I just experienced a similar fate as southdakota, 64 of my three week old Jumbo Brown Quail were moved out of the brooder to their pen last night. This morning after mowing the grass I was checking all my birds and in the corner of the pen was a 4ft black snake with to quail size lumps. Needless to say that snake will not be eating any more birds.
Only redeeming factor was it was 2 males which I have to many of anyway. I'm certainly glad it wasn't any of my BLR wyandotte chicks in the hoop house near by.
I've read a number of posts on snake proofing, and it seems the only solution is to rat wire the complete pen. My quail pen right now is a 16 x 20x 8, though this more than large enough, I've never liked crowding my birds. Has anyone else tried another deterrent that works?