thanks alot for your help.
I've got lots of other fish in the tank: starbae corys, silver dollars, clown loaches, spotted puffers, underwater frogs, clown loaches
I don't think I can create any hiding places that will only be big enough for the smaller one, but I will try to create more places to hide.
I'm not sure what you're getting at, with regard to their mouths closing, but I would say that I've had aggressive fish in the past, but I've never seen any fish picking at another one so aggressively and incessantly. The smaller one has been pressed against the filter intake nonstop, and still seems to be very much alive; and as soon as it swims away from the intake, the other parrot swims across the tank directly to it and repeatedly swims into it, pecks at it with its mouth (though not biting it), and pushing it against the walls of the aquarium.
Based on this behavior, it seems that creating hiding places may not suffice to protect the smaller parrot. Any other (alternative) ideas? Would it help if I split them up temporarily (e.g. with a wall down the middle of the tank - Is that possible?)?
thanks again for your help.