Excerpts from Jim Conrad's
from the September 4, 2005 Newsletter issued from the Sierra Nevada foothills
somewhat east of Placerville, California, USA
At this time of year I seldom see juncos at this elevation. Juncos are those dark-gray-backed, white- bottomed, small, seed-eating birds who during the summer live mostly in Canada and Alaska, but overwinter in the US. My parents called them snowbirds and were sure that snowbirds came only during our uncommon Kentucky snows. Now I know they were present all winter, just that when we had snow the birds' dark upper parts showed up better beneath our birdfeeder pecking at seeds the more sloppy birds knocked out.
Here when I backpack to around 3500 feet juncos start showing up, even in mid summer. They're permanent residents in western North America's mountains, as well as the East's higher Appalachians and New England.
However, the high-elevation juncos I see here are very different from the ones back East. The ones here have dark gray heads and upper chests and white bellies just like the eastern birds but their backs and wings are pale brown. They look like brown birds who have had their heads dipped into dark gray paint. You can see them at http://www.roysephotos.com/DarkEyedJunco2.html.
When I was a kid these brown-backed juncos were regarded as a different species from the eastern birds. The books called the eastern juncos Slate-colored Juncos, and the brown-backed western species Oregon Juncos. There were other juncos, too, such as the White-winged, Gray-headed and Guadalupe Juncos. A map showing the summer distribution of "Oregon Juncos" at http://www.mbr-pwrc.usgs.gov/id/framlst/BBSMap/ra5679.gif.
Now all those different junco types, including our "Oregon Junco," are lumped into one big coast-to-coast taxon known as the Dark-eyed Junco. In areas where the various subspecies' distributions overlap there is just too much interbreeding and intergrading for the different populations to be maintained as distinct species.
By the way, you'd understand the Dark-eyed Junco's name if you saw the bright YELLOW eyes of the Mexican Junco so common in Mexico above about 5000 feet.