Dark-eyed junco

The dark-eyed junco (Junco hyemalis) is a type of small bird called a junco. Juncos are small, grayish birds that belong to the group of New World sparrows. These birds are often seen in fields, forests, and backyards across much of temperate North America. In the summer, they can even be found far up into the Arctic.

This species is interesting because it looks different in various places, much like the fox sparrow (Passerella iliaca). Scientists are still studying them to fully understand how they are related to other birds. Because of this, the dark-eyed junco remains a fascinating subject for bird lovers and researchers alike.

Taxonomy

The dark-eyed junco was first described by the Swedish naturalist Carl Linnaeus in 1758. He called it Fringilla hyemalis, meaning "a black finch with white belly." Linnaeus based his description on a bird called the "Snow-Bird" described by Mark Catesby.

The dark-eyed junco is now placed in the genus Junco, a name that comes from the Spanish word for rush. Its scientific name means "winter junco."

Subspecies

There are either 14 or 15 subspecies of dark-eyed junco. These subspecies are grouped into several larger groups. These groups were once thought to be separate species, but they interbreed where their ranges overlap. Birders are advised to use detailed references when trying to identify subspecies.

Slate-colored group

These subspecies have dark slate-gray heads, breasts, and upperparts. Females are brownish-gray, sometimes with reddish-brown flanks. They breed in the boreal forests from Alaska to Newfoundland and south to the Appalachian Mountains, wintering throughout most of the United States.

White-winged group

This subspecies has a medium-gray head, breast, and upperparts with white wing bars. Females are washed brownish. It breeds in the Black Hills of South Dakota, Wyoming, Nebraska, and Montana, and winters south to northeastern New Mexico.

Oregon or brown-backed group

These eight subspecies have blackish-gray heads and breasts with brown backs and wings and reddish flanks. Oregon dark-eyed juncos are also known as brown-backed dark-eyed juncos. This is the most common subspecies group in the West, breeding in the Pacific Coast Ranges from southeastern Alaska to northern Baja California and wintering to the Great Plains and northern Sonora.

Pink-sided group

This subspecies has a lighter gray head and breast than the Oregon/brown-backed dark-eyed juncos, with a pinkish-cinnamon color on the flanks and breast. It breeds in the northern Rocky Mountains from southern Alberta to eastern Idaho and western Wyoming and winters in central Idaho, Montana, and parts of the western United States.

Gray-headed group

This subspecies is rather light gray on top with a rusty back. It breeds in the southern Rocky Mountains from Colorado to central Arizona and New Mexico, and winters into northern Mexico.

Red-backed group

This subspecies has a more silvery bill and variable rust on the wings. It is found in the southern mountains of Arizona and New Mexico.

Related species

The Guadalupe junco (Junco insularis) is a very rare bird that was once thought to be a type of dark-eyed junco. Now, scientists consider it a separate species. This small group of birds changed quickly because there were only a few of them and they came from a very small original group.

Description

Adult dark-eyed juncos have gray heads, necks, and breasts, along with gray or brown backs and wings. They have a white belly, and their white outer tail feathers stand out when they fly or hop. Their bills are usually a pale pinkish color.

Males often have darker markings than females. These birds measure between 13 to 17.5 cm (5.1 to 6.9 in) in length and have a wingspan of 18 to 25 cm (7.1 to 9.8 in). They weigh from 18 to 30 g (0.63 to 1.06 oz). Young juncos may look similar to other birds until they grow their adult feathers, but even as fledglings, their heads are usually a uniform color.

Their songs are trills, somewhat like those of the chipping sparrow, but the red-backed dark-eyed junco has a more complex song. Their calls include tick sounds and high-pitched tinkling _chip_s. Bird lovers often enjoy studying this species to learn more about bird sounds.

Distribution and habitat

The dark-eyed junco lives in coniferous or mixed forests across North America. In some areas, it can also be found in other types of habitats, but in the southern parts of its range, it mainly stays in its favorite forest homes. Birds that live in the northern areas travel further south for the winter, usually arriving between mid-September and November. They leave again to breed from mid-March, with most gone by the end of April. Some groups stay in the same place all year, while others move to lower areas during cold weather. For example, in the Sierra Nevada Mountains of eastern California, some junco populations spend winter at elevations 5,000–7,000 feet lower than where they breed in summer. During winter, dark-eyed juncos are often seen near towns and are common visitors to bird feeders. The slate-colored dark-eyed junco is a rare visitor to Western Europe and might sometimes spend the winter in Great Britain, usually in gardens.

Behavior and ecology

Dark-eyed juncos search for food on the ground. In winter, they often stay together in groups that can include several different types of these birds. They eat mostly seeds and insects, with seeds making up most of their diet all year. But during the time when they make their homes, adult juncos eat almost half insects, and baby juncos need mostly insects to grow.

A group of dark-eyed juncos is sometimes called a blizzard.

Breeding

These birds usually build their nests in a small, cup-like shape on the ground, hidden by plants or other things. Sometimes, nests are placed in the lower parts of bushes or trees. The nests are about 10 cm (3.9 in) wide and lined with soft grasses and hair. Typically, a female lays two groups of four eggs each breeding season. The eggs are a bit shiny and grayish or pale blue-white, with brown, purple, or gray spots, mostly at the larger end. The female sits on the eggs for about 12 to 13 days until they hatch. The baby birds leave the nest in about 11 to 14 days after hatching.

Diet

Dark-eyed juncos eat mostly insects and seeds, along with berries.

Evolution

Postglacial theory and diversification

Dark-eyed juncos are often studied to understand how new species can develop quickly. They show a lot of variety in their looks, like different color patterns, which scientists find interesting. One idea about why they changed so much is called the postglacial theory. This theory suggests that when glaciers melted, junco populations moved north into new areas in North America. These new places had different conditions, which may have caused the juncos to change over time. Because these areas were new and open, even short periods of separation could lead to big differences between groups.

The Oregon junco group also changed in interesting ways. Some groups lived in places far apart, like deserts, which kept them separated. These groups didn’t need to be better at surviving to change—they just changed because they were isolated. Other groups lived closer together and mixed more, but still looked different because they adapted to their specific environments, like temperature changes or height above sea level. Scientists think many forces, like natural selection and isolation, worked together to make these juncos diversify so quickly.

Urbanization

Dark-eyed juncos in urban areas, like on the University of California, San Diego campus, show how birds can adapt to city life. These juncos don’t migrate like others; they stay year-round because San Diego has mild weather. This allows them to have more breeding seasons and larger families. Because they breed more often, fathers may help more with raising the young.

Studies show these urban juncos are quite different from nearby groups, almost as if they lived far away. Originally thought to come from a local group, tests show they likely came from a coastal group 20–30 generations ago. This small founding group and their new environment helped them change quickly. Some genes in these birds help them survive in cities, like tolerating heavy metals or making higher-pitched calls that can be heard over city noise.

Research also found that urban juncos face fewer certain parasites compared to those in rural areas, which might also affect how they adapt. A study during the COVID-19 pandemic showed that bill shapes in juncos at UCLA changed during lockdowns and returned to previous shapes afterward, suggesting diet changes impact their development.