In the Eyes of Juncos

We found some early migrant Dark-eyed Juncos grazing like pretty little cows on the lawn at Fort Rosecrans National Cemetery in San Diego. The birds were fairly bold, approaching to within 10 feet of us, probably because there was a bit of a stiff breeze blowing, and they were sheltering in the lee of a low cement wall. To give you an idea how close these normally shy little birds were, these photos were taken with a Canon 40D DSLR equipped with a 75-300 mm zoom lens. We took the photos, in part, because there was an interesting juxtaposition here: one is a male Oregon Junco and the other is a male Pink-sided Junco.

Oregon Junco

Oregon Junco

Let’s back up a bit. For starters, Dark-eyed Junco is actually a complex of six different ‘recognizable forms’ or sub-species: Slate-colored, Oregon, Pink-sided, Gray-headed, Red-backed and White-winged. For our purposes here, it’s worth noting that the latter two sub-species are seldom seen in Southern California, but the first four are all encountered quite regularly. Of those, the Oregon form is the most common, and it comprises by far the largest portion of our juncos. Adult Dark-eyed Junco males like our bird have a very dark gray or even dull black hood, a brownish back, pale pinkish or rust-colored flanks and a whitish belly, topped off by a lovely little sharp pink bill. Ironically, the dark eye, for which the species complex is named, is barely visible in Oregon Juncos since it is essentially the same color as the hood. A good look at our pictured bird shows that it fits this description pretty well.

Pink-sided Junco

Pink-sided Junco

Contrast that with the other bird. This bird has the same pink bill, but the hood is a light bluish gray. This creates a visible contrast with the blackish area between the bill and the eye (the lore). The back is a pale, dull brown, and a slight wash of the same color is visible in the nape. This bird also shows light pinkish flanks and a paler belly region. In fact, separation of an adult male Oregon from an adult male Pink-sided Junco is not difficult. The potential point of confusion is actually with either a female Oregon form, or a Gray-headed Junco. The most useful characters for distinguishing Pink-sided Junco from female Oregon Juncos is that the hood on the Oregon is always darker, and never shows the black lores. The Gray-headed Junco does show black lores, but it has a distinctly reddish back that is much brighter than the dull brown back of a Pink-sided Junco.

How much does all this matter? The junco forms were originally thought to be full species, distinct from one another, but genetic analysis revealed that their mitochondrial DNA was so similar that they could not be called full species. The juncos themselves don’t seem to care all that much. Where their ranges overlap, they are known to interbreed. For whatever reasons, when these sub-species interbreed, the result is always one of the color forms or phenotypes; interbreeding doesn’t produce visible intergrades. So in the eyes of juncos, it’s all the same, which means that junco forms are just one of those games birders play.

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