Although I don't want to set human sentiments on birds, it really seems like there is some jealousy going on. Most certainly with Shade. Why would I say that? Normally twice per year she gets a bit distant. I think this is normally when hormone kicks in and this generally always happen in late fall/early winter and in the spring. Instead of getting mean, she just gets a bit more independent and a bit more grouchy with the other birds. I've noticed over the last week or two that she's been getting in that "mood" - she doesn't want to cuddle as much and just does her thing. Having "competition" around has made things interesting. Just like yesterday, although she was perfectly content being on on her own, the moment Nemo showed up she had to show that she was #1 bird. She's been doing the same with Pixel lately as well - I normally take Shade first then move onto Pixel and when offering to Shade to spend time with me, she either doesn't come over or steps up, stays on my shoulder for 2 minutes and then flies off, at which point I go and get Pixel. But the moment I have Pixel on me, she wants to be there. I've had Pixel since June and while it was bit of an adjustment for Shade for the first week or so, that routine (Shade first, Pixel second) worked fine.
While a lot of birds get aggressive when hormones kick in, I just never saw this with Shade. Even now, it's not outright aggression anyways. At this point, it just seems like she's more insistent on letting all the other birds know she's "head bird" when it comes to me and she does this by insisting to be on me when others are and being rather possessive of my shoulder - not by showing any aggression to myself, quite the contrary, she cuddles as close to my head as she can and will.not.budge.