A western counterpart to the Eastern Bluebird, the Western Bluebird occupies parklike areas with trees and nest cavities over much of the western U.S. Some Western Bluebirds make altitudinal movements during the year, while others make short migrations, traveling during the day.
Some nesting pairs of Western Bluebirds have a helper or a helper pair that assists with feeding the young. If the helper pair consists of adult birds, the nesting pair typically fledges more young than nests without helpers. Nest parasitism by Brown-headed Cowbirds is very rare.
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Description of the Western Bluebird
The Western Bluebird has gray to bright blue upperparts, head, and wings, and variably reddish underparts.
Males are bright blue above, with some reddish on the back and bright reddish underparts. Length: 7 in. Wingspan: 13 in.
Females are gray to pale blue above, often with some reddish on the back, and pale reddish below.
Seasonal change in appearance
Juveniles are mostly grayish, with spotted underparts and back.
Western Bluebirds inhabit open country with scattered trees, as well as pine or oak woodlands, and streamsides.
Western Bluebirds eat insects and berries.
Western Bluebirds forage by observing for prey from low perches, and then flying to the ground to capture it. Berries are a more important part of the diet in winter.
Western Bluebirds breed from southwestern Canada 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 declined in recent decades.
Western Bluebirds have declined in part due to fire suppression altering their habitat.
Within migratory populations, males arrive on the breeding grounds first in the spring.
The song is a series of call notes heard at dawn. A common call is a hard whistle.
- Mountain Bluebirds are all or mostly gray or blue, and Eastern Bluebirds lack reddish on the back and have a whitish or reddish throat.
The Western Bluebird’s nest is a loose cup of plant materials placed in a natural cavity or nest box.
Number: Usually lay 4-6 eggs.
Color: Pale blue.
Incubation and fledging:
The young hatch at about 13 days and fledge at about 20 days, though remaining dependent on the adults for some time.
Bent Life History of the Western 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 Western Bluebird – the common name and sub-species reflect the nomenclature in use at the time the description was written.
SIALIA MEXICANA OCCIDENTALIS Townsend
The 1931 Check-list states that the western bluebird breeds from southern British Columbia to southern California, but it may breed farther north. Theed Pearse, of Courtenay, tells me that the large numbers that pass through that portion of Vancouver Island indicate that the breeding range extends considerably north of that point. The range extends eastward to northern Idaho and western Montana.
Samuel F. Rathbun records it in his notes as a common species about Seattle, Wash., from early in spring to late in fall, and of frequent occurrence during the winter. It is found in logged-off sections, along highways, and about isolated farms and clearings, where there are a few tall dead trees.
in the Lassen Peak region of California, according to Grinnell, Dixon, and Linsdale (1930), “in summer western bluebirds were to be observed about clearings and in those places where the cover of trees was sparse. Individuals and pairs when not in flight were most often seen perched in the tops of dead or dead-topped trees.”
Grinnell and Storer (1924) state that, in the Yosemite region, “in the spring and summer months the local Western Bluebird population is confined almost entirely to the blue oak belt of the western foothills and hence within the Upper Sonoran Zone. * * * In the fall months, however, Western Bluebirds appear at many up-mountain localities not previously tenanted by the species.”
Howard L. Cogswell writes to me: “On May 6,1936, I saw one pair accompanied by an immature on the oak-bordered Flintridge Golf Course, near Devil’s Gate Dam, Pasadena; and on June 28, 1940, I saw a pair feeding half-grown young in the San Gabriel River Sanctuary, south of El Monte, in a typical Lower Sonoran riparian association, at an altitude of only 300 feet above sea level.”
Courtship: The only information I can find on the courtship of the western bluebird is contained in a short note from Theed Pearse. He watched a pair mating; the male, that had been sitting beside the female, mounted her; and then the female mounted the male, which then flew away. A similar performance was seen a few days later; the male seemed to flatten himself out for the female to mount.
Nesting: The nesting habits of the western bluebird do not differ materially from those of its eastern cousin. The only two nests that I have seen were in nowise out of the ordinary; one, found on May 14, 1911, near Tacoma, Wash., was in a cavity 10 feet from the ground in a dead oak stub; it contained four eggs; the other, in Ventura County, Calif., on April 7,1929, was in an old hole of a California woodpecker on the under side of a limb of a sycamore tree. The nests were very simply and carelessly built struct.ures of dry grass and a few feathers.
Referring to the Yosemite region, Grinnell and Storer (1924) write:
Old woodpecker holes are occupied when available, but failing to find one of these the birds will use some naturally formed opening in a tree. The decay of stubs of medium-sized branches often results in the formation of cavities in the heart wood of an oak which are appropriate in form and size for use by the bluebirds. * * * The nest found near Lagrange was in a blue oak on a hill top. It was in a naturally rotted-out cavity at a height of 9 feet from the ground. Distant but 17 inches in the same stub was the nest of a Plain Titmouse. The bluebird’s nest was 6~4 inches below the rim of the opening and the sparse lining upon which the 4 eggs lay consisted chiefly of dry foxtail grass. Another nest seen at Smith Creek, east of Coulterville, was 14 feet above the ground in a black oak. A natural cavity about 11 inches deep by 5 inches in diameter had been filled for a depth of 4 to 5 inches with soft materials. Entrance was afforded to the nest on two sides; on the one side was a hole about 2y, inches in diameter, while there was a much larger opening on the other side, so that the nest was easily visible from without.
In the Point Lobos Reserve, Monterey County, according to Grinnell and Linsdale (1936), “all the nests were in cavities in pines or pine stumps at heights ranging from five to forty feet, averaging twenty-two feet. On the few occasions when material was seen being carried to the nest, the female was doing the work. Usually, however, the male was present and showed an interest in the procedure. Once a male at a nest spent more time there than did the female, going in and out and moving the materials. Several times a male was seen to feed his mate.”
Western bluebirds are as easily encouraged to nest near our homes in bird boxes as are their eastern relatives; here they often meet serious competition with violet-green swallows or western house wrens, but the bluebirds are generally the masters of the situation; they can defend their homes against such intruders and have been kno~vn to drive out the swallows from their occupied nest. Where natural cavities, woodpecker holes, or bird boxes are not available the bluebirds will build their nests in any suitable cavity in a building, or even in a cliff swallow’s nest. They are very persistent in their attempts to raise a family; if a set of eggs is taken the birds xviii lay a second set of eggs within a very short time and, if necessary, a third set.
Eggs: The western bluebird has been known to lay three to eight eggs to a set; probably sets of three are incomplete; sets of four, five, and six seem to be almost equally common; I have heard of only one set of eight, in the collection of Sidney B. Peyton. The eggs are pale blue and practically indistinguishable from those of the eastern bluebird in every way. The measurements of 50 eggs in the United States National Museum average 20.8 by 16.3 millimeters; the eggs showing the four extremes measure 23.3 by 16.3, 20.1 by 17.5, 19.1 by 16.8, and 20.3 by 15.2 millimeters.
Young: The period of incubation does not seem to have been definitely determined, nor does it seem to be known how long the young remain in the nest; probably both of these periods are similar to those of the eastern bluebird. Incubation of the eggs and brooding of the young seems to be done entirely by the female. Harriet Williams Myers (1912) watched a nest near Los Angeles for 1 hour and 35 minutes. “During this time the female left four times, staying away five minutes once and eight the other times. Her times for brooding were respectively twenty-two, eighteen, ten, and twentyfour minutes. Almost invariably during this and subsequent watchings the female did not leave the nest until the male came to it.” Four days later, during an hour and a half, “the female left the nest four times as before. The longest interval of staying away was twenty-seven minutes; the shortest two minutes. The longest interval of brooding was sixteen minutes; the shortest thirteen.” Eight days later when there were young in the nest, she watched it for an hour. “During the hour fifteen trips were made to the nest, the feeding being very equally divided. In fact, with two or three exceptions, the birds were both at the nest at once each of the fifteen times.”
James Ivlurdock has sent me a photograph of a western bluebird at its nest in a hole in a yellow-pine log. While he was photographing he noticed that two males and one female were feeding the young; he and his companions saw the two males enter the nest. He writes to me: “One at a time they flew directly in front of us and entered the nest, one coming out while the other went in. Both had food in their bills.”
Kenneth Racey (1939) writes: “The bluebirds are most amusing in the way they keep house and care for the young and they go through the same performance each year. The first brood is brought off and then within a few days the old birds are busy laying and brooding again. When the second brood fledges, both families, usually eight young and the two adults, join in one flock and remain in the neighbourhood, visiting the garden every few days until it is time to leave for a warmer climate. The young of the first family are fed and cared for while the second clutch of eggs is being incubated.”
Plumages: T he sequence of plumages and molts evidently parallels that of the eastern bluebird. The adults of the two species are more unlike than are the juvenals. In the western bluebird the sexes are distinguishable in the juvenal plumage. In the young male the head and neck are plain sooty gray, the interseapular region is from “Verona brown” to “olive-brown,” conspicuously streaked with white, and the rump, upper tail coverts, and the lesser and median wing coverts are dull slate color; the breast and sides are “warm sepia,” heavily streaked or spotted with white; the wings and tail are much like those of the adult female, but the blue is brighter and the tertials are margined with pale grayish brdwn. The young female is similar to the young male, but all the colors are paler and duller, and the breast is more heavily streaked with white. Ridgway’s (1907) account indicates that only the young female has the interseapular region streaked with white, but all the young birds in the considerable series of both sexes that I have examined are so streaked, and Dawson’s (1923) account agrees with my findings.
The postjuvenal molt begins early in July in some birds and not until the middle of August in others, this probably depending on the date of hatching. This produces the first winter plumage, in which young birds become very much like the winter adults of the respective sexes. Ridgway (1907) says of the young male at this season: “Similar to the adult male in winter plumage, but the blue lighter and less violaceous and (except on rump, upper tail-coverts, rectrices, and remiges) duller, the feathers of pileum and dorsal region more broadly tipped with grayish brown; chestnut of under parts rather lighter, the feathers wit.h paler tips.” The first winter female differs from the adult winter female in about the same way.
There is apparently no spring molt, but the grayish-brown edgings have worn away, giving a brighter appearance; first-year birds can then be distinguished from adults by the juvenal wings and tails, which have been retained through the winter.
One-year-old young birds and adults have a complete postnuptial molt in August and September, at which old and young become indistinguishable. Ridgway (1907) says that, after this molt, the blue of the upper parts of the male is “slightly obscured by narrow brownish tips to the feathers, and that of the chest and breast by pale grayish brown tips.” These tips wear away during winter, producing the full spring brilliancy. Of the adult winter female, he says: “Similar to the spring and summer plumage, but brighter in color, the pileum and dorsal region decidedly bluish, and ruddy brown of under parts more chestnut.”
Food: Professor Beal (19 15a), in his food studies, treats the western bluebird, the chestnut-backed bluebird, and the San Pedro bluebird all together, as subspecies of the Mexican bluebird. In the 217 stomachs examined, the food was found to consist of 81.94 percent animal and 18.06 percent vegetable matter. Among the animal food, grasshoppers formed the largest item, with an annual average of 21.29 percent. Caterpillars were a close second, averaging 20.25 percent. Useful beetles, mostly Carabidae with a few ladybirds, amounted to 8.56 percent; and other beetles, all more or less harmful, accounted for 15.44 percent of the food. Ants constituted 5.38 percent, and other Hymenoptera only 1.26 percent; no honey bees were found. Flies and a few other insects, spiders, myriapods, angleworms, snails, and sowbugs were eaten in very small quantities.
The vegetable food was made up mainly of fruit, mostly all wild species or waste cultivated fruits picked up late in the season. “Rubus fruits (blackberries or raspberries) were found in 4 stomachs, prunes in 1, cherries in 1, and figs in 3.” Elderberries and mistletoe berries proved to be favorite foods; weed seeds were eaten sparingly, no grain of any kind was found, and a few other items, such as seeds of poisonoak and other Rhus seeds, made up the balance. Of the food of the nestlings, he says: “The real food consists of grasshoppers and crickets, 90 per cent, and beetles, 3 per cent, the remainder being made up of bugs, caterpillars, and spiders. * * * The remains of 11 grasshoppers were found in one stomach and 10 grasshoppers, a cricket, and a beetle in another.”
Theed Pearse tells me that he has seen western bluebirds feeding on the berries of the Virginia-creeper, taking them from the vines; he has also seen them “hawking” insects in the air with a very pretty butterfly flight. They often dart out into the air from some high perch and catch the insects in flight, but more often they watch from some low perch and flutter down to catch their prey on the ground, or hover along over the tops of the herbage to catch the flying insects that they have disturbed. Frank A. Pitelka (1941) saw some of these birds soaring in a strong wind while feeding; he writes:
The bluebirds would fly to a position in the up-draft some 6 or 8 feet above the ground, there hover for a second or two, and then soar for a few seconds. On a number of occasions, one or two of them remained in a soaring position without movement of wings for 6 to S seconds. The birds were foraging for insects, which they caught by dropping quickly from their position in the air. It appeared that the wind was blowing insects upward over the hill slightly above the grass. The bluebirds, hovering or soaring and looking down, watched for them; when prey was sighted, the bird turned about face and flew back to catch up with it. Such a behavior was observed on both the open slopes and in the draws. As many as four birds were noted hovering and soaring at one time in a few yards of area.
Dr. Grinnell (1904) describes an interesting method of feeding, as follows: “In Palm Canyon great numbers were in evidence among the giant palms. A dozen or more would be seen clinging to each pendant cluster of dates obviously attracted by the fruity outside pulp. While thus feeding upon the fruit of the palms, the noise made by the seeds dropping into the dry brush at the bases of the lofty trees was so great as to give the impression, before the true cause was discovered, that some large animal was trampling through the undergrowth.”
Grinnell and Storer (1924) give an account of how these bluebirds help to spread the seeds of the mistletoe. Only the soft pulp of the berry is digested, and the seed, which is coated with a film of mucilaginous material, passes through the bird’s alimentary canal in condition to stick where it falls. Should the seed happen to fall on the right kind of host tree, it would, under proper conditions, germinate and start a new plant of this objectionable parasite. The birds swallow so many of these seeds that probably some new plants are started each year. They write of the feeding process: “The birds individually will seek perches about clumps of mistletoe, either on adjacent parts of the tree or on the twigs of the parasite itself. Berries will be picked off and swallowed in rapid succession. Each bird, as it gets its fill of berries, flies to some nearby perch and sits there quietly. The process of digestion is a rapid one, and before many minutes have elapsed enough of the berries will have gone from the bluebird’s gullet into its stomach to permit of further feeding. Thus the day is spent, alternately in feeding and digesting.”
Behavior: The same authors have this to say on this subject:
In general demeanor the Western Bluebird is much like other members of the thrush family, being of deliberate or even phlegmatic temperament. When perched it sits quietly, not hopping about as do many small birds such as sparrows and warbiers. It ordinarily seeks a perch which will command a wide field of view, as on some upper or outer branch of a deciduous tree. * * * Upon taking to flight bluebirds make off in the open, high in the air, uttering their soft call notes now and then as they fly. The high course of flight and the repeated flight calls are suggestive of the behavior of linnets under similar circumstances. Sometimes the flight is so far above the earth that the birds are quite beyond the range of vision of an observer stationed on the ground, only the mellow call notes giving indication of the passage of the birds overhead, When bluebirds are in flocks the formation is never compact or coherent; individuals move here and there among their companions and single birds or groups join and depart at intervals.
Voice: Several observers have condemned the song of the western bluebird with faint praise. Dawson (1923) says: “The Eastern Bluebird warbles delightfully; therefore, the Western Bluebird ought to: but it doesn’t. In an experience of some thirty-nine years, the author has never heard from the Western Bluebird’s beak an utterance which deserves the name of song, or anything more musical than the threefold miu.” Ralph Hoffmann (1927) writes: “In the breeding season the male utters a low chu, chu, chu, apparently his only song, but before dawn a camper among the pines hears a chorus of the rich call notes repeated from all sides as if from birds flying about in the darkness.” And Grinnell and Storer (1924) say that the “song is a very simple affair, just the common call notes uttered over and over again with monotonous persistence.”
Winton Weydemeyer (1934), however, gives this bluebird credit for more musical ability, and contributes the following account of the singing of a bird near his house at Fortine, Mont.:
The first attempt at singing was noted at 4:40 A. M. (in full darkness) on April 19. For several minutes without pause one of the birds from a perch rendered an endless song consisting of the common call note, few, repeated over and over, regularly but with varying inflection. On succeeding mornings the notes gradually became more varied. The following description was jotted down on t.he morning of April 26: “Bluebird from perch began singing at 4:35 (quite dark), sang for about 40 minutes. Sang without pause for about fifteen minutes first; later snatches of song successively shorter, intervening pauses longer. Song a succession of call notes (3 different phrases); notes same as given separately in daytime, but connected in a series to form a typical ‘song.’ Song louder and more energetic than that of the Mountain Bluebird, just as the call notes are louder and more vigorous. Tempo much like that of Robin’s song. F-few, f-ftw, f-ftw f-ftw, cA-gA, ftw, f-ftw, eh-eh, JAw, eh-eh, JAw, f-JAw . . . The eh-eh is a common phrase given with the call note few (or tew) during the day. It resembles the short catch notes of Ruby-crowned Kinglet and Cassin Virco.”
Three days later, on April 29, I awoke in the darkness at 4:20 a. m. to find a bluebird already singing. I wrote down his song thus: “Ic-ic IA, tAw, ic-ic, lAw, sc-ic towAg, towAe (often two-lAe, two-IAe: more musical), ic-ic, lAw, ic-ic lwode, towAe These songs, with minor variations, were given throughout the season. * * *
The singing of these birds resembled the usual song of the Western Robin even more closely than does the song of the Mountain Bluebird as observed in this locality. In the darkness I often found it difficult to tell whether a song was given by a Western Bluebird a few hundred feet away or by a Western Robin at a greater distance. To me the Western Bluebird’s singing, from a musical standpoint, is less enjoyable than that of its quieter relative, the song of the Mountain Bluebird being softer, more subdued, and more pleasingly modulated.
During the early part of the season, in April, while the Western Bluebirds were pairing and selecting houses, the males during the day frequently gave a double note that was not heard later in the season. This was a musical pe-wde, much resembling a goldfinch’s call. This was also coupled with the common call note to form a series of phrases which perhaps constituted a “mating song”; Pa-wAe, few few. Few few fa-wAe. Fc-wAe. Few few Je-wAe. Pe-wAe. Pa-wee, few, few . . . Another phrase sometimes given at this season I noted as etherick tee, the first double note resembling a common phrase of the Western Robin’s song.
Field marks: There are several partially or largely blue birds on the Pacific slope, but not one is so intensely blue as the male western bluebird; the rich blue of his head, wings, and tail and the deep chestnut on his breast are distinctive marks. The jays are all much larger, the blue grosbeak does not have the solidly chestnut breast and its stout bill is quite noticeable, and the lazuli bunting is a much lighter blue and has white wing bars. The colors of the female are similar to but much paler and duller than those of the male. The mountain bluebird, in its pale soft colors, is not likely to be confused with the western, as there is no chestnut in the plumage of either sex.
Fall: Theed Pearse writes to me that, on Vancouver Island, some birds, possibly local breeding individuals, move southward very early, during the last of June or the first two weeks in July. Other migrating parties pass though in August and as late as October 20, consisting of bluebirds, Audubon’s warblcrs, robins, and cedar waxwings. Mr. Rathbun tells me that the western bluebird is a very common migrant during the latter part of October in western Washington. Grinnell and Storer (1924) write:
The manner of association during the season of molt has not been observed, but by September flocks have been formed which include both adult and immature birds, and in this fashion they spend the winter. The flocks, in observed instances, included from 6 to 25 members. Sometimes other birds are associated. In Yosemite Valley we saw Western Bluebirds in company with Audubon Warblers on one or more occasions, and Mr. C. W. Michael (MS) reports Western and Mountain Bluebirds together there during November of 1920. Western Bluebirds and Robins are frequently seen together during the winter months though the two do not flock with each other in the usual sense of the word.”
They say that there is an up-mountain movement of the bluebirds in fall in the Yosemite region and that they are seen at high altitudes all through the late fall and early winter. “The attraction for these birds at these higher altitudes is the abundant supply of food in the form of mistletoe berries. This food supply, rather than weather, short of extremely severe storms, seems to be the factor regulating the stay of the bluebirds in the mountains. That snow alone is no particular deterrent to the birds’ stay is shown by our observations made on the stormy morning of December 10, 1914, at Mirror Lake, when bluebirds were flying about actively, now and again alighting on the snow-weighted mistletoe clumps. Masses of the snow would be dislodged and shower the observer beneath, but the birds themselves seemed in nowise discommoded.”
Mr. Cogswell writes to me: “This species is varyingly numerous in lowland areas from late in summer to early in spring but is usually abundant in the foothill areas around Pasadena and in the more open mountain canyons below snow level. Several were seen in Bear Valley, San Bernardino Mountains, on December 28, 1941, with a foot of snow on the ground. Together with their frequent companions, Audubon’s warbiers and house finches, they rove over the foothill mesas and into the outlying edges of town in small flocks (5 to 15), feeding on insects chiefly, but also at least occasionally on grapes and other berries.”
Mr. Rathbun tells me that in mild winters some of these bluebirds remain about his grounds off and on all winter, investigating his bird boxes, and begin their nest building early in spring.
SIALIA MEXICANA BAIRDI Ridgway
This handsome race of the Mexican bluebird breeds farther east than but not so far north as the western bluebird, according to the 1931 Check-list, “mainly in the Transition Zone from Utah, Colorado, and central western Texas south to Durango and Zacatecas. Winters from southern Utah and southern Colorado south to Sonora and Zacatecas.”
For a clear understanding of the characters separating the races of Sialia mezicana, as well as the individual variation within each of the subspecies, the reader is referred to an extensive paper on the subject by Robert Ridgway (1894). Later Ridgway (1907) described the chestnut-backed bluebird more concisely as: similar to S. m. occidentalis, but adult male with whole back and scapulars uniform chestnut, producing a large and conspicuous dorsal patch; cinnamon-rufous of under parts more extended, always extending broadly across chest, sometimes covering whole breast; adult female with upper parts browner than in S. m. occidentalis, the back and scapulars hair brown to between sepia and prouts brown, usually in strong and abrupt contrast with the mouse gray or hair brown of pileum and hindneck; young much darker and browner than those of S. m. occidentalis or S. m. anabeL~, with under parts more heavily streaked or squamated and the streaked areas more or less strongly suffused with pale fulvous or rusty brownish. Decidedly larger than S. m. occidentalis, with smaller bill.
There is, of course, intergradation ,vith the adjacent races and considerable individual variation in the distribution of the blue and chestnut areas.
Aiken and Warren (1914) write of its haunts and habits in El Paso County, Cob.:
While this species is common almost everywhere on migration, though probably never ranging quite as high as the next species, it breeds mainly in the yellow pine region between 7,000 and 8,000 feet, where it outnumbers the Mountain Bluebird. July 17. 1899, on the Divide north of Peyton, Aiken saw 20 Chestnutbacked to 5 of the Mountain Bluebirds, and it is probably more numerous On the Divide than anywhere else in the County. The two species are sometimes found in mixed flocks in the spring, especially when the weather is stormy. The appearance on the plains of this Bluebird during the spring migration is hut for a short time, as it goes into the mountains and onto the Divide by the first of April, but the storms which usually come early in May drive the birds down in small flocks which remain until the weather clears and the snow melts. At these times the birds often become much emaciated and some die from starvation, being unable to obtain food while the snow is on the ground.
Harry S. Swarth (1904) says of its haunts in the Huachuca Mountains, Ariz.:
During February and the early part of March I found the Chestnut-backed Bluebirds quite numerous in the lower foothills, and on the plains immediately near the mountains, being entirely absent from the higher parts of the range, where the snow still lay deep on the ground; but about the middle of March they began to move upward, and by the first of April there were none to be seen except in the higher pine regions, their hrceding grounds. Here they remained through the summer in the greatest abundance, none being seen below 8,000 feet, and being most numerous along the divide of the mountain. About the middle of August they began, to some extent, to move down to a lower altitude once more, for the evening of August 12th a small flock was seen flying overhead near the base of the mountains.
Russell K. Grater has sent me the following interesting note from Zion National Park, Utah: “This bird is a summer resident above 7,500 feet and is commonly seen in the open forest glades near meadows. Usually they range in groups of six or more before and after the nesting season. In winter they drift down from the highlands into the canyon bottoms but always prefer wide canyons with some open areas. Frequently they are found drifting through the pifion-pine: juniper forest, where they eat extensively of the fruit of the mistletoe. Some birds, when collected, had no other undigested food except the mistletoe. Nests have been found in hollow trees, usually about 7 to 15 feet from the ground. Eggs are laid in May and June and two broods are not infrequent. A nesting record of more than passing interest was recorded while I was living at Grand Canyon National Park. In May 1935 a hollow in an old pifion pine was utilized as a nesting site by both a chestnut-backed bluebird and a black-eared nuthatch. Both birds would occupy the hollow at the same time, sitting side by side. Each bird apparently fed only her own brood, and two families were raised by each set of parents during the summer. These birds were quite tame and were not at all disturbed when the hole into the hollow was enlarged sufficiently for a study of this unusual event. Careful records of the event were kept by more than one interested bird student at the park. This is the most unusual bird relationship thus far observed at Grand Canyon.”
The chestnut-backed bluebird nests also in old woodpecker holes and in bird boxes, lays from four to six eggs, and in all other respects does not differ materially from the western bluebird, which is treated more fully on the following pages. Dr. f~riedmann (1929) lists this bluebird as a very rare victim of the dwarf cowbird.
The measurements of 30 eggs average 21.5 by 15.9 millimeters; the eggs showing the four extremes measure 23.6 by 16.5, 23.4 by 16.8, 19.7 by 15.1, and 20.0 by 15.0 millimeters.
Range: Westcrn North America from southwestern Canada to central Mexico.
Breeding range: The bluebird of thc mexicana group breeds north to southern British Columbia (Beaver Creek. Vancouver Island, Alta Lake, 150 Mile flouse,Edgewood,and Newgate). East to southeastern British Columbia (Newgate); western Montana (Fortine, Columbia Falls, Lob, and Laurel); western Wyoming (Yellowstone Park and Pinedale); central Colorado (Estes Park, Golden, Colorado Springs, Wet Mountains, and Fort Garland); central New Mexico (Truchas Peak, Ribera, Capitan Mountains, and Clouderoft); western Texas (Guadalupe Mountains and Davis Mountains); southern Coahuila (Carncros); western Tamaulipas (Miquihuana); western Veracruz (Las Vigas and Cofre de Perote); and eastern Puebla (Tochimilco). South to Puebla (Tochimilco); Morelos (Huitzilac); and Michoac~n (Mount Tancitaro). West to western Michoac~n (Mount Tancitaro and Mount Patamban); southern Durango (El Salto); western Chihuahua (Colonia Garc!a); northern Sonora (San Luis Mountains); central northern Lower California (Sierra San Pedro Mjirtir, El Rayo, and 20 miles east of Ensenada); the Coast Range and sometimes the coast of California (San Diego, Los Angeles, Santa Barbara, Monterey, Nicasio, and Humboldt Bay); Oregon (Gold Beach, Elkton, Newport, and Olney); Washington (Aberdeen, the Olympic Mountains, and Mount Vernon); and southwestern British Columbia (Vancouver Island; Alberni and Beaver Creek).
Winter range: Through much of its range the species is resident or only retires to lower altitudes in winter. It winters north to southern British Columbia (Comox, Chilliwack, and the Okanagan Valley); to the valleys of the Cascades in Washington (Bellingham and Dungeness Spit, occasional at Spokane); Oregon (Portland, Salem, and Corvallis); eastern California (Lassen Peak region); western and southern Nevada (Carson City and Searchlight); Arizona (south rim of Grand Canyon, Salt River, and Tucson); central New Mexico (Socorro, Mbuquerque, and Las Vegas); and southwestern Texas (Frijoles, Marathon, and Fort Clark). In migration, possibly occasionally in winter, it has been found as far east as Kerrville, Tex. There is one record of occurrence in winter near Polson, Mont., near the south end of Flathead Lake.
The ranges as outlined are for the species as a whole, which has been divided into several subspecies or geographic races. The chestnutbacked bluebird (S. m. bairdi) breeds from Utah and Colorado south to Durango and Zacatecas; the western bluebird (S. m. occiden~alis) breeds from southern British Columbia and western Montana south to southern California; the San Pedro bluebird (S. m. anabelae) breeds in the Sierra San Pedro MArtir and the Sierra JuArez of northern Lower California.
Migration: Some early dates of spring arrival are: Colorado: Colorado Springs, March 4. Wyoming: Yellowstone Park, March 13. Montana: Fortine, March 9. Utah: Salt Lake City, March 6. Idaho: Rathdrum, March 3.
Some late dates of fall departure are: Idaho: Meridian, October 27. Utab: Kanab, October 21. Montana: Fortine, October 28. Wyoming: Yellowstone Park, September 8. Colorado: Beulah, October 24.
Egg dates: California: 104 records, April 4 to June 29; 58 records, May 2 to May 31, indicating the height of the season. Colorado: 9 records, May 6 to June 16.
Oregon: 29 records, April 18 to June 29; 15 records, Apr11 18 to May 21.
Lower California: 6 records, May 15 to June 12.
SAN PEDRO BLUEBIRD
SIALIA MEXICANA ANABELAE Anthony
It seems to be generally accepted now that this subspecies is confined in the breeding season to the Sierra San Pedro M~rtir and the Sierra Ju~rez in northern Lower California, though Ridgway (1907) mentions a number of bluebirds from upper California, as far north as Mount Lassen, that show more or less the characters of this form. For a critical study of the races of the Mexican bluebird, the reader is referred to an extensive paper on the subject by Ridgway (1894), in which some doubt was cast at first on the validity of this subspecies.
A. W. Anthony (1889) described this bird and named it for his wife, Anabel Anthony. He gave its subspecific characters as “differing from S. mezicana in slightly larger form, in the bay of the breast, which is divided by the blue of the throat, restricting it to patches on the sides of the breast, and in the almost entire absence of bay on the scapul~.” The female “differs from the females of S. mexicaruz in my collection in the more pronounced blue of the head and larger size.” He includes in its range Mount Lassen, Calif., Puget Sound, Utah, and Nevada; this extension of range is probably based on certain specimens from these localities that show some intermediate characters, such as those mentioned below by Ridgway.
Mr. Ridgway (1907) described the San Pedro bluebirds as “similar to S. m. mexicana, but with bill larger and stouter; blue of upper parts averaging less violaceous (more ultramarine), back more often mixed with chestnut laterally; adult female with back and scapulars grayish brown, forming a definite dorsal patch, distinctly defined against the brownish gray or dull grayish blue of pilcum and hind-. neck, and, with the grayish brown or brownish gray of throat, breast, etc., paler than in S. m. mexicana.” In a footnote he shows the variation in the color pattern in 43 adult males from the San Pedro M~rtir Mountains; 21 have no chestnut whatever on back or scapulars; 18 have the back chiefly blue; 4 have the back about equally blue and chestnut; 30 have the chestnut of the breast divided by the blue of the throat, a character of S. m. mexicana; 11 have the chestnut of the breast continuous anteriorly; and 2 do not belong to either category. This analysis shows that the characters of anabelae are not absolutely constant, even in its restricted range. In another footnote he says: “California specimens are not typical of this form, but are much nearer to it than to S. m. occidentalis, from which they differ in larger size, more restricted areas of chestnut (though this character varies greatly in both forms), and, on the average, decidedly richer or more violaceous hue of the blue.”
Since the Sierra San Pedro M~irtir has become the birthplace of so many local subspecies, it seems worth while to include here Mr. Anthony’s (1889) description of the region.
About one hundred and fifty miles south of the United States boundary, and midway between the Pacific Ocean and tbe Gulf of California, lies a high range of mountains, which is marked upon the later maps of the peninsula as “San Pedro Martir.” The region embraces a series of small ranges which rise from an elevated mesa, having a mean elevation of about 8,000 feet, and an extent of sixty by twenty miles. In these mountains are born the only streams that this part of the peninsula affords, and an abundance of pine timber is found throughout the region. Many of the ranges on the eastern side of the San Pedro Martir rise to an elevation of 11,000 feet, or even, in one or two places, to 12,500 (?) feet.
Arising as the region does from the dry, barren hills of the lower country to an elevation higher than any other on the peninsula or in Southern California, and presenting in its alpine vegetation and clear mountain streams features so different from the dry manzanita and sage-covered hills of the surrounding country, it is not unnatural to suppose that its animal life would be found to differ in some respects from that of the surrounding hills.
J. Stuart Rowley writes to me: “Near La Grulla in the Sierra San Pedro MArtir, of northern Lower California, I took a set of five slightly incubated eggs of this race of bluebird on June 12, 1933. So far as I can determine, the habits of this bluebird are no different from those of the western bluebird of the north.” Charles E. Doe, who now has this set in his collection at the University of Florida, in Gainesville, tells me that t.he nest was in a pine stub 8 feet. from the ground.
Eggs: The eggs of the San Pedro bluebird are probably indistinguishable from those of the species elsewhere. The measurements of 26 eggs average 20.9 by 16.2 millimeters; the eggs showing the four extremes measure 23.1 by 16.5, 20.2 by 16.9, 19.4 by 16.2, and 19.6 by 15.2 millimeters.