Another thing to bear in mind regarding an extinction burst: Behavior that has been reinforced at random, unpredictable times is harder to extinguish than behavior that has been reinforced regularly.
It sounds like you are doing the right things to try to extinguish the screaming.
Some screaming is due to it getting the bird what it wants. But there is also some screaming that the bird does for its own (unknown to us) reasons. So, not all screaming can be extinguished. But it should be able to be lessened.
I sound like I know something about animal behavior, and it's funny, because I learned a lot about it in college. It's applying it that is the problem though. I mean, look at how unsuccessful I have been with Emma.
In the movie, "Out of Africa" one of the characters (a native African tribal man) says to Meryl Streep (a Dutch woman who wants to teach the African children to read), "the English can read, but what good has it done them?" That's how I see my ability to actually apply what I have learned. However, I shall certainly keep trying
