Dark-eyed Junco

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 13 to 17.5 cm (5.1 to 6.9 in) long and has a wingspan of 18 to 25 cm (7.1 to 9.8 in). Body mass can vary from 18 to 30 g (0.63 to 1.06 oz). Among standard measurements, the wing chord is 6.6 to 9.3 cm (2.6 to 3.7 in), the tail is 6.1 to 7.3 cm (2.4 to 2.9 in), the bill is 0.9 to 1.3 cm (0.35 to 0.51 in) and the tarsus is 1.9 to 2.3 cm (0.75 to 0.91 in). Juveniles often have pale streaks on their underparts and may even be mistaken for vesper sparrows (Pooecetes gramineus) 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 (Spizella passerina), except that the red-backed dark-eyed junco's (see above) song is more complex, similar to that of the yellow-eyed junco (Junco phaeonotus). …

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 5,000–7,000 feet (1,500–2,100 m) 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 (J. h. carolinensis). Female Carolina dark-eyed juncos have large ovaries and, therefore, do not experience gonadal growth delays because they are residents in the area. …

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.

Breeding. Dark-eyed juncos usually nest in a cup-shaped depression on the ground, well-hidden by vegetation or other material, although nests are sometimes found in the lower branches of a shrub or tree. The nests have an outer diameter of about 10 cm (3.9 in) and are lined with fine grasses and hair. Normally, two clutches of four eggs are laid during the breeding season. The slightly glossy eggs are grayish or pale bluish-white and heavily spotted (sometimes splotched) with various shades of brown, purple or gray. The spotting is concentrated at the large end of the egg. The eggs are incubated by the female for 12 to 13 days. The young leave the nest between 11 and 14 days after hatching.