A japanese coturnix quail cock will grab a beakful of his mate's head or neck feathers (he prefer head feathers) and holds on for dear life while he attempts to mount and mate the hen. Meanwhile, she's usually not taking this lying down... she often is attempting to do the famous 'walk-away' maneuver. It sometimes looks as if they're fighting, but if it's a cock and hen, then they're not. I have witnessed a dominant cock force a subordinate cockerel into submission in this manner as well, so don't assume that just because one is mounting another that the submissive bird is 100% female... it could be that your dominant cock is asserting his authority and avoiding eventual power struggles. It's not a good idea to keep more than one sexually mature japanese coturnix quail in the same enclosure unless you have something akin to a quail mansion, as eventually, one of them will end up scalped. And speaking of scalping, it occasionally happens that a cock will accidentally scalp his mate; should this happen in your up and coming flock, don't panic. Clean the wound and smear some triple antibiotic ointment without pain relief on the exposed and horrible looking wound. Usually healed in a week or two, and feathers return gradually over time. Normally wouldn't mention all this stuff, but since you've got eggs in the 'bator, it sounds like you're on your way to having a flock soon.