My pen has metal, about 30 inches high along the bottom. When I have had coon problems, they always caught them in mid flight on the top and sides of pen, in which is all 1" poultry wire. They'd eat what they could, sometimes it was just the head, then drop the rest. After a few attacks, the remaining BW's seemed to have learned not to flush to the sounds of the coons in the night and would hunker down instead. Maybe the quail you have know better?.......or maybe your intruder has a full stomach and just hasn't came back for a refill yet?
Also, my neighbor has pheasants with netting on top of huge pens, he claims to have watched the hawks spook/flush the birds, grab their heads when they hit they netting, remove their heads only, and drop the headless corpse back into pen.