Ermines turn white during the winter, with only the tip of the tail remaining black. However, in the southern regions of the ermine's range it clearly doesn't get so white. Encyclopedia of Life says that:
However, in the Netherlands, the animals are often only partially white.
Ermine's range is clearly much more southern than the Netherlands:
So I was wondering where does the border go, north of which the ermines are completely white and south of which they remain more brown? I understand it necessarily is not a clear cut line, mountains have impact and subspecies may differ, but I would assume someone must have mapped this. Or is it just weather related, will a southern ermine turn white if the winter is really cold?
I'm just asking this out of curiosity, but the question is rather relevant. Ermine pelt has a long history as an important trade item, and the most valued pelts must have originated on the white side of this line.