This cracking bird is ringed with a metal ring, with a protruding clip, on its right leg. Rings of this type are used in Poland, Ukraine, Russia, Belarus and Estonia (per Ronald Klein). Most Polish rings are on the left leg, but occasionally mistakes are made, so all we can say is that it comes from one of these countries. The 3rd picture is the same bird at Grunty Fen on 6th December.