Thank you Geoff! That's a fantastically in depth response! I haven't previously done any shaping with this bird, but I am currently working on establishing a clicker as a bridge, which I'm hoping will allow me to mark his silence even if I'm not in his line of sight.
Is the silence something that should only be worked on indoors, or could I take advantage of his silence in the field? I'm concerned, since he already recognizes the two separate locations and screams at one but not the other, that rewarding for field silence would have little effect on his indoor noise.

Fred: I attempted and mostly failed to hood train my aplo. But yes, when hooded or in the giant hood, he will still scream if he hears me. It's not as bad in the giant hood as if he were perched out in the same room, but still enough that I usually have him in a separate room from myself either way.