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 learn more about these birds. Because of this, the dark-eyed junco is a fascinating bird for people who love animals and for researchers.

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."

The dark-eyed junco is now placed in the genus Junco. Its scientific name means "winter junco."

Subspecies

There are 14 or 15 subspecies of dark-eyed junco. These subspecies are grouped into several larger groups. Birders are advised to use detailed references when trying to identify subspecies.

Slate-colored group

These subspecies have dark gray heads, breasts, and upperparts. Females are brownish-gray. They breed in the forests from Alaska to Newfoundland and south to the Appalachian Mountains, and they winter in most of the United States.

White-winged group

This subspecies has a medium-gray head, breast, and upperparts with white wing bars. Females are 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 subspecies have blackish-gray heads and breasts with brown backs and wings. This is the most common subspecies group in the West, breeding 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 group, with pinkish 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 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 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 rare bird. It was once thought to be a type of dark-eyed junco. Now, scientists say it is its own special species. This group of birds changed fast because there were only a few of them.

Description

Adult dark-eyed juncos have gray heads, necks, and breasts. They have 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 in length and have a wingspan of 18 to 25 cm. They weigh from 18 to 30 g. Young juncos may look similar to other birds until they grow their adult feathers.

Their songs are trills, somewhat like those of the chipping sparrow. Their calls include tick sounds and high-pitched tinkling _chip_s. Bird lovers often enjoy studying this species.

Distribution and habitat

The dark-eyed junco lives in forests across North America. In the south, it prefers coniferous or mixed forests. Birds in the north travel south for the winter, usually between September and November. They return to breed from March to April. Some stay in the same place all year, while others move to warmer areas during cold weather. In California, some spend winter at lower elevations than where they breed in summer. During winter, they are often seen near towns and visit bird feeders. The 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 look for food on the ground. In winter, they often stay together in groups. These groups can include several types of birds. They eat mostly seeds and insects. Seeds are their main food all year. But when they build their homes, adult juncos eat more insects. Baby juncos need insects to grow.

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

Breeding

These birds usually build their nests on the ground in a small, cup-like shape. The nests are hidden by plants or other things. Sometimes, nests are placed low in 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 shiny and grayish or pale blue-white, with brown, purple, or gray spots. 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 help scientists learn how new species can form quickly. They have many different looks, such as color patterns, which scientists find interesting. One idea is called the postglacial theory. This theory says that when glaciers melted, junco groups moved north into new areas in North America. These new places had different conditions, which may have made the juncos change over time. Because these areas were new and open, even short periods of separation could create 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 changed just because they were isolated, not because they needed to survive better. 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 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 do not 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.