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Junco hyemalisdark-eyed junco

By Aynsley Carroll

Geographic Range

Dark-eyed juncos (Junco hyemalis) breed from Alaska and central Yukon to Labrador and Newfoundland, south to central coastal California, in the mountains to eastern California, central Arizona, and western Texas, southern Alberta, northern and east-central Minnesota, central Michigan, southern New England, and in the Appalachian Mountains to northern Georgia and northwestern South Carolina; also in the Black Hills. This species winters from central and south coastal Alaska, coastal British Columbia and across southern Canada south to Mexico, the Gulf Coast and northern Florida. It is found only in the Nearctic region of the world. (United States Department of Agriculture, 1991)

Habitat

The habitat of J. hyemalis occurs from sea level to timberline in a variety of woodland areas that have openings with dense herbaceous ground cover. These areas include coniferous and deciduous forests, forest edges, woodland clearings, stream borders, open woodlands, brushy cover bordering mountain meadows, and old barns. This species avoids deep forest interiors in favor of woodland edges and openings. In winter they prefer weedy fields, but also inhabit open woodlands, hedgerows, suburbs, and farmyards. They are found from sea level to 3500 meters. (Nolan, et al., 2002; United States Department of Agriculture, 1991)

  • Range elevation
    0 to 3500 m
    0.00 to 11482.94 ft

Physical Description

All J. hyemalis are small and slender with an overall length of 5 to 6.5 inches (12.5 to 16.5 cm). This species has dark gray plumage on its head, breast and upper parts which are a contrast to their striking white, outer tail and white belly. Sexes are colored or patterned differently with female and immature J. hyemalis somewhat browner than the adult male; juveniles also have streaked breasts. Males are usually around 5% larger than females. Members of this species have a pink bill and dark eyes. A typical weight for J. hyemalis is 0.67 oz (19 g) and an average wingspan is 9.25 inches (23.5 cm). (Barrowclough, 1983; Reader's Digest Association, 1991; Sibley, 2000; Sullivan, 1999)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • Average mass
    19 g
    0.67 oz
  • Average mass
    18 g
    0.63 oz
    AnAge
  • Range length
    12.5 to 16.5 cm
    4.92 to 6.50 in
  • Average wingspan
    23.5 cm
    9.25 in
  • Average basal metabolic rate
    46 cm3.O2/g/hr
  • Average basal metabolic rate
    0.2959 W
    AnAge

Reproduction

Dark-eyed juncos are monogamous. Males usually arrive on breeding grounds in the spring, well in advance of the start of nesting, and pairs are formed by mid-April. Males claim territories by singing from the top of the tallest trees in a 2 to 3 acre area. When a female enters his territory, the male pursues her aggressively. He spreads his tail and struts around the female, uttering "chips" and songs. The male may alternate dropping his tail to the ground with lifting it at a 45 degree angle. Once a pair is formed, males follow their mates and are seldom more than 50 feet away. The only exception is when the male proclaims his occupancy of a territory from a high perch. (Bent and et al, 1968; Kennedy, 2002; Nolan, et al., 2002; Sullivan, 1999)

The breeding season for dark-eyed juncos begins in April. Females build the nest over a period of 1 to 9 days, but the male often helps by bringing nest material. Nests are commonly built on the ground near the edge of openings in wooded areas or in a slight depression. They are usually well concealed under weeds, grasses, fallen logs, tree roots, or other overhead shelter. Nests are occasionally built up to 8 feet above ground in a shrub or tree. The nest cup is often lined with fine grasses, mosses or mammal hair and is used for two or three broods in one season.

The female lays 3 to 6 white or pale green eggs spotted with brown. The eggs are usually ovate and slightly glossy. Average egg size is about 0.8 inches (19 mm). The incubation period lasts 12 to 13 days; incubation is usually done by the females. Chicks leave the nest 9 to 13 days after hatching. After leaving the nest, the young remain at least partially dependent on their parents for about 3 weeks. Most dark-eyed juncos begin breeding at at 1 year. (Bent and et al, 1968; Brewer, et al., 1991; Nolan, et al., 2002; Reader's Digest Association, 1991; Sullivan, 1999; United States Department of Agriculture, 1991)

  • Breeding interval
    May breed 2 to 3 times during the spring and early summer each year
  • Breeding season
    Dark-eyed juncos begin breeding in April
  • Range eggs per season
    3 to 6
  • Average eggs per season
    4
  • Average eggs per season
    4
    AnAge
  • Average time to hatching
    12 to 13 days
  • Average time to hatching
    11 days
    AnAge
  • Range fledging age
    9 to 13 days
  • Range time to independence
    9 to 21 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

The female parent incubates the eggs and broods the chicks after they hatch. Both parents defend the nest from predators, remove fecal sacs from the nest and feed the chicks regurgitated or partly digested food along with an occasional tender caterpillar. Chicks are altricial and begin to open their eggs at the end of the second day. Their feathers begin to show around the seventh day. Rapid tarsal development enables nestlings to run from the nest if threatened before they can fly. Youngsters leave the nest 9 to 13 days after hatching. After leaving the nest, the young remain at least partially dependent on their parents for food for about 3 weeks. Occasionally, young will attempt to solicit parental care and crouch in a begging posture even after they are adequately developed for independence. Parents become aggressive in these cases and chase the fledgling a short distance without feeding it. (Bent and et al, 1968; Kennedy, 2002; Reader's Digest Association, 1991)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

The average lifespan of J. hyemalis is approximately 3 to 11 years. The oldest known wild dark-eyed junco lived at least 11 years 1 month. Most commonly, predation by other species (hawks, squirrels, weasels, etc.) limits their lifespan. (Nolan, et al., 2002; The Norman Bird Sanctuary, 2000)

  • Range lifespan
    Status: wild
    11.1 (high) years
  • Typical lifespan
    Status: wild
    3 to 11 years

Behavior

Dark-eyed juncos usually hop or walk as they move along the ground and can travel up to 30 cm in one hop. Exceptions are running in short spurts when chasing a rival or to capture moving food. This species is social during autumn and winter months and consorts in flocks. Winter flocks tend to be small, typically 15 to 25 individuals. Flocks form in the morning, 20 to 30 minutes before sunrise and disperse in the evening, 45 minutes before sunset to roost for the night. Daylight hours are spent either perching or foraging for food and allocation of time between these two activities varies with season and the stage of reproductive cycles. On average, individuals forage for 4.5 hours a day in the summer and 6 hours a day in the winter to meet higher energy demands. It is not uncommon for these flocks to associate with those of American tree sparrows (Spizella arborea).

Dark-eyed juncos tend to winter in the same area year after year. The flock stays in an area roughly 10 to 12 acres in size, but not all members of the flock are together all of the time. There is a social hierarchy within the winter flocks. Males tend to be dominant over females and adults are dominant over the younger birds. Because males are dominant over females in winter flocks, females have less access to food. Therefore, they do not fair well in flocks composed of many males. Females tend to winter farther south away from the males. Males need to risk harsh winters farther north in order to be closer to their breeding grounds. Females do not need to compete for territories in the spring and can take their time returning. Older males almost always return to their old, established territories. The younger males winter the farthest north and must work hard to claim a breeding spot. Dominant birds have an advantage when feeding and claiming territories and will face another bird and raise and fan their tails, revealing the white outer tail feathers. They may also rush at or peck at subordinate birds in order to chase them away. Aggressive behavior occurs mainly in winter flocks and increases with increasing flock size.

Most dark-eyed junco populations are migratory. However, some populations, particularly several montane subspecies, are sedentary or partially migratory. (Bent and et al, 1968; McPeek, 1994; Sibley, 2000; Stokes Nature Company, 2002; Sullivan, 1999)

  • Range territory size
    10,000 to 20,000 m^2

Home Range

Winter flocks have a home range of 10 to 12 acres. (Sullivan, 1999; United States Department of Agriculture, 2002)

Communication and Perception

Dark-eyed juncos (Junco hyemalis) possess considerable variation in song. The most common song is a simple, musical trill, all in one pitch, or a series of rapid notes which may be too rapid to discern. Only male dark-eyed juncos sing. To proclaim occupancy of a territory, two or three trills on different pitches may be joined to form a single warbling song. A simple explosive call is used as an alarm, while a smacking sequence is used to scold. This species uses a combination of twanging, buzzing, and smacking notes when fighting.

Junco hyemalis also uses territorial and courtship displays to communicate (see Mating Systems and Behavior). (Bent and et al, 1968; Sullivan, 1999)

Food Habits

Dark-eyed juncos forage on the ground, picking up a wide variety of seeds and some insects. In the non-breeding season, they prefer to feed on insects, non-insect arthropods, and seeds. During the breeding season, they eat mostly insects. They are commonly seen at bird feeders during migration and in the winter months, however, even then they prefer to feed on the ground rather than pick seeds from an elevated feeder. One method of foraging practiced by this species is "riding" a grass stem. This is accomplished by flying up onto a tall grass stem, riding the stem down to the ground as it bends under the bird's weight, and then plucking the seeds from the seed head as it sits on the ground. When a thin layer of snow lies on the ground, dark-eyed juncos scratch away a roughly circular hole, 3 or 4 inches in diameter, to get at the grain underneath. In the summer, half of the diet consists of insects. Caterpillars, beetles, and ants are the most common items in their diet. There is also a long list of mostly weed plants whose seeds J. hyemalis is known to eat. The most common are ragweed, bristlegrass, dropseed grass, crabgrass, pigweed, and goosefoot. Juncos are morphologically generalized enough to handle both seeds and insects as part of their diet. (Bent and et al, 1968; Dunning, 2001; McPeek, 1994; Sullivan, 1999; United States Department of Agriculture, 1991)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • seeds, grains, and nuts

Predation

Because it inhabits open areas, Junco hyemalis is subject to attack by many different birds, including sharp-shinned hawks, shrikes and owls. They are also frequently killed by feral and domestic cats. Red squirrels (Tamiasciurus hudsonicus), weasels (genus Mustela), chipmunks (genus Tamias), American martens (Martes americana) and other mammals as small as jumping mice take eggs and young from nests.

In response to predators, adults flee to nearby shelter. Parents give "chips" excitedly and fly around nest areas when predators are present and sometimes even dive at predators attempting to prey on nestlings or eggs. (Bent and et al, 1968; Sullivan, 1999; United States Department of Agriculture, 2002)

Ecosystem Roles

Dark-eyed juncos, like many other bird species, are an integral part of forested ecosystems and play an important role in maintaining the health and productivity of the forests and woodlands. Members of this species aid in the dispersal of seeds and help to control insect populations. They are occasionally parasitized by brown-headed cowbirds (Molothrus ater). Antibodies of the St. Louis strain of encephalitis have been reported in dark-eyed juncos and there are 26 other genera of parasites that have been reported to use this species as a host. (Bent and et al, 1968; Nolan, et al., 2002)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Junco hyemalis has little, if any, economic importance for humans. This species is an excellent subject for photography and art and provides an enjoyable pastime for many bird watchers. Due to the fact that they are commonly found at bird feeders during migration and winter months, they may play a small part in the sale and production of bird seed, bird feeders and binoculars. Juncos also eat insects that humans may consider pests. (Bent and et al, 1968)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no known adverse affects of dark-eyed juncos on humans.

Conservation Status

Dark-eyed juncos are protected under the US Migratory Bird Treaty Act. They are quite abundant within their geographic range.

Other Comments

There are several distinctive races or groups of races of Junco hyemalis that were formerly considered to be separate species. However, because they interbreed freely where their ranges overlap, they are now treated as a single species. The common names of these former species are still used to refer to these identifiable forms of J. hyemalis. Included in this group are the "Dark-eyed" Junco, the "Slate-colored" Junco, the "White-winged" Junco, Oregon Junco, and the "Gray-headed" Junco. These sub-species were considered separate species until the 1970's when their rank was lowered from species to sub-species. (Barrowclough, 1983; Sibley, 2000)

Contributors

Alaine Camfield (editor), Animal Diversity Web.

Kari Kirschbaum (editor), Animal Diversity Web.

Aynsley Carroll (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Barrowclough, F. 1983. The Audubon Society Master Guide to Birding: Vol. 3. New York: Knopf.

Bent, A., et al. 1968. Life Histories of North American Cardinals, Grosbeaks, Buntings, Towhees, Finches, Sparrows, and Allies: Part II. New York: Dover Publications.

Brewer, R., G. McPeek, R. Adams. 1991. The Atlas of Breeding Birds in Michigan. Lansing: Michigan State University Press.

Dunning, J. 2001. New World Sparrows. Pp. 516-535 in C Elphick, J Dunning, D Sibley, eds. The Sibley Guide to Bird Life and Behavior. New York: Alfred A. Knopf.

Kennedy, D. 2002. "Birds of Stanford" (On-line). Stanford Alumni Association. Accessed March 23, 2004 at http://www.stanfordalumni.org/birdsite/.

McPeek, G. 1994. The Birds of Michigan. Indiana: University Press.

National Audubon Society, 1994. National Audubon Society Field Guide to North American Birds - Eastern Region. New York: Knopf.

Nolan, V., E. Keterson, D. Cristol, C. Rogers, E. Clotfelter, R. Titus, S. Schoech, E. Snajdr. 2002. Dark-eyed junco (Junco hyemalis). Pp. 1-44 in A Poole, F Gill, eds. The Birds of North America, Vol. 716. Philadelphia, PA: The Birds of North America, Inc.

Reader's Digest Association, 1991. Book of North American Birds. New York: Reader's Digest Association, Inc.

Sibley, D. 2000. The Sibley Guide to Birds. New York: Knopf.

Stokes Nature Company, 2002. "Bird Behavior" (On-line). Stokes Birds. Accessed March 23, 2004 at http://www.stokesbirdsathome.com/birding/behav/behavpages/behav110.html.

Sullivan, K. 1999. Yellow-eyed Junco. The Birds of North America, No. 464, 1999, No. 464: 1-23.

The Norman Bird Sanctuary, 2000. "The Norman Bird Sanctuary" (On-line). Accessed March 23, 2004 at http://www.normanbirdsanctuary.org/articles/darkeyedjunco01.shtml.

United States Department of Agriculture, 1991. Forest and Rangeland Birds of the United States - Natural History and Habitat Use. United States Department of Agriculture Forest Service Agriculture Handbook 688.

United States Department of Agriculture, 2002. "Integrated Taxonomic Information Center" (On-line). Accessed March 23, 2004 at http://www.itis.usda.gov/.

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