Each summer, flocks of Dark-eyed Juncos make their way to northern reaches of Canada in search of a mate. Then, as temperatures drop, they head south, populating the entire continental United States (minus the southern tip of Florida) until the snow melts. Early ornithologists nicknamed them the “snow bird” due to their frequent appearance during winter and total absence in spring and summer.
Many of our readers likely know that “junco” is Spanish for “rush,” from the Latin juncus. Its scientific name is Junco hyemalis, literally “rush of the winter.”
The Junco template is simple—they come in uniform size, about five inches from tail feather to beak, a gray body, white underside, and a stubby, pink beak. But within this template exists over a dozen subspecies. So many subspecies, in fact, that scientists use juncos as a model for what’s called “rapid speciation.”
Speciation refers to an evolutionary process wherein a population within a species develops unique characteristics that set it apart from the greater population. Scientists theorize that Dark-eyed Juncos branched off from Yellow-eyed Juncos about 1,800 years ago in response to melting glaciers and more territory becoming habitable across North America. From there, genetic drift and selection lead to further speciation among Juncos. Genetic drift is the fluctuation of a particular gene in a population due to chance, and selection just means the process by which a mate is chosen, with better adapted and flashier males prevailing over their drab counterparts.
Most of the differences between Juncos have no bearing on how well adapted they are to their environment and have more to do with small populations being cut off from one another and breeding within those habitats. Thus, we have these variations: red-backed juncos, pink-sided juncos (the common subspecies in northern New Mexico), gray-headed juncos and white-winged juncos. Telling these subspecies apart is very difficult and can stump even professional birders. Further complicating matters is the fact Juncos carry no animosity for other subspecies and will frequently interbreed, creating even more new combinations.
Juncos prefer coniferous forests, but you won’t spot them up in the branches. No, this is a bird that likes to lay low, hopping about the pine-needle-strewn ground for seeds and insects. Even their nests are built into the ground, typically a small cup-shaped indentation in the earth covered by loose vegetation or whatever the homemaker can scrounge together.
You can attract them to your yard with a seed feeder, and don’t worry about buying the fancy seeds, these guys will eat anything. If you have messy eaters that knock seeds all over the ground, Juncos will be your cleanup crew, dutifully chirping away as they feast on the leftovers.
These tiny birds are nothing if not resilient, braving freezing temperatures and proving remarkably adaptable. While other species flee urbanized areas, Juncos have been studied for their ability to live within urbanized areas. This was first documented in a population of them at the University of California-San Diego. While other Juncos migrated, the campus population remained year-round. Because of this they yielded four broods each year instead of the standard two, leading to increased competition and selection. Upon studying the genes of these Juncos, scientists found they had, in a span of mere decades, developed a gene that provided high tolerance to the heavy metals found in urban areas. The research on Juncos is scant but further study promises to illuminate the mysteries of how birds adapt to urban environments.
The good news is because of their ability to adapt, these little guys aren’t going anywhere anytime soon. Their population is estimated to be around 630 million, almost twice the human population of the United States. Scatter some seed around your yard and enjoy these winter visitors before they fly back to Canada next spring.
