The bird above showed up at my feeder this week. Many birders might call this form of Dark-eyed Junco a Slate-colored Junco and not give it another thought. Technically, though, this is not correct.
Male Slate-colored Juncos are evenly dark gray above, with no contrast between head and back. This bird has an obviously darker gray head contrasting sharply with a paler gray back that is washed with a touch of brown.
The junco above is a Cassiar Junco. This was described as a subspecies of Slate-colored Junco when Slate-colored Juncos were considered separate species from Oregon Juncos. But in the Great Lumping of 1983*, most of the juncos formerly considered separate species were lumped into "Dark-eyed Junco." Thus birders "lost" Oregon Juncos, Slate-colored Juncos, White-winged Juncos, and Gray-headed Juncos from their lists.
So if you saw a bird like this before 1983 it would have been considered a subspecies of Slate-colored Junco, and you could accurately call it such. However, since then, Oregon Juncos, Slate-colored Juncos and this Cassiar Junco are all subspecies of Dark-eyed Junco. So, technically, it is not a Slate-colored Junco. It is a Dark-eyed Junco or Cassiar Junco, but it is not a Slate-colored Junco.
I know, only 8 people in all of North America care. What? Not that many?
Looking at this level of detail will help you become a better birder--and you can do it in your own backyard.
Immature (probably female) Cassiar Junco, Beaverton, Oregon, 28 March 2011 by Greg Gillson.
The male Cassiar Junco joined a first winter female that had been hanging around for a couple of weeks. Female and first-year Cassiar Juncos are much more difficult to separate from Slate-colored Juncos, so I was glad to spot the adult male.
The scientific name of Cassiar Junco is Junco hyemalis henshawi (=cismontanus of AOU 1957).
Cassiar Juncos breed in the Rocky Mountains of Canada. In winter they regularly are found from southern British Columbia east to Michigan and from there southward from Arizona to Texas. Scattered individuals wander widely in winter outside this main area.
Both Slate-colored and Cassiar Juncos can be found in small numbers throughout the Pacific Northwest in winter. They aren't too unusual at backyard feeders--most feeders will host a couple during the winter. But next time you see a "Slate-colored Junco" I bet you'll be taking a second, closer, look!
* The Great Lumping of 1983: Besides the juncos, other species lumped in 1983 were Myrtle and Audubon's Warblers into Yellow-rumped Warbler; Red-shafted, Yellow-shafted, and Gilded Flicker into Common Flicker, but Gilded Flicker subsequently given back its status as a species and the other two called Northern Flicker; Baltimore and Bullock's Oriole lumped into Northern Oriole, but this decision was later reversed. Finally, Gray-crowned, Black, and Brown-capped Rosy Finches were all lumped into Rosy-Finch, but then this was reversed later, too, but with "Rosy Finch" altered to "Rosy-Finch." ...And I hear rumors of Yellow-rumped Warblers being re-split in the near future. -- We may get most of the pre-1983 species back, but the damage to birders' psyches from that period will never be repaired.