The Dark-eyed Junco (Junco hyemalis) is a species of the juncos, a genus of small grayish American sparrows. This bird is common across much of temperate North America and in summer ranges far into the Arctic. It is a very variable species, much like the related fox sparrow (Passerella iliaca), and its systematics are still not completely untangled.
Adults 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.
The several subspecies make up two large groups and three to five small or monotypic ones. The five basic groups were formerly considered separate species (and the Guadalupe junco frequently still is), but they interbreed extensively in areas of contact. Birders trying to identify subspecies are advised to consult detailed identification references.
White-winged junco 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 forms. It is a common endemic breeder in the Black Hills area of South Dakota, Wyoming, Nebraska, and Montana, and winters south to northeastern New Mexico.
Oregon junco J. h. montanus, J. h. oreganus, J. h. pinosus, J. h. pontilis, J. h. shufeldti, J. h. thurberi, J. h. townsendi These have a blackish-gray head and breast with a brown back and wings and reddish flanks, tending toward duller and paler plumage in the inland and southern parts of its range. This is the most common form in the west, found in the Pacific coast mountains from southeastern Alaska to extreme northern Baja California, wintering to the Great Plains and northern Sonora. An unresolved debate exists as to whether this large and distinct group is a full species[citation needed].
Pink-sided junco J. h. mearnsi Often considered part of the Oregon group, it has a lighter gray head and breast than the Oregon group with contrasting dark lores. The back and wings are brown. It has pinkish-cinnamon color that is richer and covers more of the flanks and breast than in Oregon juncos. It breeds in the northern Rocky Mountains from southern Alberta to eastern Idaho and western Wyoming; it winters in central Idaho and nearby Montana and from southwestern South Dakota, southern Wyoming, and northern Utah to northern Sonora and Chihuahua.
Gray-headed junco J. h. caniceps 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 junco J. h. dorsalis Often included with J. h. caniceps as 'gray-headed juncos, it differs from the gray-headed junco proper in having a more silvery bill[ with a dark upper mandible, a variable amount of rust on the wings, and pale underparts. This makes it similar to the yellow-eyed junco (J. phaeonotus) except for the dark eye. It is found in the southern mountains of Arizona and New Mexico. It does not overlap with the yellow-eyed junco in breeding range.
Guadalupe junco J. h. insularis The extremely rare Guadalupe junco is also considered part of this species by some authors, namely the IUCN, which restores it to subspecies status in 2008.[12][13] Other authors consider it a species in its own right – perhaps a rather young one, but certainly this population has evolved more rapidly than the mainland juncos due to its small population size and the founder effect.