Most Northwest birders are familiar with identification of Oregon and Slate-colored Juncos, but what about the Cassiar Junco (Junco hyemalis cismontanus)? It is a poorly understood population, which means that eBirders can help significantly improve our knowledge. How poorly understood? Take a look at the eBird range map for Cassiar Junco across all of North America. It is full of mysteries!
Mystery #1. Even though records are widespread across much of the lower 48, only two of the grids show higher than the 0-2% frequency, the rarest category. They appear to not be common anywhere.
Mystery #2. Look at the same range map, for the summer months only. They essentially disappear! Only three grids appear, one in northern BC and two in southeast Alaska, and all three are in the 0-2% frequency.
Mystery #3. Go to the winter range map. Records are scattered across the lower 48, with few concentrations, even though the literature reports their breeding range as central Yukon south through northern BC and into central Alberta. A very broad winter range for such a narrow breeding range. Then look a little harder at the winter range map. The Pacific Northwest has a lot of the records of this poorly known race, in fact, there is a male at our feeder as I write this note. The only other area that seems to show a concentration is the Colorado front range, where observers spend a lot of time looking at junco flocks.
Northwest eBirders should be on the lookout for Cassiar Junco and reporting them separately from Slate-colored. They are not as easy to find and identify in the midst of an Oregon Junco flock as Slate-colored, since their pattern is similar to Oregon and since the females may be very difficult to distinguish. The drawings in Sibley, labelled as Canadian Rocky Mountain, are quite good. Males have a black hood, shaped liked an Oregon hood, sharply delineated from gray flanks and a gray back. The male at my feeder shows a brownish tinge in the gray back with all gray flanks. In low light, or when viewed head on, Cassiars are not obviously different and not easy to identify, while either sex of Slate-color is generally recognizable with even a quick glance due to the convex hood shape and lack of contrast between hood, flanks and back.
Other than the 235 Washington and 46 Oregon records presently in eBird, there is little known of their status in the Northwest. The state books provide little information. For Washington, Jewett et al (1953) mention one Lewis County specimen from November 1918 and Wahl et al (2005) do not discuss Cassiar specifically. In Oregon, Gabrielson and Jewett (1940) did not record them, and Marshall et al (2003) mention them but do not separate them from Slate-colored.
Regional journals have little information as well, Mlodinow (2006) reported a ratio of 4 Slate-colored to 1 Cassiar from his observations in the northern Puget Trough from 1997-2002. eBirders really can build our knowledge of the winter distribution. So, scan those junco flocks carefully and report junco sightings to eBird by race while you are birding this winter. And as with many poorly understood populations, a bit of caution is in order, particularly since many females may not be identifiable. If you find a Cassiar, congratulate yourself for observing and recording one of the more mysterious populations in North America.
 A record from California is clearly a data entry error.
 Mlodinow, S.G. 2006. Relative frequency of members of the Slate-colored Junco (Junco hyemalis hyemalis) complex in the Northern Puget Trough. Washington Birds 9: 35-38.
Article by Bill Tweit