Illusion is right....here in neb in the 70 s the quail were thick...we would jump coveys with 25-30 birds pretty much everywhere...
I could not hit one to save my life back then...I used a bolt action 20 with a pretty tight choke...I would stomp the grass and thickets looking at the ground when the busted they were up and out of my sight then I was forever behind....
Years later I attended Chuck Drykes shooting school back when I first started shooting clays...and found some tricks to eliminate the illusions ..first look where you think the bird will go and let it come to your vision...when in brush try to lock on 1 bird and not watch the birds whole covey ...brush is a tough game...