Dark-eyed juncos are one of our most common and abundant birds. They flock to backyard feeders all over North America in nearly a dozen distinctive color variations.
Juncos earned the nickname “snowbirds” because that’s when they are most often seen. But in the Pacific Northwest, our Oregon subspecies is a year-round resident. Its slate-colored head, brown mantle and flashing white tail fringes are easy to spot as they boldly feed on and under our sunflower and millet feeders. These adaptable sparrow-sized birds can nest almost anywhere — on the ground or in bushes, planter boxes and flower pots.
Dark-eyed juncos are found only in North America. The Mexican species are more closely related to the yellow-eyed junco, a near relative of the dark-eyed junco.
Ornithologists have long puzzled over the fact that the various junco subspecies freely interbreed wherever ranges overlap. You would think their color patterns would become more blended in time. But regional patterns remain strikingly different.
Dr. Jonathan Atwell, a research scientist at Indiana University, wrote an extensive profile on the dark-eyed junco, featured in the January/February 2018 issue of Bird Watcher’s Digest. In it, he describes 1930s research by pioneering ornithologist Alden Miller. Using the traditional shotgun method, Alden collected an astounding 11,774 specimens and sorted them into 15 categories based on differences in appearance.
The American Ornithological Union (now the American Ornithological Society) has waffled on classification, changing the dark-eyed junco five times between 1886 and 1998. First, there were five species, then seven, then three, then six, then five; and in 1983 they settled on a single species.
Dr. Borja Mila, a research scientist with Spain’s National Museum of Natural Sciences, sequenced 142 DNA samples representing 23 different U.S. junco populations. The results, published in 2013, were so similar, he concluded that any differences were comparatively recent, and have occurred almost entirely within the last 10,000 years as juncos expanded their breeding ranges northward from Mexico into the forests of the U.S. and Canada following the retreat of the most recent Ice Age.
So, despite their striking differences in color, dark-eyed juncos share a relatively recent common ancestor (10,000 years is a blink of an eye in geologic time).
— Gene Bullock is a member of the Kitsap Audubon Society and writes a monthly birding column for Kitsap Weekly. You can reach him at firstname.lastname@example.org.