Shovellers, Wollaton. Icy, raw wind with fine snow falling mid day. Watched a group of these ducks 'sifting'. Eventually they seperated into  their respective pairs and began swimming around each other in neat circles almost pirouetting to filter matter disturbed by the bird in front. They swam round and round for quite a while but were interrupted by a Mute Swan intent on chasing last years full grown young off the lake.