Dark-eyed junco

The dark-eyed junco is a species of junco, a group of small, grayish New World sparrows. The species is common across much of temperate North America and in summer it ranges far into the Arctic. It is a variable species, much like the related fox sparrow, and its systematics are still not completely resolved.

Taxonomy

The dark-eyed junco was formally described by the Swedish naturalist Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Fringilla hyemalis. The description consisted merely of the laconic remark "F nigra, ventre albo. and a statement that it came from America. Linnaeus based his description on the "Snow-Bird" that Mark Catesby had described and illustrated in his 1731 The Natural History of Carolina, Florida and the Bahama Islands.

The Bill of this Bird is white: The Breast and Belly white. All the rest of the Body dark grey; but in some places black, inclining to Lead-color. In Virginia and Carolina they appear only in Winter: and in Snow they appear most. In Summer none are seen. Whether they retire and breed in the North or where they go, when they leave these Countries in Spring, is to me unknown.

The type locality was restricted to South Carolina by the American Ornithologists' Union in 1931. The dark-eyed junco is now placed in the genus Junco that was introduced in 1831 by the German naturalist Johann Georg Wagler. The genus name Junco is the Spanish word for rush, from the Latin word juncus. Its modern scientific name means "winter junco", from the Latin word "of the winter".

Subspecies

Either 14 or 15 subspecies are recognized. These subspecies are grouped in two or three large or polytypic groups and three or four small or monotypic ones, all depending on the authority. These groups were formerly considered separate species, but they interbreed extensively in areas of contact. Birders trying to identify subspecies are advised to consult detailed identification references.

Slate-colored group

Slate-colored dark-eyed junco - Alaska, across Canada from Newfoundland and Labrador to British Columbia, northeast U.S. from Massachusetts to Minnesota, northwest Mexico from Baja California to Chihuahua, and Gulf Coast states
Carolina dark-eyed junco - Appalachian Mountains from northwest West Virginia and western Maryland south to northern Georgia
Cassiar dark-eyed junco x Oregon dark-eyed junco hybrid - Yukon, British Columbia, and Alberta south through Great Plains down toward north-central Mexico

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

White-winged group

white-winged dark-eyed junco

This subspecies has a medium-gray head, breast, and upperparts with white wing bars. Females are washed brownish. It has more white in the tail than the other 14 subspecies. It is a common endemic breeder in the Black Hills of South Dakota, Wyoming, Nebraska, and Montana, and winters south to northeastern New Mexico.

Oregon or brown-backed group

Montana dark-eyed junco - Interior British Columbia, Alberta, eastern Washington, northeast Oregon, Idaho, Montana, & Wyoming
Nevada dark-eyed junco - Great Basin
Oregon dark-eyed junco - Coastal southeast Alaska to central British Columbia
Point Pinos dark-eyed junco - Coastal California
Laguna Hanson dark-eyed junco - Mountains of northern Baja California
Shufeldt's dark-eyed junco - West slopes of coastal mountains from western Oregon to southwest British Columbia
Thurber's dark-eyed junco - Interior California
Townsend's dark-eyed junco - Mountains of northern Baja California

These eight subspecies have blackish-gray heads and breasts with brown backs and wings and reddish flanks, tending toward duller and paler plumage in the inland and southern parts of its range. Oregon dark-eyed juncos are also less commonly 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 extreme northern Baja California and wintering to the Great Plains and northern Sonora. An unresolved debate exists as to whether this large and distinct subspecies group is actually a separate species with eight subspecies of its own.

Pink-sided group

pink-sided dark-eyed junco

Sometimes considered a ninth subspecies in the Oregon/brown-backed group, this subspecies has a lighter gray head and breast than the eight Oregon/brown-backed dark-eyed juncos, with contrasting dark lores. The back and wings are brown. It has a pinkish-cinnamon color that is richer and covers more of the flanks and breast than in the eight Oregon/brown-backed dark-eyed juncos. It breeds in the northern Rocky Mountains from southern Alberta to eastern Idaho and western Wyoming and winters in central Idaho and nearby Montana and from southwestern South Dakota, southern Wyoming, and northern Utah to northern Sonora and Chihuahua.

Gray-headed group

gray-headed dark-eyed junco

This subspecies is essentially 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

red-backed dark-eyed junco

Sometimes included with the gray-headed dark-eyed junco proper as part of the gray-headed group, this subspecies differs from it in having a more silvery bill with a dark-colored upper mandible and a light-colored lower mandible, a variable amount of rust on the wings, and pale underparts. This makes it similar to the yellow-eyed junco, except for the dark eyes. It is found in the southern mountains of Arizona and New Mexico. It does not overlap with the yellow-eyed junco in its breeding range.

Related species

The extremely rare Guadalupe junco was formerly considered to be a subspecies of this species, but is now treated as a separate species in its own right – perhaps a rather young one, but certainly this population has evolved more rapidly than the 14 or 15 subspecies of the dark-eyed junco on the mainland due to its small population size and the founder effect.

Description

Adult dark-eyed juncos generally have gray heads, necks, and breasts, gray or brown backs and wings, and a white belly, but show a confusing amount of variation in plumage details. The white outer tail feathers flash distinctively in flight and while hopping on the ground. The bill is usually pale pinkish.
Males tend to have darker, more conspicuous markings than females. The dark-eyed junco is long and has a wingspan of. Body mass can vary from. Among standard measurements, the wing chord is, the tail is, the bill is and the tarsus is. Juveniles often have pale streaks on their underparts and may even be mistaken for vesper sparrows until they acquire adult plumage at two to three months, but dark-eyed junco fledglings' heads are generally quite uniform in color already, and initially their bills still have conspicuous yellowish edges to the gape, remains of the fleshy wattles that guide the parents when they feed the nestlings.
The song is a trill similar to the chipping sparrow's, except that the red-backed dark-eyed junco's song is more complex, similar to that of the yellow-eyed junco. The call also resembles that of the black-throated blue warbler which is a member of the New World warbler family. Calls include tick sounds and very high-pitched tinkling chips. It is known among bird song practitioners as an excellent bird to study for learning "bird language".

Distribution and habitat

The dark-eyed junco's breeding habitat is coniferous or mixed forest areas throughout North America. In otherwise optimal conditions it also utilizes other habitats, but at the southern margin of its range it can only persist in its favorite habitat. Northern birds migrate further south, arriving in their winter quarters between mid-September and November and leaving to breed from mid-March onwards, with almost all of them gone by the end of April or so. Many populations are permanent residents or altitudinal migrants, while in cold years they may choose to stay in their winter range and breed there. For example, in the Sierra Nevada Mountains of eastern California, J. hyemalis populations will migrate to winter ranges lower than their summer range. Seasonally sympatric females show difference in migration and reproductive timing that is dependent on hormone and ovary regulation. The migrant female J. hyemails experience delayed growth in the gonad to allow time for their seasonal migration. They then migrate down to the northeastern United States, where the resident subspecies is the Carolina dark-eyed junco. Female Carolina dark-eyed juncos have large ovaries and, therefore, do not experience gonadal growth delays because they are residents in the area. In winter, dark-eyed juncos are familiar in and around towns, and in many places are the most common birds at feeders. The slate-colored dark-eyed junco is a rare vagrant to Western Europe and may successfully winter in Great Britain, usually in domestic gardens.

Behavior and ecology

These birds forage on the ground. In winter, they often forage in flocks that may contain several different subspecies. They mainly eat seeds and insects, with seeds comprising three quarters of their year-round diet. However, during the breeding season, insects comprise nearly half of the diet of adult dark-eyed juncos. Young dark-eyed juncos also depend on a diet of mainly insects.
A flock of dark-eyed juncos has been known to be called a blizzard.