there was a bit of feather-pulling going on as they figured out who was 'boss' of the flock. But they're really mellower now, and don't do that any more ... maybe it just will take time for them to get used to each other. I always start the new bird out in a separate cage, and then let them get used to each other, so I think that really helps.