Rare Goose and Cranes - of suspect origin?

Down south seeing relatives, I couldn't resist driving a little further down the M5 to have a wander round Slimbridge. I hadn't expected to see Red-breasted Goose or Common Cranes and got rather excited until I reminded myself how close I was to the captive bird enclosures. This said, the RBG and the 13th Crane (only 12 had been reared and released here) were both unringed. Who knows where they'd come from...