you can get several spicies of quail verry fast flyers tricky little bliters to shoot, and yes i think its ilegal to release no native spicies into the wild you probly wont hold them in cover crop as soon as most combinable crop is cut they will feck off never to be seen again, you do get wild common quail (europian) around at the moment but will migrate again around the end of aughust.
smart little birds but a lot off effert i think just to loose them in a few weeks only my opinion but a wast of time make a pen a keep them in that