I've been dealing with jealous birds lately, and the biggest case of "jealous bird" is Piper.
It appears that if I'm scractching another bird's head, he feels he must get his head scratched to. If I'm remotely paying any attention to someone else, he'll try to put himself in the middle. I think he's also started to do this with the Boy, although in the past he recognized that Petey and Joey might get more attention.
Latest example of his jealous ways? Came this morning. He originally was on my left shoulder and Shade on my right. Shade moved onto a glass of water and Piper placed himself between Shade and myself, on a pillow I keep handy between myself and the desk. When she was done with perching on the glass of water, Shade was coming back towards me, so I scooped her up and placed her back on my shoulder, as Piper was getting agitated. She wanted back down so I moved Piper back on my shoulder while I tried to deal with Shade. She made it to the pillow, which made Piper go nuts and determined to go back. I had to move him three times before I finally could Shade (who was peacefully sitting whereas Piper was intent on attacking). The moment Shade was removed, he didn't want to be on the pillow anymore. Absolutely no interest.