Another small passerine to discuss the origins - like the White-crowned Sparrow - with some nice shots in the UK stop press.
Thought I would use the much nicer 'old' term in the header to denote the nominate northern and north-eastern breeding birds, as its much nicer than the generic term Dark-eyed Junco. This, according to my Howard and Moore world checklist, includes 16 (yes, sixteen!) subspecies, though thankfully Sibley chucks them all into groups: Slate-colored, White-winged, the lovely Pink-sided, Oregon, Grey-headed, Red-backed, plus Canadian Rocky Mountains.
Have there been any studies of these? I wonder if they may be re-split any any stage....