Like its relative the Eastern Bluebird, the Mountain Bluebird readily accepts nest boxes, and most of the studies of its breeding ecology are of birds using nest boxes. More cold tolerant than other bluebirds and found in more open habitats in winter, the Mountain Bluebird can at times be seen in large concentrations.
Tree Swallows often try to use nest boxes in areas where Mountain Bluebirds also occur, but the earlier nesting season of the bluebirds and the aggressiveness in nest defense by the bluebirds prevent swallows from taking over the nest boxes.
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Description of the Mountain Bluebird
The Mountain Bluebird has gray to bright blue upperparts, head, and wings, and paler gray or blue underparts.
Males are bright blue above, and paler blue below.
Females are gray to pale blue above, and grayish below.
Seasonal change in appearance
Juveniles are mostly grayish, with spotted underparts.
Mountain Bluebirds inhabit open country with scattered trees.
Mountain Bluebirds eat insects and berries.
Mountain Bluebirds often forage by hovering to spot prey, and then dropping to the ground to capture it. Berries are a more important part of the diet in winter.
Mountain Bluebirds breed from Alaska south through much of the western U.S. They retreat from northern areas to parts of the western and southern U.S. in winter. The population has increased in recent decades.
Mountain Bluebirds become very gregarious in the winter, sometimes occurring in flocks of hundreds.
Mountain Bluebirds are often seen over agricultural fields, where their habit of hovering to seek prey is very effective.
The song is a series of low whistles. A common call is a soft whistle.
- Western and Eastern Bluebirds have reddish underparts.
The Mountain Bluebird’s nest is loose cup of plant materials placed in a natural cavity or nest box, or sometimes in a hole in a cliff or bank.
Number: Usually lay 5-6 eggs.
Color: Pale blue.
Incubation and fledging:
The young hatch at about 13 days and fledge at about 18-21 days, though remaining dependent on the adults for some time.
Bent Life History of the Mountain Bluebird
Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.
Bent Life History for the Mountain Bluebird – the common name and sub-species reflect the nomenclature in use at the time the description was written.
SIALIA CURRUCOIDES (Bechstein)
The mountain bluebird is not so gaudily or so richly colored as the western bluebird, but it is no less pleasing in its coat of exquisite turquoise-blue. As it flies from some low perch to hover like a big blue butterfly over an open field, it seems to carry on its wings the heavenly blue of the clearest sky, and one stands entranced with the purity of its beauty. As Mrs. Wheelock (1904) says: “No words can describe his brilliancy in the breeding season, as he flies through the sunny clearings of the higher Sierra Nevada, or sits like a bright blue flower against the dark green of the pines.” The male certainly is a lovely bird, and the female is hardly less charming in her coat of soft, blended colors.
It occupies a wide breeding range throughout the western half of Canada and the United States, west of the Great Plains. It was formerly called the Arctic bluebird, a decided misnomer, for it is in no sense an Arctic bird, being found in the northern part of its range only in summer. Another old name, Rocky Mountain bluebird, was more appropriate, for it is one of the characteristic birds of the western mountains. Using the latter designation, H. W. Henshaw (1875), who recorded it as very common in Utah and Colorado, and in northern New Mexico and Arizona, says: “I have usually found it during the breeding season in the wild, elevated districts, from 7,000 feet upward, where it frequents the more open spaces, where aspen groves alternate with the remains of pine woods, the broken stubs of which, charred by fires which have swept through again and again, are seen on every side. * * * In the neighborhood of Santa F~, they breed commonly, and here were noticed in the vicinity of houses, seeming in fact to be as familiar and as much at home as does our own bluebird in the East.”
Robert Ridgway (1877) writes of it in the same general region: “Its favorite haunts are the higher portions of the desert ranges of the Great Basin, where there is little water, and no timber other than the usual scant groves of stunted cedars, pinion, or mountain mahogany.”
Mrs. Bailey (1928) says that, in the Sangre de Cristo Mountains in New Mexico, “we found a nest in a grove of aspens on the edge of the open grassy mesa at 10,300 feet, we found families of old and young going about together at 11,000 feet. * * * On August 11, we were much pleased to find a flock of the Bluebirds, together with Red-shafted Flickers and Chipping Sparrows, at 12,300 feet, on a protected slope in the dwarf timberline trees on the south side of Truchas.”
In the Yosemite region, according to Grinnell and Storer (1924), it is chiefly a bird of the Hudsonian Zone, the greater part of the population being found at altitudes above 8,000 feet, “and from there it ranges up to the highest meadows found in our maintains short of timber line.” The highest points at which these bluebirds were seen were at about 10,500 feet, and the lowest were seen at 7,400 feet at Mono Meadow in June.
Russell K. Grater writes to me from Zion National Park, Utah, that “this species is resident during the summer months above 7,500 feet. During the winter months, these birds wander to lower elevations, but seldom enter the deep canyons, apparently preferring more open valley country.”
Aretas A. Saunders (1921b) calls it a common summer resident throughout Montana and says that it “breeds in the Transition zone and less commonly in the Canadian. In the eastern part of the state breeds in the pine hills, farther west, in cottonwood groves, about ranch buildings, and in the more open types of coniferous forests in the foothills of the mountains. In the Canadian zone, it is sometimes found about the edges of mountain parks, but it is never as common at such elevations in Montana as it is in the Transition.”
Spring: At Chelan, Wash., during what they called a typical season, Dawson and Bowles (1909) noted that “the migrations opened with the appearance, on the 24th day of February, of seven males of most perfect beauty.” These observers continue:
They deployed upon the townsite in search of insects, and uttered plaintive note8 of Sialian quality, varied by dainty, thrush-like tsooks of alarm when too closely pressed. * * * On the 15th of March a flock of fifty Bluebirds, all mal~, were sighted flying in close order over the mountain-side, a vision of loveliness which was enhanced by the presence of a dozen or more Westerns. Several flocks were observed at this season in which the two species mingled freely. On the 27th of the same month the last great wave of migration was noted, and some two hundred birds, all ‘Arctics’ now, and at least a third of them females, quartered themselves upon us for a day,: with what delighted appreciation upon our part may best be imagined. The males are practically all azure; hut the females have a much more modest garb of reddish gray, or stone-olive, which flashes into blue on wings and tail, only as the bird flits from post to post.
Norman Criddle (1927), of Treesbank, ~v1anitoba, writes:
The male bluebirds always arrive a few days in advance of the females, but it is not long before the latter appear upon the scene and in an astonishingly short time pairs have taken posses.,ion of a nesting site and the females are taking nesting material into boxes. This haste in constructing a nest is difficult to appreciate because the birds do not, as a rule, actually start domestic duties for some time afterwards. * * *
The male bird is an extreme optimist and nearly any hole meets with his approval, but his mate is not so easily satisfied and many of his selections are discarded as worthless. It is interesting to watch this home seeking, to see the male put his head into a hole followed by the female; should she enter it, he flutters his wings in the height of enthusiasm, but should she turn away unsatisfied, as she does nine times out of ten, then he appears dejected for a few moments, hut speedily recovering, endeavors to entice her into other holes the whereabouts of which he appears to have discovered beforehand.
Old pairs probably remain united providing the male is able to overcome his rivals in battle but not, I suspect, otherwise. The males have been observed to fight vigorously and these combats have continued intermittently for weeks before one bird finally admitted defeat. Thefemale is always a witness to these encounters, in fact she often follows the fighters from place to place, but I have not been able to discover that she takes any part in them and she apparently accepts the victor as a matter of course.
Nesting: All the bluebirds appear to have very similar nesting habits, and the mountain bluebird is no exception to the rule; almost any cavity and almost any location seem to suit them. A. D. Henderson tells me that as far north as Belvedere, Alberta, the mountain bluebird is a common breeder, nesting in flicker holes in the woods, as well as in bird boxes around the buildings. A. Dawes DuBois (MS.) reports two Montana nests; one was in a hole in a burnt stub, 20 feet from the ground; apparently the other was in a hole in a bank of the Teton River, in the prairie region; he saw a pair investigating several holes in the bank and they were “especially interested in one hole, which looked like a kingfisher’s nest tunnel; both of them went into it.”
Mr. Grater tells me that in Zion National Park, Utah, “nests have been located in old trees or in old woodpecker holes. These nests are usually only a few feet from the ground.” Dr. Jean M. Linsdale (1938) reports two very low Nevada nests; one was “in a hole close to the top of a pifion stump 3 feet high,” and the other was “4 feet above the ground on the east side of an aspen trunk.” Another was found “beneath the roof at the corner of a house. * * * The nest was composed of grasses and lined with a few chicken feathers; it held 6 eggs. Both adults were present, and they flew about excitedly or perched on a telephone pole 25 feet away.” Still another “nest was in a cavity made by flickers in the side of a house.”
Referring to the Yosemite region, Grinnell and Storer (1924) write:
At Mono Lake Post Office a pair of Mountain Bluebirds had appropriated to their uses a ledge in a woodshed, entrance to which was gained through a hole in the wall. Here at the height of 10 feet from the ground a loosely woven nest had heen constructed. This nest was made of shreds of bark many of which showed evidence of having been freshly pulled from the trees for the purpose. There were included also numerous chicken feathers from the nearby farmyard. The dimensions outside were roughly 6 or 7 inches in diameter and 2~’i inches in height. The depression for receiving the eggs was 3~ inches wide and 1~4 inches deep. After one brood had been reared this nest was re-lined to receive a second set of eggs.
In addition to the more normal nesting sites in all kinds of cavities in various kinds of trees, in boles in banks, in old woodpecker holes, and in the more recently adopted bird boxes, mountain bluebirds’ nests have been found in crevices in cliffs and among rocks, in old nests, and in almost any available cavity about human habitations and ranches. Miss Catherine A. Hurlbutt says in her notes: “I once observed these birds carrying nesting material into a cliff swallow’s nest under the eaves of a barn, evidently appropriated from the rightful owners, as there were swallows in all the surrounding nests; also another in a chipmunk hole in the bank of a road cut about a couple of feet ‘ibove the surface of the road. I am not sure that the young were successfully raised in either nest.”
According to Mrs. Wheelock (1904) both male and female cooperate in building the nest. The materials used are quite varied; almost any available material seems to satisfy them. R. C. Tate (1926) lists the following material in Oklahoma nests: “Stems of wild oats, rosin weeds, goldenrod, sticktights and milkweeds, and rootlets of prickly pears, stinking sumac, scrub oak and ticke-grass.” And the Macouns (1909) say that a nest found in a clay butte at Medicine Lodge, Saskatchewan, “was wholly composed of the outer bark of the old stems of Bigeiov’ia graveolens, a composite plant that grew in profusion near the site of the nest. It contained seven light blue eggs. Another nest taken under the same conditions along Frenchman river, Sask., on June 2 1st, was built of the outer bark of sage brush (Artemisia cana).”
Eggs: The mountain bluebird lays four to eight eggs to a set. Five and six are the commonest numbers, and sets of seven are not extremely rare. They are usually ovate and are somewhat glossy. The color is pale blue or bluish white, averaging paler than those of other bluebirds; very rarely they are pure white, much less often than those of the eastern bluebird. They are apparently always unmarked. The measurements of 50 eggs irk the United States ~ational Museum average 21.9 by 16.6 millimeters; the eggs showing the four extremes measure 24.9 by 16.8, 21.8 by 17.8, and 19.8 by 15.2 millimeters.
Young: Mrs. Wheelock (1904) writes:
Fourteen days are required for incubation, and in this the male often, but not always, shares. When not on the nest himself he brings food to his mate, calling to her in sweetest tones from the outside before entering the doorway. The newly hatched young are of the usual naked pinkish gray type, looking as like tiny newborn mice as birds. On the second day down begins to appear in thin hairs on head and back; on the fourth or fifth day the eyes show signs of opening; on the sixth day they open, and the down is well spread over the bodies.
Up to this time they have been fed by regurgitation, the adult swallowing each bit first to moisten or crush it; but from the fourth day on fresh food is given occasionally, and from the sixth or seventh day all the food given is in the fresh state, not regurgitated. Crickets, grasshoppers, beetles, butterflies, and worms are their menu, with a few berries. The young Bluebirds double in weight every twenty-four hours for the first week, and in twelve days are growing a respectable crop of feathers, though the bare skins is still distressingly visible. Their breasts gradually take on the soft, mottled light and dark, and the upper parts have a hint of blue among the grayish brown on the wings and tail. One would suppose that this blue on the upper parts would be too conspicuous, but when the youngsters leave the nest and perch on the soft gray of the dead trees, they become almost invisible in the strong sunlight.
On Mount Rainier, on July 18, Taylor and Shaw (1927) discovered a nest of the mountain bluebird 30 feet up in a dead stub, and watched the parents feed the young for over half an hour and summarized their observations as follows:
The young were fed 14 times in 34 minutes, the feedings averaging 2.4 minutes apart. The male fed twice in this time, the female 12 times. The rate of feeding established by this set of observations is approximately 22 times an hour. If this is maintained for five hours in the morning and another five hours in the afternoon, 220 feedings a day would be indicated. But on Mount Rainier at this time of year there were nearly 17 hours of daylight. If the birds averaged 22 feedings an hour for 17 hours, a total of 374 would be indicated. This figure may be closer to the truth than the former one. The male was a shy bird and usually paused on a short branch one to three or four minutes, afraid to go to the nest while the observer was about. The mother was far less cautious. She usually perched for a moment on a branch near the nest and then went directly to it, often entering the cavity and apparently covering the young for a moment.
Probably throughout most of its range the mountain bluebird rears two broods in a season, or tries to do so, perhaps sometimes three; but in the northern portion of its range and on the higher mountains, where the nesting dates seem to be later, it may have time for only one.
Plumages: Ridgway (1907) describes the young male in juvenal plumage, as follows:
Pileum, hindueck, back, and scapulars light brownish gray or drab-gray the interscapular area usually more or less streaked with white; rump and upper tail-coverts light ash gray; remiges and reetrices as in adults, but with distinct terminal margins of white (duller on rerniges), the tertials dusky gray with pale gray or dull whitish margins; middle wing-coverts brownish gray margined terminally with dull white or brownish white; greater-coverts dull blue, margined terminally and edged with pale gray or whitish; a conspicuous orbital ring of white; lores grayish white, suffused with dusky in front of eye, and margined above by dusky; auricular region brownish gray or pale brownish gray, indistinctly 0treaked with paler; throat and upper chest pale gray (passing into dull white on chin), indistinctly streaked with whitish; chest, sides, and flanks squamately streaked (broadly) with grayish brown or drab, the center of the feathers being white; rest of under parts white.
He says of the young female: “Similar to the young male, but blue of wings and tail much duller and (especially that of wings) greener; color of back, etc., browner.”
The postjuvenal molt begins early in August, or earlier, the date varying somewhat according to the date of hatching; I have seen a young bird that had nearly completed the molt on August 20, but usually the first winter plumage is not complete until some time in September. This molt involves all the contour plumage and the lesser and median wing coverts but not the rest of the wings or the tail. In the first winter plumage young birds are practically indistinguishable from adults.
One-year-old birds and adults have a complete postnuptial molt in summer, beginning sometimes before the middle of July, and in some cases it is not completed until well into September. Ridgway (1907) describes the winter plumage of the adult male as “similar to the summer plumage, but blue of upper parts duller, that of pileum, hindneck, back, and scapulars more or less obscured by pale brownish gray margins or tips, the greater wing-coverts and tertials edged with whitish or pale grayish; blue of under parts washed, more or less strongly, with pale brownish gray or grayish brown, especially on chest and sides of breast.”
Of the adult female in winter, he says: “Similar to the summer plumage but, coloration slightly deeper, especially the buffy grayish of under parts.”
There is apparently no spring molt, the colors becoming brighter by the wearing away of the brownish gray edgings. The whole plumage becomes very much worn before the postnuptial molt.
Food: Professor Beal (1915a) examined only 66 stomachs of the mountain bluebird and says: “The contents consisted of 91.62 percent animal matter to 8.38 percent vegetable. This is the highest percentage of animal matter of any member of the thrush family herein discussed and is equal to some of the flycatchers.” The largest item in the animal food consists of beetles; taken collectively they amount to 30.13 percent, but, of these, 10.05 percent belong to three useful families, predaceous ground beetles, tiger beetles, and ladybirds. Weevils amount to 8.11 percent, “the highest record for any American thrush.” Ants were eaten to the extent of 12.51 percent, a record “not exceeded by any other bluebirds or robins.” Other Hyrnenoptera, bees and wasps, amount to 3.80 percent; liemiptera, bugs, to 3.89 percent, consisting of small cicadas, stink bugs, negro bugs, assassin bugs, and jassids; and flies to only 0.92 percent. Lepidoptera, mostly caterl)illars, are a regular article of food, amounting to 14.45 percent for the year. Orthoptera (grasshoppers, locusts, and crickets) are the largest item of food, averaging 23 percent for the year. “Very curiously January shows the greatest consumption, 70.33 percent; August, the normal grasshopper month, stands next with 53.86 percent.”
Of the vegetable food, he says: “As with most of the other thrushes, the vegetable portion of the food of the mountain bluebird consists principally of small fruit. The currants and grapes found were in all probability domestic varieties, but as the grapes were from stomachs taken in December and January, and the currants from one taken in April, they can have but little economic significance.” Other items listed are elderberries, sumac seeds, and unknown seeds. In their winter haunts these bluebirds feed largely on mistletoe and hackberry seeds, on the drupes of the Virginia-creeper and on cedar berries, as well as other wild fruits.
Dr. George F. Knowlton tells me that out of 172 stomachs of this bird collected in Utah 47 contained adults and 4 held nymphs of the beet leafhopper, Eutettix tenellus, a destructive pest.
Grinnell and Storer (1924) describe its feeding habits very well, as follows:
In the nesting season and indeed through most of the year the Mountain Bluebird subsists upon insects. Theee are captured in two totally different ways, according to the habits of the insects sought. For beetles and others which fly through the air a bluebird will take position on a boulder in a meadow or on the low outswaying branch of some tree and dart after the insects which pass by. For insects which live on the ground, such as grasshoppers, the bird mounts 10 to 20 feet into the air over the grassland and then by fluttering its wings rapidly, hovers in one place for several seconds and intently scans the surface below, like a Sparrow Hawk when similarly engaged. If something is sighted the bird drops quickly to the ground and seizes it; otherwise the bluebird moves a short distance to a new location which is given similar scrutiny. It thus examines the ground in a manner recalling that employed by the robin though from an aerial location where its scope of view is much greater though less thorough.
This hovering habit has been noted by numerous observers and seems to be characteristic of the species; it seems to prefer this method of foraging to using posts and wires as lookout points, from which to dart down onto its prey, as the other bluebirds generally do.
Behavior: The mountain bluebird is not a swift flier, probably not making more than 17 or 18 miles per hour on its ordinary short flights. John G. Tyler (1913) says that “a company of these bluebirds in flight may be identified at a distance by their peculiar manner of poising for a few seconds on rapidly beating wings, then flying ahead in undulating swoops. They are often seen in company with Linnets, the two species frequently perching for many minutes in neighborly manner on telephone wires. The bluebirds take wing one at a time and fly ahead at the approach of an intruder, the different units of a flock sometimes becoming quite widely scattered.”
Claude T. Barnes writes to me: “It is interesting to see them alight upon snow-covered telephone wires. The snow bothers them, and the flock will not alight until one of their number has ventured upon the wire and shaken himself, thus jarring off the snow.”
These, like other bluebirds, are ordinarily gentle birds, but they are able to defend their nests against aggressors and can become aggressive thejriselves in the competition for nesting sites, or even drive out the rightful occupants. Dr. Alden H. Miller (1935) tells how he saw them drive a pair of hairy woodpeckers from their partly finished hole and appropriate it for themselves:
During the first day, June 5, commotions were frequently noticed at the Woodpecker’s tree. The trouble was instigated by a pair of Mountain Bluebirds (Sielio currucoides). Whenever the Woodpeckers alighted near the holes, both Bluebirds attacked by diving at them, uttering harsh notes and apparently snapping their bills. Such attacks often lasted five minutes. Evidently the Woodpeckers were too much disturbed by them, possibly also by us, and deserted. During the last two days at camp, no more fights were seen and the Bluebirds were carrying nest material to the tree. The Woodpeckers stayed in the grove, often close to camp, but did not go to the trees near the nest. Since the Bluebirds were just beginning to build, the. Woodpeckers were clearly the first occupants and had been dispossessed. Irrespective of other factors which may have contributed to their departure, there was no doubt of the intention of the Bluebirds to displace them.
On June 6 the female Bluebird went to an unfinished Robin’s nest just over the tent and settled in it, much to my surprise. She plucked material from the margin and flew to her own nest hole. The Robins added to their nest later that day. The Bluebird, symbol of happiness and gentleness, became to us a different character, whose actions, viewed anthropomorphically, were aggressive and piratical. Interspecific competition for nest material and nest site were enacted before us.
Voice: The song of the mountain bluebird seems to have appealed quite differently to various observers. Dawson (1923) evidently did not hear it at its best, or did not appreciate it, for, after describing its call and alarm notes, he says: “Other songs the birds have none. * * * The entire song tradition, including the ‘delightful warble’ attributed to the bird by Townsend, appears to be quite without found ation.” And that close observer of bird songs, Aretas A. Saunders, writes to me: “In all my experience with this species in Montana, I never heard it sing. On a number of occasions I camped near nesting bluebirds and heard morning awakening songs of various other birds, but nothing from the bluebird. It may be, as Weydemeyer suggests, that some individuals do not sing, or perhaps I never happened to be awake at the right place and time to hear it.”
Ralph Hoffmann (1927) says: “The Mountain Bluebird at all times is singularly silent. An occasional low terr is its commonest note, uttered by a flock in flight. The only song which the writer has heard is the repetition of a few short notes, like the syllables k~ k~ or k?l, k~, k~. When concerned about their young, the parents utter a vigorous tschuk, tschulc.”
On the other hand, some observers have been more favorably impressed. Francis II. Ailen says in his notes: “On several occasions late in September and early in October of 1929, in Colorado, I heard the song of this species. It was a beautiful, clear, short warble, higher-pitched than that of S. sialis and hardly suggesting it. The call notes were sweet and soft, very much like those of the eastern bluebird, but not so clear or so loud.”
Claude T. Barnes writes to me from Utah: “Sitting on a clothesline, a female bluebird resented my approach by a click, several times repeated; then at last it sang its very soft, charming song: Trill, trill, trill, a mellow roll uttered without opening its bill. The number of trlls varied from one to half a dozen, but I am positive the bird never once opened its bill during the ten minutes that I watched it without taking the glasses from my eyes. This habit is, no doubt, somewhat responsible for the subdued nature of the lovely bird’s song.~~ Mrs. Wheelock (1904) refers to the song as “a sweet clear ‘trually, tru-al-ly,’ like that of the Eastern species, and a mellow warbie.” And Winton Weydemeyer (1934a) writes:
On frequent occasions during the last seven summers I have forsaken the comfort of my bed to enjoy their subdued, gentle singing. For one must be an early riser indeed if he wishes to hear the Mountain Bluebird’s song. Singing commences in full darkness, and continues for a few minutes to as much as an hour, ceasing soon after daylight. * * * Only once during t~e past seven years have I heard the bird’s song at any other time of the day: At 9 o’clock on a dark, rainy morning in March of 1932, a Mountain Bluebird gave weakly a few snatches of its usual daybreak song.
In form, the song is almost a replica of the familiar caroling of the Western Robin; but it is given very softly, crooningly, with an unmistakable quality of the Bluebird’s gentle call. Though I have not determined the distance at which the singing can be heard, I doubt if it is audible at seventy yards. The notes are repeated over and over, without a pause, for as much as thirty minutes at a time.
Because of the marked resemblance to the song of the Robin, * * * the song of the Mountain Bluebird appears to be a possible illustration of retrogression in the evolution of bird song. It seems probable that the song, at some time in the past, was louder arid more varied, and was sung more commonly, than it is now; and that it is gradually being lost, even as the species is losing other thrush-like characters. If this be so, it is possible that some or all of the Mountain Bluebirds in some parts of their breeding range are already songless, as the testimony of many writers indicates.
Field marks: The male mountain bluebird is unmistakable in his beautiful coat of plain cerulean or turquoise blue, with only a shading of dusky in his wing tips. The female is modestly clad in a pale brownish or buff gray, with a tinge of bluish on the upper surface. Both can be distinguished from the western bluebird by the entire absence of chestnut. The blue is much paler than in most other blue birds, except the lazuili bunting, which is a smaller bird and, has white wing bars.
Enemies: Qther hole-nesting birds are competitors for nesting sites, notably flickers and English sparrows, and probably the ordinary predators take their toll. Mr. Criddle (1927) says of these two enemies: “Flickers are quite important factors in the survival of young bluebirds, even though they often provide the adults with nesting holes. Two instances came to my attention of the parents being driven from their nests by flickers, in both cases resulting in the deaths of the young by starvation. * * * Male mountain bluebirds are able to defend their nests against all intruders of their own size, this includes the house sparrow which has somewhat of a reputation for ousting other species. The sparrow, however, is no match for the bluebird in open fight and despite its persistency, it has never been observed to get possession of a nesting box occupied by the latter.” He has seen the bluebirds drive away kingbirds, crows, and squirrels, but the flickers are generally too formidable. House wrens have nested near the bluebirds, but he has never seen the former do any damage to the latter. Among the enemies of the bluebirds he mentions Cooper’s and sharp-shinned hawks and weasels but thinks the latter are not so destructive as the squirrels, which are better climbers. Cold rain and snowstorms early in spring or late in fall often prove fatal to young, or even adults.
Dr. Friedmann (1938) could find only one record of cowbird parasitism; a nest found by T. E. Randall in Alberta contained four eggs of the bluebird and one of the Nevada cowbird.
Fall: Early in August, family parties begin to gather into small companies or larger flocks and gradually drift along southward from the more northern portions of their summer range, the migration continuing well into November. They do not ordinarily move in compact flocks. At this season one often sees detached companies of mountain, western, or chestnut-backed bluebirds wandering about the open country, sometimes loosely associated with sparrows, juncos, warblers, flickers, and other small birds, on their way south. But many bluebirds spend the winter in the greater part of their summer range, moving from the mountains down into the valleys.
Winter: Ralph Hoffmann (1927) says: “In winter any extensive open country, such as the wheat fields of interior California, is visited by flocks of mountain bluebirds.”
These bluebirds do not wholly desert the higher elevations even in winter; Russell K. Grater writes to me: “During late February 1942, I had occasion to be on ski patrol into Cedar Breaks National Monument. At that time the snow was several feet deep on the open. The altitude is around 10,300 feet. Here on the snow fields were many mountain bluebirds, darting hither and yon, apparently catching something on the snow. An investigation revealed that the snow was literally alive with hundreds of tiny winged insects and the birds were making the most of the abundance of food. These birds were observed commonly throughout the open country on this trip.”
George F. Simmons (1925) says that, in the vicinity of Austin, Tax., the mountain bluebird “appears in these comparative lowlands usually during very cold weather or during the rare snowstorms and accompanying freezes, which remain for several days.”
Range: Western North America from Alaska and northern Canada south to northern Mexico.
Breeding range: The mountain bluebird breeds north to east central Alaska (Fairbanks, Lake Mansfield, and Ketchumstock); southwestern Yukon (Dawson, probably; Selkirk, and Lake Lebarge); possibly southwestern Mackenzie, since it has been taken in summer at Fort Franldin, Great Bear Lake (type specimen), and at Hay River and Fort Resolution on Great Slave Lake; north central Alberta (Lesser Slave Lake and Boyle); southern Saskatchewan (Cypress Hills, Wood Mountain, and Yorkton); and southern Manitoba (Aweme, Lake St. Martin, probably, and Richer). East to southeastern Manitoba (Richer); western North Dakota (Fort Union, Arnegard, and Medora); western South Dakota (Short Pine Hills and the Black Hills); northwestern Nebraska (Pine Ridge and other points in Dawes and Cheyenne Counties); eastern Wyoming (Laramie Mountains, Cheyenne, and Sherman); central Colorado (Estes Park, Denver, Colorado Springs, Pueblo, and Fort Garland); extreme northwestern Oklahoma (Black Mesa region); and the mountains of New Mexico (Halls Peak, Pecos Baldy, Ribera, and the Sacramento Mountains). South to southern New Mexico (Sacramento Mountains and Silver City); central Arizona (White Mountains and Mogollon Mountains); and southern California (San Bernardino Mountains). West to central southern California (San Bernardino Mountains), the Sierra Nevada and Cascade ranges in California (Walker Pass, Sequoia Park, Fyffe, Mount Sanbedrin, and Mount Shasta); western Oregon (Swan Lake, Fort Klaiuath, Saddle Mountain, and Portland); western Washington (Mount St. Helens and Mount Rainier); western British Columbia (Horseshoe Lake, Oyster River, Vancouver Island, Smithers, Atlin, and Bennett); and eastern Alaska (Taku River, McCarthy, and Fairbanks).
Winter range: The mountain bluebird winters north casually to central Washington (Yakima and Spokane), southwestern Idaho (Meridian); northern Utah (Salt Lake City and Provo), and central Colorado (Grand Junction and Denver). East to central Colorado (Denver, Colorado Springs, and Pueblo); eastern New Mexico (Las Vegas and the Guadalupe Mountains); western Chihuahua (Pacheco); and eastern Sonora (Nacori and Alamos). Irregular or casual in winter east to eastern Kansas (Manhattan); Oklahoma (Caddo); and Texas (Bonham, Corsicana, San Antonio, and Corpus Christi); and Nuevo Lc6n (Monterrey). South to southern Sonora (Alamos). West to Sonora (Alamos and Sonoyta); northern Lower California (San Ram6n, Rancho San Pablo, and Guadalupe Island, one record); the coast valleys of California north to San Francisco Bay (San Diego, Santa Barbara, occasional on Santa Cruz Island, Salinas, and Sonoma); east of the Coast Range in Oregon (Medford and Portland); and east of the Cascades in Washington (Yakima).
Since the first decade of this century the mountain bluebird seems to have increased and spread eastward, at least in the northern part of its range. At Eastend, Saskatchewan, it is reported to have increased noticeably between 1910 and 1922; at Aweme, Manitoba, it was “rare” in 1890, and “common” before 1928; at Lake St. Martin, Manitoba, in 1931 the Indians reported it to be a comparatively recent arrival. A young bird, thought to be this species, was shot but not recovered, June 10, 1931, at Churchill and an adult specimen was collected there on August 6,1938.
Migration: Some early dates of spring arrival are: Nebraska: Hastings, March 5. North Dakota: Charlson, March 19. Manitoba: Aweme, February 28. Saskatchewan: Indian Head, March 16. Colorado: Fort Collins, February 12. Wyoming: Wheatland, February 28. Montana: Helena, March 12. Alberta: Camrose, March 14. Utah: Corinne, March 8. Idaho: Meridian, February 17. British Columbia: West Summerland, February 14; Atlin, April 13. Yukon: Dawson, April 20. Alaska: Dyer, April 20.
Some late dates of fall departure are: Yukon: Carcross, September 24. British Columbia: Atlin, September 24; Chilliwack, November 6. Alberta: Glenevis, October 15. Idaho: Priest River, October 13. Montana: Fortine, November 10. Wyoming: Laramie, November 3. Utah: Ogden, November 4. Colorado: Walden, November 5. Saskatchewan: Eastend, October 14. Manitoba: Brandon, October 28. North Dakota: Argusville, October 11.
One very interesting banding record is available. A young bird banded at Camrose, Alberta, on June 9, 1939, was caught previous to November 30, 1939, at Wingate, Runnels County, Tex.
Casual records: At Cape Etolin, Nunivak Island, Alaska, three specimens were collected on September 23 and 28, 1927. At Barrow, Alaska, two specimens were collected on June 5, 1930, and one on May 20, 1937. All five of these birds were femalcs. There are two records for the species in Minncsota: a pair seen closely on April 5 and 7, 1935, near St. Cloud; and one to five seen from December 1942 to March 14, 1943, at Duluth.
Egg dates: Alberta: 8 records, May 21 to June 19.
California: 34 records, April 5 to July 17; 17 records, June 9 to June 18, indicating the height of the season.
Colorado: 30 records, May 2 to June 12; 18 records, May 18 to June 4.
New Mexico: 6 records, May 5 to June 6.