I would not give them salt.
I am guessing you have a crowding / boredom problem. I had this issue when I had a hawk hanging around my property and had to coop my whole flock up for a few months this winter. I never got it to stop, but it was a little better when I gave them something to do. At the recommendation of several other members I put a head of cabbage in there every day or so. I actually made a tool for stringing the heads up. I took a long skewer and cut a notch in the end of the tip, I then pushed the skewer through the head of cabage (through the core to the top, not through the side) then hooked a piece of wire in the notch I cut, then pull the skewer and piece of wire through the head of cabage, then tie the piece of wire. I hang this under a lower roost. Keeps them busy for hours.