The Dark-eyed Junco is currently divided into six distinct populations that include the following: Oregon, Pink-sided, White-winged, Slate-colored, Gray-headed, and Red-backed Juncos. There are an additional 12 subspecies divided among these populations.
The Gray-headed Junco is the only population that breeds in Colorado. All the populations except the Red-backed are found in Colorado in the winter.
The Dark-eyed Junco has been documented to produce hybrids with White-throated Sparrows.
Dark-eyed Juncos are often called “Snowbirds,” possibly due to the fact that many people believe their return from their northern breeding grounds foretells the return of cold and snowy weather. Another possible source of the nickname may be the white belly plumage and slate-colored back of the junco which has been described as “leaden skies above, snow below.”
Juncos spend the entire winter in flocks averaging in size from six to thirty or more birds.
Dark-eyed Juncos tend to return to the same area each winter. Chances are that you have many of the same birds at your feeder this winter that you had in previous years.
Visiting flocks of juncos will usually stay within an area of about 10 acres during their entire winter stay.
To avoid the competition, many female juncos migrate earlier and go farther south than most of the males. In Michigan only 20% of the wintering juncos are females, whereas in Alabama 72% were found to be female.
Male juncos tend to spend the winter farther north in order to shorten their spring migration and thus gain the advantage of arriving first at prime breeding territories.
When migrating, female juncos move south before the males do, and adult females leave before the young females.
Juncos migrate at night at very low altitudes and are susceptible to collisions with communication towers and other structures.
Each winter flock of juncos has a dominance hierarchy with adult males at the top, then juvenile males, adult females and young females at the bottom. You can often observe individuals challenging the status of others with aggressive displays of lunges and tail flicking.
While almost all Slate-colored Juncos in the Eastern portion of North America migrate, a population of juncos in the Appalachian Mountains is residential, remaining in the same area year-round.
While the southward migration of Slate-colored Juncos is complete by early December, there is some evidence that indicates that harsh winter weather may spur some Juncos to move further south at anytime during the winter.
Juncos have over 30 percent more feathers (by weight) in the winter than they do in summer.
Juncos prefer to roost in evergreens at night but will also use tall grasses and brush piles. They return to the same roost location repeatedly and will share it with other flock mates, but they do not huddle together.
The name junco is derived from the Latin word for the “rush” plant found in wetlands.
Partners in Flight currently estimates the North American population of Dark-eyed Juncos at approximately 260 million, second only to the American Robin in overall population size in North America. A separate research paper estimates that the junco population could actually be as high as 630 million.
According to Project Feeder Watch, juncos are sighted at more feeding areas across North America than any other bird. Over 80% percent of those responding report juncos at their feeders.
A study in New Hampshire on the foraging habitats of the Slate-colored Juncos found that they spent over 65% their time on the ground, 20% in shrubs, 16% in saplings or low trees. They were never observed in the canopy of large trees.
Juncos, along with some other members of the sparrow family, practice an interesting foraging method called “riding.” They fly up to a seed cluster on the top of a grass stem and “ride” it to the ground where they pick off the seeds while standing on it.
Juncos are known to burrow through snow in search of seeds that have been covered over.
On an annual basis, a junco’s diet is made up of approximately three parts seeds to one part insects. During the nesting period, the percent of insects can increase up to 50 or 60 % of their diet.
You may not like these weeds in your yard, but the seeds of chickweed, ragweed, knotweed, pigweed, lamb’s quarters and crabgrass are some of the main natural seed sources used by juncos.
You can attract juncos to your yard by feeding a seed blend containing millet and hulled sunflower seeds.
Male juncos return and reclaim the same breeding territory year after year.
Juncos typically have two broods per year with the female building her nest on or near the ground and laying 3-5 eggs. The male does not incubate the eggs but does deliver food to the young and helps the female to defend against predators. The young leave the nest in 9-12 days.
Studies have shown that Dark-eyed Junco’s nests are the victim of predators between 20 and 80% of the time. Rodents such as chipmunks and deer mice are probably the major predators on the eggs of juncos.