About 6 months after we brought Max home and after we had moved into our new house, Thomas's mom asked us if we would take her budgie, Lenny. He was quite old and was ignored in his home, except for the cats who would look at him in a menacing way. He was cagebound and not interested in people. Due to his age, we worried that handling him too much would give him a heart attack.
We brought him home and packed his cage with toys. Max was interested in the new arrival, but he didn't arouse much jealousy because he didn't require a lot of our attention.
However, the first jealous episode we saw from her did involve Lenny. Max was fledged (learned to fly) at her breeder's house, but we decided to keep her wings trimmed for safety (Max is now fully flighted, but we'll get to that later!) However, when she would start to molt, we would let her fly for a few weeks/months until she got a bit too sassy, at which point her wings would be clipped again.
Max loved to fly and land on the curtain rod that was in front of the doors leading to our breezeway. We did not like her hanging out up there, but if we went to remove her, it became a fun game for her. So we decided to ignore her when she was there. She did not like being ignored, so she would be extra cute saying, "Hello! Come here! Up!" and whistling little tunes, which made it very difficult for us to ignore her. After a few weeks of this, when Max would fly up there, I would turn my attention to Lenny and start talking about what a good boy he was. This was not acceptable to Max, who flew down from her perch, buzzing the top of my head in the process, land on her cage and exclaim "Good Boy!" (At the time, we thought Max was a boy). What a ham!