Life Histories 

A chapter from the electronic book:  Life Histories of Familiar North American Birds

Dark-eyed Junco
Junco hyemalis [Northern Slate-colored Junco]  

Contributed by Stephen W. Eaton
[Published in 1968: Smithsonian Institution United States National Museum Bulletin 237 (Part 2): 1029-1043]

The northern slate-colored junco, or "common snowbird" as persons who know it only in winter often call it, is one of the most distinctive of our common sparrows. With its uniform pale gray upperparts sharply defined against its white belly, aptly described as "leaden skies above, snow below," it is not likely to be confused with anything but other closely related juncos, and then only in the western parts of its wintering range. A friendly little bird that breeds across the continent from Alaska to Labrador and Newfoundland and from the limit of trees southward into the northern United States, it is the summer companion of the canoeist in the Canadian forests and of the mountain hiker in Appalachia. In winter it retreats southward throughout most of the United States in small, congenial flocks of 15 to 25 individuals. These sometimes forage over the snow-covered fields with the tree sparrows searching for the seeds of weeds that escaped the cultivator, and they commonly frequent the yards of homes where food has been put out for them, which they much prefer to scratch from the ground than to pick from an elevated feeder.

Essentially an inhabitant of the more open northern woodlands and forest edges, it is generally common throughout its breeding range in the Hudsonian and Canadian life Zones, except in the deeper woods, but tends to dwindle in numbers toward the north. Typical is E. A. Preble's (1908) comment: "This common species, sometimes called 'tomtit' in the North, is the sole representative of its genus throughout most of the wooded parts of the Athabaska-Mackenzie country. Over this vast region it is a common summer resident, being one of the earliest of the smaller migrants to arrive in spring and a rather late lingerer in autumn."

Francis Harper (1953) notes that "Apparently the numbers of this species diminish rather decidedly toward the tree limit in most parts of northwestern Canada although Porsild (1943:43) reports it well beyond the tree limit at the Mackenzie Delta." Lawrence Walkinshaw writes Mr. Bent of finding the males singing from the treetops 20 to 25 feet above the ground in the spruce bog areas along the Kuskukwim River in Alaska, and adds: "Where the tree line disappeared, so did the juncos."

Spring.--The migrating juncos rush across most of the eastern and midwestern United States about mid-April passing, as they go, their southern relatives already singing on their territories. In Illinois M. C. Shank (1959) reports they build up fat reserves before migrating, but D. W. Johnston (1962) finds the wintering populations leave Wake Forest, N.C., before they deposit any fat. The birds are restless and hyperphagic, and move northward rapidly in flocks of up to 100 individuals. In the East they are often accompanied in the earlier part of the migration by fox and tree sparrows; later along the Saskatchewan River they may be accompanied by tree and clay-colored sparrows (Houston and Street, 1959).

Territory.--The males usually arrive on the breeding grounds well in advance of the start of nesting. During 10 years of observation near Olean in southwestern New York state (Eaton, 1965) I heard the average first territorial singing on March 12, but most males here do not start their territorial song in earnest until about March 21. Some 300 miles farther north Mrs. L. de K. Lawrence writes (in litt.) the juncos arrive at her home in Rutherglen, Ontario in late March or early April, with a mean arrival date of April 2 for 13 years.

The male proclaims his territory by singing from the top of the tallest trees within it, which may be 50 to 75 feet above the ground. Nero (1963) writes from the Lake Athabasca, Saskatchewan region: "On May 18 I found two males apparently engaged in a territorial dispute. The aggressor approached with its breast feathers raised and spread, forming a broad front, and with its tail widely spread and alternately depressed and elevated. Its pinkish bill was very conspicuous against the dark feathers of the head."

Individual territories appear to vary greatly in size, probably because of the scarcity of choice nest sites. The area a male defends vigorously has never been determined experimentally with models and recorded songs, but casual observations of the location of song perches near Olean suggest it is about 2 or 3 acres. Where ideal nest sites are more plentiful, the territories are probably smaller. Each usually seems to include some sort of opening in the forest canopy surrounding a rock outcrop or an exposed soil bank. The species' tendency to build in or near some sort of vertical wall probably helps to explain many unusually placed nests.

Courtship.--The male may continue to sing for some days before a female enters his territory. Mrs. Lawrence (1956) thus describes the early courtship between one of her banded male juncos and a female who appeared 11 days after he arrived in 1953:

Her behavior indicated plainly that her sexual drive had not yet reached high intensity. She faced him as he pursued her, showing him her breast, or hopped aside or away to evade his approach, thus displaying her urge to escape to the point of aggression.

The male pursued her doggedly with wings drooped and tail lifted. Every time when the female withstood him, he stooped and with great intensity pecked at the ground and at his aluminum band on the right tarsus.

Obviously, this pecking at the ground and at the aluminum band, both irrelevant actions in the present situation, were displacement activities, a "substitute behavior". . .as his sexual drive was denied by the female's condition of unreceptiveness.

Generally the first one or two days seem to be spent in establishing and strengthening the pair bond. The male follows his mate about and she feeds within the territory and the two birds remain close together, seldom more than 50 feet apart. Both birds, and particularly the male, display by hopping about the other on the ground with the wings drooping and the tail fanned laterally so that the white outer rectrices are conspicuous. The male now sings much less frequently but he still leaves his mate occasionally to proclaim his occupancy of the property by song from one of his favorite perches.

Nesting.--The junco's ground nest is built by the female, but the male often helps by bringing material for it. Cordelia J. Stanwood, who studied this species extensively at her home in Ellsworth, Maine, wrote Mr. Bent about the activities of a pair building their nest one wet May "under a mass of brush and leaves and sheltered by a small spruce. Both birds brought some of the damp materials and they appeared to care little how wet they were, but the female seemed to do the greater amount of the moulding."

She continues: "The nest site varies according to its situation. I have seen the juncos brooding amongst the roots of a growing clump of gray birches, partially under stumps and rocks, below a tuft of leaves, in a brush heap shaded by small evergreens, beneath bracken, and many within the side of a bank or knoll. The wall of a knoll covered with bird-wheat moss [Polytrichum] or the side of a steep bank just under the overhanging sod seems to be the most typical site for a junco nest. A depression is made or enlarged in the side of the bank or knoll, and the moss or overhanging sod form a natural roof. On a pasture hillside the abode of the junco may be a little cup-shaped structure of straw in the midst of a blueberry patch; in a damp wood it will be a deeper structure with thick walls of moss, twigs, and hay with a substantial lining of fine hay or hair. The brooding female often draws her tail into the nest as the ovenbird does, so that it is well nigh impossible to distinguish the bird or the cradle when looking directly into the nesting cavity."

In wooded country the junco typically nests at the edges of openings in the forest canopy, such as those made by a stream, a logging road, or a clearing. Preble (1908) describes an Athabasca nest that "was built on the steep side of the river bank, and was quite bulky, the outer portion being constructed of fine twigs, strips of bark, and feathers. This foundation inclosed a cup-shaped nest of dry grass, thickly lined with gray dog's hair." E. W. Jameson, Jr. (in litt. to Mr. Bent) describes a nest he found on the Gaspe Peninsula in 1940 "on an east-facing slope of birches and alders. The ground was covered with grass, dead leaves, and bunchberries. The nest itself was in a cavity four inches in underneath a dead stump, the opening protected by a clump of club moss (Lycopodium). Both parents were feeding insects to the four half-grown young."

B. P. Bole, Jr. (1941-1942) describes the nesting of a small colony of juncos on Little Mountain, just east of Cleveland, Ohio, and in a nearby hemlock-studded ravine known as Stebbens Gulch, which is typical for the species in western Pennsylvania and southwestern New York where similar Paleozoic rocks outcrop:

Every one of the junco nests found on Little Mountain was in exactly the same type of place. On this sandstone mesa the brows of the ledges and rocky outlying chunks of puddingstone have curling forelocks of Polypody fern, and it is under the overhanging fronds of these that the Juncos place their nests. As the ferns are on the very edges of the cliffs, it is frequently a matter of some danger to get into positions from which the nests can easily be seen or discovered.

The nests themselves are made of rootlets of various ferns, that of the Polypody being especially favored. There is a thin lining of dry sedges and grass. The whole structure is very compact, and is placed well down in the roots and hanging dead fronds of Polypody. When danger threatens, the female bird tumbles out and downwards into the crevasse facing her; in this she flies for twenty feet or more before rising into the low yellow birches and hemlocks lining the ledges.

The junco often builds in rather unusual situations. Forbush (1929) cites a junco nest on a ledge beneath the gable of a house in Nova Scotia. Wendell P. Smith (1936) writes of a nest of dried grasses and fern stalks and other vegetation 8 feet above the ground in a trellis overgrown with woodbine (Psedera vitacea). Houston and Street (1959) describe a nest in Saskatchewan built in a half-pound tobacco can lying on its side and which contained three junco eggs and three cowbird eggs. Basil J. Wilkinson showed me a nest near Olean, New York, from which young were successfully fledged, in a wind-vane bird-feeder mounted on an 8-foot iron pipe. The base of the triangular feeder was open, and the two sides were glass. The nest was jammed into the apex angle, just as it might have been into a niche in a rock ledge.

Throughout the eastern parts of its range the species is apparently double-brooded. In southwestern New York, I (1965) found two laying peaks, the first at the end of April, the second the first of July. In Maine where Palmer (1949) notes first sets from the first week in May to the first week in June, he states: "A second brood is raised, the eggs being laid from late June to late July." Peters and Burleigh (1951a) found flying young near St. Johns June 9 and add: "Perhaps two broods are raised in Newfoundland for Arnold found a nest with three eggs in the Humble River valley on July 18, 1911."

Eggs.--The northern slate-colored junco usually lays from three to five and rarely six slightly glossy eggs. They are  generally ovate, although some may tend to be either elongated or short ovate. The ground is grayish or very pale bluish-white with speckles, spots, and occasional blotches of reddish-browns such as "Verona brown," "russet," "chestnut," or "Brussels brown," with undermarkings of "pale mouse gray." In most cases the markings are concentrated toward the large end where they frequently form a wreath. There is considerable variation, some being only very faintly speckled, others quite heavily spotted with a few blotches, but in all considerable ground color shows. Often the spottings are quite dull, and the gray speckles may sometimes predominate. One set of eggs in the MCZ is all white and unspotted.

The measurements of 50 eggs of the nominate race average 19.4 by 14.4 millimeters; the eggs showing the four extremes measure 21.1 by 14.2, 20.9 by 16.2, 17.8 by 14.2, and 19.3 by 13.2 millimeters.

Young.--Incubation is apparently by the female alone and usually lasts 12 to 13 days. V. A. Greulach (1934) reports a 12-day incubation period for a nest in Allegany State Park in southwestern New York. In two nests I recently (1965) timed in the same region the elapsed times from the last egg laid to the last hatch were 12 and 13 days, respectively.

Both parents feed the young and attend to nest sanitation. During the first few days they eat the nestlings' fecal sacs, but on the fourth or fifth day start to carry them away instead, usually flying to a perch not far distant and wiping the sac off on a limb. At one of my nests the male always flew to a nearby telephone wire to wipe the sac from his bill; the wire was soon speckled white for a considerable distance before a shower cleaned it up.

V. A. Greulach (1934) comments: "The male removed 27 fecal sacs to the female's 14 during the periods of observation. In all cases where the disposition of the sacs was noted they were wiped off on tree branches. The brooding was apparently all done by the female, and she was not observed brooding after the young were seven days old."

Mrs. Standwood wrote Mr. Bent as follows about a nest she watched from a blind at Ellsworth, Maine: "In the early stages of nursery life the parent birds fed the nestlings 'regurgitated' or partly digested food, together with a few tender moths and caterpillars. Later I saw them feed yellow grubs, millers, many spruce bud-moths, caterpillars, and crane flies. During one period of many hours of watching, the parents fed the young nothing but great numbers of smooth green caterpillars.

"The youngsters begin to open their eyes at the end of the second day and, as in other sparrows, their feathers begin to show about the seventh day. At this time the active youngsters begin to show fear by snuggling down in the nest when a person approaches it. I have seen young birds still in the nest on the 11th or 12th days, but know they could leave earlier if danger threatened them."

Greulach's (1934) young left the nest when 12 days old. In two nests near houses the young I (1965) followed left the nest in 9 days, and I know that a number of these were raised to independence. After leaving the nest the young remain at least partially dependent on their parents for about 3 weeks.

One brood I banded Aug. 3, 1959, just before they left the nest, I was able to follow for an extended period. I saw the father, a crippled bird readily identified, feeding them on August 24 and 27. On August 30, however, one of the young perched on the feeder next to its father and crouched in the begging posture with vibrating wings, but without giving the usual begging call. The old bird stretched upward into the aggressive posture a few times, and when the youngster continued to beg, the father flew at it and chased it a short distance without feeding it. The banded young and their father were still visiting the feeder daily on September 19, about 46 days after leaving the nest. At this time the old bird had almost completed his postnuptial molt; the young still had a few juvenal feathers in the head and their undertail coverts had not quite completed their full growth.

Plumages.--Mrs. Stanwood noted in a letter to Mr. Bent that "When they first peck their way from the shell, young juncos are a reddish, burnt-orange color, and well covered with burnt-umber down." Dwight (1900) on the other hand calls the natal down "slate-gray." He notes the juvenal plumage is acquired by a complete postnatal molt, and describes it as: "Above, drab, plumbeous on crown; sides of head and nape streaked with dull black, the feathers especially of the back edged with bistre. Wings and tail slaty black edged with olive-gray, the tertiaries and wing coverts with dull cinnamon, the greater coverts tipped with buff. Two outer rectrices pure white. Feet pinkish buff, dusky when older. Bill dusky pinkish buff, flesh-color when older and in dried specimens becoming dull ocre-yellow."

He describes the first winter plumage as "acquired by a partial postjuvenal moult in August and September, which involves the body plumage and the wing coverts, but not the rest of the wings nor the tail.

"Above, including wing coverts, sides of head, throat, breast and sides slaty gray, darkest on the crown and veiled with bistre edgings, especially on the back, more faintly with paler brown or ashy gray on the throat. Abdomen and crissum pure white, sometimes faintly washed with vinaceous cinnamon."

The first nuptial plumage is "acquired by wear through which the brown and ashy edgings are finally lost, birds becoming ragged but not much faded by the end of the breeding season. A few new feathers are acquired on the chin early in April, but no regular moult is indicated."

The adult winter plumage is "acquired by a complete postnuptial moult beginning the middle of August. Practically indistinguishable from first winter, but the tertiaries usually edged with gray instead of faded cinnamon, the wings and tail blacker and showing everywhere fewer brown edgings." The adult nuptial plumage is acquired by wear as is the first nuptial, from which it is practically indistinguishable.

The sexes are indistinguishable in the natal down and juvenal plumages. In first winter and subsequent plumages the female is similar to the male, but the gray is much paler and the plumage everywhere more veiled with brown.

Wood (1951) throws new light on the amount of white in the junco's three outer tail feathers. The outer pair are always pure white, but the amount of white on the inner two, most notably on the third pair, increases greatly in the first adult postnuptial molt. Feathers lost or plucked during the first winter are replaced by feathers having the design of those of the succeeding molt, with more white.

Food.--Martin, Zim, and Nelson (1951) say "Juncos, like many other members of the sparrow family, are primarily ground-feeding seed eaters. They are partial to seeds of common weeds. In summer, insects constitute about half or more of their diet." For the northern slate-colored junco "Caterpillars, beetles, and ants seem to be the choice items of the animal diet, the balance being made up of wasps, bugs, grasshoppers, other insects, and spiders." Heading a long list of mostly weed plants whose seeds the junco is known to eat, they list those most frequently identified in their stomach contents as ragweed, bristlegrass, dropseedgrass, crabgrass, pigweed, and goosefoot.

In southwestern New York I have watched them feeding on the fall cankerworm, Alsophila pometaria, in late autumn. During the winter I once saw them eating the seeds of the wild black cherry, and they often eat the seeds of hemlock and yellow birch from the snow surface. Though they usually eat hemlock seeds from the ground, they can and do extract them from the cones on the trees. They feed avidly on the springtails (Collembola) that swarm abundantly about the bases of the trees in February, and they will go out of their way to capture, either on the snow surface or in the air, a small species of gnat that hatches out of the small streams about this time. They also join the early phoebes and bluebirds in preying on the late March or early April hatch of the stonefly, Pteniopteryx nivalis. Francis H. Allen wrote Mr. Bent of a large flock he watched at Cohasset Nov. 2, 1935, whose members "frequently flew into the air to catch flies. The flight was usually, if not always, from trees or bushes and not from the ground. They continued this off and on for nearly an hour."

Voice.--Of the song with which the junco proclaims his territory, F. H. Allen wrote Mr. Bent: "The jingling trill of this junco is well known. It is usually a simple trill, but, as with some other birds whose normal song is a single trill, one will occasionally be heard singing two or even three trills on different pitches but joined together to form a single song." In southwestern New York this song is given mainly in February, March, and April before pair formation and egg laying. After incubation begins it is heard much less frequently, though there is a noticeable recrudescence during late June and early July, and an occasional autumnal upsurge of it in October. As Aretas A. Saunders describes it: "The normal song of the northern slate-colored junco is a simple trill, all on one pitch, or a series of rapid notes, sometimes barely slow enough to count. It resembles that of the chipping sparrow, but is rather more musical in quality. When the notes of the song are slow enough to count they vary, in my records, from 7 to 23 notes, averaging about 12. The length of the songs varies from 1.4 to 2.8 seconds, averaging about 1.9. The pitch varies from E''' to G''''.

"There is a considerable amount of variation in junco songs from the simple trill that is all on one pitch. Some songs vary a bit up or down in pitch, and some vary in time. I believe this bird shows as great a tendency to vary from the normal type of singing as does the towhee. In the Adirondacks I heard a bird singing a song of three prolonged whistles. I chased it about for parts of three days and finally identified it as a junco. Possibly this bird got its song from a white-throated sparrow, but if so it did not sound enough like that bird for me to think it was such."

In notes she sent Mr. Bent, Mrs. Lawrence comments on "the lovely tinkling chorus by the juncos in early spring, as if a myriad of woodland sprites were shaking little bells in an intensive competition," and she syllabizes three variations of the junco song as follows: tilililililili, tililili-tililili, and tuituituitililili. She also describes a "conversational subsong" between members of a pair heard before and during the egg-laying period as "a rough zreet, zreet, zreet followed by a lengthy sotto-voce warbling." E. H. Eaton (1914) quotes Bicknell's description of this as "a whispering warble usually much broken but not without sweetness and sometimes continuing intermittently for many minutes," and which Florence Merriam calls "low, sweet, and as unpretentious and cheery as the friendly bird himself."

Mrs. Lawrence also sent Mr. Bent the following variations she detected in the junco's call notes in different situations:
 

Location:	a simple tit-tit-tit
Alarm 1:	an explosive tchet, tchet
Alarm 2:	bzzz, bzzzz
Scolding:	a smacking tack, tack, tack
Fighting:	tuit, tuit, interspersed with a twanging note and a variety of smacking and buzzing notes
Feeding:	A throaty tulut, tulut seems to serve as a call to come together.

Behavior.--Juncos usually progress on the ground by hopping in fall and winter, but occasionally run in short spurts when chasing a rival or to capture moving food. During the nesting season they may also hop, but more often one sees them walking with short, mincing steps, moving along not unlike a mouse.

F. H. Allen wrote Mr. Bent: "The juncos scratch for food, though not so often nor as vigorously as the fox sparrows do. They scratch by hopping forward and then back with both feet at once. When a thin layer of snow lies on the ground, a bird will scratch away a roughly circular hole 3 or 4 inches in diameter to get at the grain underneath.

"On the whole they are rather scrappy when feeding together and with other birds. Individuals vary in pugnacity, and sometimes females at a winter feeding station will drive off males. On Mar. 3, 1942, in West Roxbury, Mass., a male junco feeding on our lawn with a few other juncos and a number of English sparrows kept his white outer tail feathers showing conspicuously for at least 5 minutes. He held the tail motionless without flicking. As the crowd thinned the white on one side was concealed for a time, and then when he was left alone that of the other side disappeared too. It looked as though the white rectrices were used as a threat on this occasion, a display I had never before seen except in momentary flashes."

Forbush (1929) describes how juncos he watched near the top of Mt. Washington in early August "drank from 'the Stream of a Thousand Falls,' which is formed by the melting of the snow, and then bathed in the frigid waters with much fluttering and splashing of spray, reminding me of other Juncos which I have watched in midwinter, similarly engaged in bathing, but in light dry snow, just as other sparrows take dust baths in hot weather."

W. S. Sabine (1957) comments on the flight behavior of a flock of juncos on their visits to a feeder in Ithaca, N.Y., on late winter afternoons. She found the birds, at what was probably their last feeding of the day, always departed in a regular pattern. As each bird finished feeding it perched quietly for a minute or so at the station, then joined others assembled in an arborvitae clump about 40 feet away where they "made small movements" for about 5 minutes. The whole flock then left the arborvitae together, closely following one another to an adjacent leafless deciduous tree, climbed high in it, and then flew from tree top to tree top along a ridge to the northeast, always in the same direction. She concludes "It seems a reasonable conjecture that the flock had a common goal, and this in turn suggests the hypothesis that a common roost may be a feature of the integration of junco flocks."

Hamilton (1940), also at Ithaca, found juncos roosting at night in winter "on the ground at the base of a Taxus thicket." While night-banding robins near Olean on April 13, I flushed four juncos from roosts 3 to 8 feet from the ground in thick Norway spruces. On Dec. 28, 1960, I flushed a junco after dark from a nest 2 feet from the ground in a hemlock hedge near my house, and on Jan. 25, 1961, I again flushed a bird from the same nest at night. Thus, old nests occasionally function as winter roosting sites.

Field marks.--A slate-colored bird slightly smaller and more slender than a house sparrow, with uniform gray head, back, breast and sides contrasted sharply against the white belly, this junco is seldom confused with any other species except some of its western relatives, such as the Oregon junco, which has a much darker head contrasting with a browner back. The pale bill is conspicuous in the field, and the white outer tail feathers are especially prominent in flight.

Enemies.--Essentially birds of open woodlands and forest edges, the juncos are subject to attack by accipitrine hawks and other predators. Red squirrels, chipmunks, weasels, and martens must take some eggs and young from the nests. Northern shrikes harry the wintering flocks fairly frequently. Cowbird parasitism is apparently not of great moment to the species' reproduction. Friedmann (1963) states:

The slate-colored junco is an infrequently reported host; probably it is molested very slightly by the brown-headed cowbird. Three races have been recorded as victims: cismontanus in British Columbia; carolinensis in Virginia and West Virginia; hymenalis in Alberta, Saskatchewan, Ontario, Quebec, Nova Scotia, New York, Pennsylvania, and Ohio. . . .Both cismontanus and hymenalis have been known to rear young cowbirds.

In the Peace River District of British Columbia, Cowan (1939, p. 59) found that no fewer than four out of five junco nests which were observed were parasitized--evidence which suggests that in this region the bird is a commoner host than it has been found to be elsewhere.

The Communicable Disease Center of the Public Health Service at Atlanta, Ga., has reported antibodies of the St. Louis strain of encephalitis in the northern slate-colored junco. Allen McIntosh of the Animal Disease and Parasite Research Division at Beltsville, Md., writes (in litt.): "There are 61 references to parasites from this host; the following genera of parasites having been reported: Haemoproteus, Leucocytozoon, Plasmodium, Trypanosoma, Eurytrema, Zonorchis, Diplotraema, Taenia, Filaria, Strongyloides, Syngamus, Amblyomma, Analges, Analgopsis, Bruelia Degeriella, Docophorus, Haemaphysalis, Ixodes, Machaerillaemus, Nirmus, Ornithoica, Ornithomyia, Philopterus, Physostomum, Ricinus, and Trombicula.

Fall and Winter.--About the time the first wintry blasts begin to blow across the great coniferous forests of the North, the juncos start moving southward. E. A. Preble (1908) last noted them along the Mackenzie River 50 miles below Fort Simpson on October 16. Houston and Street (1959) say the fall migration along the Saskatchewan River usually ends in late October, but some years the birds are common until mid-November. At Pimisi Bay, Ontario, Mr. Lawrence reports in a letter to Mr. Bent that most of the juncos leave in October, a few late stragglers occasionally remaining into November. E. H. Eaton (1914) writes that in New York state: "In the fall, migrants begin to appear from the 11th to the 28th of September, in the southernmost parts of the state sometimes not before the 4th to the 12th of October. Among the members of the sparrow family, this species rivals the Song sparrow, Vesper sparrow, Savannah sparrow and Chipping sparrow for the place of greatest abundance during the spring and fall migration, probably being as abundant as the Song sparrow in most localities. . . ."

In her studies of the wintering flocks of this junco at Ithaca, N.Y., Winifred S. Sabine (1956) found "that although the migrant individuals which are to become winter residents arrive irregularly over a period of several weeks, they somehow manage to form themselves into distinct, stable winter flocks with mutually exclusive foraging territories." She continues:

The junco flock is an association of birds which is firm in the identity of the individuals associated. . . . In a given small area a single group will be seen and no other. The formation of firm associations and the occupation of definite foraging areas take place at once among the earliest arrivals; it becomes obvious as soon as the first migrants are marked. The late comers are integrated into existing groups. The flock thus formed does not fly about as a unit, however. There appears to be no limit to the size of a foraging group. It may include the whole flock or it may consist of a single bird. The entire flocking procedure is marked by the continual forming and dissolving of groups of unpredictable size consisting of individuals that consort together and are daily visitors at the feeding sites.

*Original Source: Bent, Arthur Cleveland and collaborators (compiled and edited by Oliver L. Austin, Jr.). 1968. Smithsonian Institution United States National Museum Bulletin 237 (Part 2): 1029-1043. United States Government Printing Office

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