The nominate race 'nivalis'. breeds from Canada and Greenland via Scotland to Scandinavia and NW Russia. The second race is 'insulae' which breeds in Iceland (and has been cited as a perhaps rather unlikely candidate for a split). The rarest race to appear in Britain is the NE Russian and Siberian race 'vlasowae'.
Most of our birds here in North Wales seem to be Icelandic 'insulae' birds. Mike Young-Powell has an excellent article which goes into more depth about the matter here:-
From the pics below, the main distinguishing features needed to separate the two races can be seen:-
- frostiness to the mantle and back
- base colour of the rump
- colour of 9th primary
- amount of contrast in the tertials
- shape of tail feathers