Throughout much of the western U.S. in spring and early summer, the Bullock’s Oriole can be found wherever large cottonwood or sycamore trees grow along streams. Bullock’s Orioles leave their breeding grounds rather early, typically by late July and August.
Baltimore and Bullock’s Orioles were once considered to be the same species, and in the Great Plains they do hybridize at times, but today they are considered to be distinct species. Bullock’s Orioles frequently return to the same general area to nest from one year to the nest.
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Description of the Bullock’s Oriole
The Bullock’s Oriole is sexually dimorphic, though both sexes have the somewhat long, bluish-black bill typical of orioles.
Males are brilliant orange on the face and underparts, with a black line through the eye and a black crown and upperparts, an orange tail tipped with black, and a very large white wing patch. Length: 9 in. Wingspan: 12 in.
Females are yellowish-orange on the head, have a grayish back, a white belly, and have two white wing bars instead of a large white patch.
Seasonal change in appearance
Juveniles resemble females. First spring males resemble females but have a black throat and a black line through the eye.
Bullock’s Orioles inhabit forest edges, streamside cottonwoods, and isolated groves of trees.
Bullock’s Orioles eat insects, berries, and nectar.
Bullock’s Orioles forage within trees and shrubs, sometimes visiting flowers or bird feeders for nectar.
Bullock’s Orioles breed throughout the western U.S. They winter in Mexico. The population has declined in recent decades.
Bent Life History
Visit the Bent Life History for extensive additional information on the Bullock’s Oriole.
The shape of a bird’s wing is often an indication of its habits and behavior. Fast flying birds have long, pointed wings. Soaring birds have long, broad wings. Different songbirds will have a slightly different wing shape. Some species look so much alike (Empidonax flycatchers) that scientists sometimes use the length of specific feathers to confirm a species’ identification.
- Male, Washington, June
- From below
- Male, immature, Washington, July
- From below
- Female, juvenile, Washington, Aug.
- From below
Wing images from the University of Puget Sound, Slater Museum of Natural History
Bullock’s Orioles hybridize with Baltimore Orioles in the Great Plains, where their ranges meet. They were formerly lumped as the Northern Oriole.
There are a number of records of vagrant Bullock’s Orioles in the eastern U.S., usually in the fall.
The song consists of a series of rich whistles. A short rattle call is given as well.
The male Hooded Oriole lacks black on the top of the head, has more extensive black on the throat and neck. The female Hooded Oriole is more lemon yellow than the Bullock’s female.
Baltimore Oriole males have an entirely black head and an orange patch in the wing along with a white wing bar. Female Baltimore Orioles have a whitish throat and a darker back than female Bullock’s Orioles.
The Bullock’s Oriole’s nest is a deep, hanging pouch of plant fibers, grass, and string and is lined with finer materials. It is placed near the end of a deciduous tree branch.
Number: Usually lay 4-5.
Color: Pale bluish in color with darker markings.
Incubation and fledging:
The young hatch at about 11-14 days, and fledge at about 14 days, though remaining dependent on the adults for some time.
Bent Life History of the Bullock’s Oriole
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 Bullock’s Oriole – the common name and sub-species reflect the nomenclature in use at the time the description was written.
ICTERUS BULLOCKII BULLOCKII (Swainson)
This highly colored oriole replaces the Baltimore oriole in the western half of North America, except for a narrow strip along the Pacific coast from the San Francisco Bay region to northern Baja California. Its breeding range extends from the southern parts of British Columbia, Alberta, and Saskatchewan to southern Texas and northern Mexico, and from the western edge of the Great Plains and prairie regions to the Pacific slope. At the eastern border of its range, where it meets that of the Baltimore oriole, these two closely related species appear to interbreed, producing an interesting series of apparent hybrids, to be referred to later .
The favorite haunts of Bullock’s oriole are in the growths of deciduous trees, cottonwoods, willows, sycamores, etc., that line the streams or irrigation ditches in open country, in the prairie regions, and in cultivated lands. The presence of water is not essential, for they are equally at home in some of the partially dry washes that extend down into the grasslands from the mountain canyons, where there is some underground moisture, or far from any water in the tree-claims about the ranches; they are also found living and nesting in the semiarid mesquite groves in Arizona. It is, perhaps, less intimately associated with human habitations than is the more sociable Baltimore oriole, though it does nest to some extent in villages and near houses, especially about farms and ranches.
Nesting: Bendire (1895) describes this very well as follows:
The nest resembles that of the Baltimore Oriole, but as a rule it is not quite as pensile, and many be more or less securely fastened by the sides as well as by the rim to some of the adjoining twigs. The general make-up is similar. As many sections where Bullock’s Oriole breeds are still rather sparsely settled, less twine and such other material as may be picked up about human habitations enter into its composition. Shreds of wild flax and other fiber-bearing plants and the inner bark of the juniper and willow are more extensively utilized; these with horsehair and the down of plants, wool, and fine moss, furnish the inner lining of the nests. According to my observations, the birch, alder, cottonwood, eucalyptus, willow, sycamore, oak, pine, and juniper furnish the favorite nesting sites; and in southern Arizona and western Texas it builds frequently in bunches of mistletoe growing on cottonwood and mesquite trees.
The nests are usually placed in low situations, from 6 to 15 feet from the ground, but occasionally one is found fully 50 feet up. A very handsome nest, now before me, * * * is placed among six twigs of mistletoe, several of these being incorporated in the sides of the nest, which is woven entirely of horsehair and white cotton thread, making a very pretty combination. The bottom of the nest is lined with wool. Outwardly it is 6 inches deep; inside 4~ inches. The entrance, at the top, is oval in shape, somewhat contracted, and 4 by 2~ inches wide. Another peculiar specimen before me, taken near Ureka, California, May 29, 1860, is woven among and fastened to a bunch of needles of the longleaf pine; this nest resembles an inverted cone, and is quite unique in structure. I have also seen double nests, one placed beside and fastened to one previously built that had for some unknown reason been abandoned.
In the vicinity of Fort Lapwai, Idaho, it was especially abundant, and, although suitable nesting sites were by no means scarce, I have seen three occupied nests of this Oriole in a small birch tree close to a nest of the Arkansas Flycatcher, showing them to be very sociable birds. Near Camp Harney, Oregon, a Swainson’s Hawk, an Arkansas Flycatcher, and a pair of this species nested in the same tree, a good-sized pine. A. K. Fisher tells me that he saw hundreds of these nests in a large row of cottonwoods, east of Phoenix, Arizona, in June, 1892.
In Arizona, Herbert Brandt (MS.) found this oriole often nesting close to an occupied nest of the western kingbird, in the mesquite chaparral. “At one place in a sycamore I saw them nesting within three feet of each other, and they could have used, if they wished, opposite sides of the tree, 30 feet apart. Twice they resided in the same small mesquite.” In Texas, he noted a similar association between Bullock’s oriole and the scissor-tailed flycatcher.
Near the Huachuca Mountains, Ariz., we took a set of eggs of this oriole, about 10 feet up in a sycamore, and a set of eggs of the western flycatcher, about 20 feet from the ground in the same tree.
On May 24, 1923, near Brownsville, Tex., I collected a set of five fresh eggs from a typical nest of Bullock’s oriole about 15 feet up in a large mesquite; R. D. Camp told me that this species does not breed there, but, after watching for a long time, I plainly saw both birds go to the nest It is evidently not a common breeding bird there.
C. S. Sharp (1903) has published an interesting paper, illustrated with photographs, describing three distinct types of Bullocks’ orioles’ nests, one of which is wholly pensile, one semipensile, and one not at all pensile; his description of an especially beautiful pensile nest follows:
The twigs to which it was attached formed a fork, and a few inches above, another small twig extended downward in the same direction. The nest was wholly suspended from these, the twigs, with some of the leaves attached being worked into it for a little distance down the sides and back. With these exceptions and two or three long horse hairs it was composed wholly of wild oats and rather loosely woven. A few of the oat heads show on the inside where they were worked into the nest itself, but almost all are on the outside, the long stems being worked in to their heads which stood out in a beautiful and graceful fringe all around and below for from one to three inches or more. The effect was striking and unusual. * * * The dimensions in inches are as follows: Depth outside (extreme) 14; depth outside (front) to opening, 8; depth inside to opening 5}4; diameter outside, 7; diameter inside, 4; circumference 21 .
J. F. Illingworth (1901) writes:
Until the season of ’97 I have never known the Bullock’s Oriole to use palmfiber in the construction of its home, but I found a nest May 11, 1897, in a peach tree, composed entirely of this fiber. It was well lined with chicken feathers and placed between several small branches. A pair of Bullock’s Orioles built a nest this year in an almond tree near the porch, and I had an excellent opportunity to watch them while they were at work. The place chosen was in a wide fork between four small branches. Both birds worked on the nest and as soon as they had loosely formed the walls or framework, one of them worked inside and the other outside. The latter would bring a horse-hair or a piece of twine in its beak and pass the end through the wall of the nest to his mate inside who took the end and passed it out again through another place. In this way the nest was soon woven quite smooth and looked as if it had been made with a darning needle by hand.
Eggs: Bullock’s oriole lays from three to six eggs to a set; four and five are the commonest numbers, but sets of six are not rare. Bendire (1895) describes them as follows:
The eggs are mostly elongate ovate in shape, a few are ovate, and an occasional set is almost wedge-shaped or cuneiform. The shell is close grained and only slightly glossy. The ground color is generally of the same subtle grayish-white tint as that seen in the eggs of the Baltimore Oriole, but the proportion of the pale bluish white eggs is greater than with the latter. Occasionally the ground color is pale vinaceous buff. The markings are similar in color to those found on the eggs of the preceding species [Baltimore oriole], but as a rule they are not so coarse, and the fine hair lines running in irregular tracings around the larger axis of the egg are more prevalent; they are also a trifle larger .
The average measurement of 144 specimens in the United States National Museum collection is 23.80 by 15.93 millimetres, or about 0.94 by 0.63 inch. The largest egg in the series measures 25.40 by 16.76 millimetres, or 1 by 0.66 inch; the smallest, 21.34 by 15.24 millimetres, or 0.84 by 0.60 inch .
Young: Bendire (1895) states: “Only one brood is raised in a season, and the duties of incubation, which are performed almost exclusively by the female, last about 14 days. I have often watched the sitting bird, and have never seen the male on the nest.”
Mrs. Wheelock’s (1904) observations confirm this statement; and she adds:
Her mate is always within calling distance, keeping a vigilant watch for squirrels, crows, and jays; and should any of these enemies appear, not only he but the mother bird, joined by all the orioles and blackbirds within hearing, will fly at the intruder and effectually banish him from the vicinity. When newly hatched, the young orioles are naked, pink babies with little tufts of thin white down on head and back. For nearly a week after they are feathered the down waves rakishly on either side of the crown and about the shoulders, gradually wearing off as they brush about through the bushes.
Like all oriole babies, these demand the constant attention of both parents, crying loudly for more the moment their mouths are emptied of the last mouthful, not in the least trying to help themselves, but following the adults about for a week or two after leaving the nest. * * * I believe the families usually keep together until late in August, when the males join flocks of their own sex for the September migration southward.
Plumages: The natal down of Bullock’s oriole is white, long, and rather scanty. The sexes be practically alike in the juvenal plumage, though the female is usually rather paler; this plumage closely resembles that of the adult female, grayish olive above with yellowish olive tail and wing coverts and dull bully whitish below; but there is no black on the throat or wings, and no orange on the head and neck. A postjuvenal molt occurs in late summer, involving the contour plumage and the wing coverts but not the rest of the wings nor the tail; this produces the first winter plumage, in which the young male acquires black lores and a narrowly black throat, but which is otherwise like the plumage of the adult female; young birds may breed in this plumage. At the first complete postnuptial molt, the following summer, the adult winter plumage is acquired; this is like the adult spring plumage, but in the male the feathers of the back and under parts are margined with gray. Adults have a complete postnuptial molt in summer, but apparently no spring molt, the spring plumage being acquired by wear.
At my request, James L. Peters examined the large series of Bullock’s orioles in the Museum of Comparative Zoology and has sent me his report, from which I gather the following additional information: The postjuvenal molt begins about the middle of August and is completed by about the middle of September. The amount of black acquired in the throat and lores at this molt seems to vary considerably and the time at which it is acquired also varies. Two males, taken September 16 and October 10, both lack it; two males, taken October 7 and 11, have whitish lores and throat patches of scattered black feathers; but a male, taken October 6, has fully developed black lores and throat patch. He says that the first prenuptial molt of the male varies greatly; “in some individuals new black feathers with olive edges appear on the crown; sometimes only half a dozen such are to be found; in others the crown is entirely covered; the first traces may appear by the end of January. Some individuals acquire new scapulars and interseapulars between the end of January and the end of March, but not over half of those examined did so.”
The sequence of molts in the female is similar to that of the male. There is considerable individual variation in the amount of black acquired on the throat at the first prenuptial molt; out of 27 young females examined by Peters, 14 did not acquire it at all, 10 acquired only traces, and only 3 had the black stripe complete.
Food: F. E. L. Beal (1910) examined the contents of 162 stomachs of Bullock’s oriole, taken in every month from April to August, inclusive. The contents consisted of 79 percent animal matter and 21 percent vegetable:
The animal food consisted mainly of insects, with a few spiders, a lizard, a mollusk shell, and eggshells. Beetles amounted to 35 percent, and all except a few ladybugs (Coccinellidae) were harmful species. The coccinellids were found in 9 stomachs, but the percentage was insignificant. Many of the beetles were weevils, and quite a number belonged to the genus Balaninus, which lives upon acorns and other nuts. Ants were found in 19 stomachs, and 1 contained nothing else. Hymenoptera other than ants were found in 56 stomachs, and entirely filled 2 of them. Including the ants, they amount to nearly 15 percent of the food of the season.* * *
One of the most interesting articles of food in the oriole’s dietary is the black olive scale (Saisactia oteae). This was found in 45 stomacbs, and amounted to 5 percent of the food. In one stomach these scales formed 87 percent of the contents; in another, 82; and in each of two others, 81 percent. * * * Hemiptera other than scales are eaten quite regularly. They amount to a little more than 5 percent of the food. * * * They were mostly stinkbugs, leafhoppers, and tree hoppers. Plant lice (Aphididac) were found in one stomach.
Lepidoptera, moths, pupae, and caterpillars, are the largest item in the food, amounting to 63 percent in April, only 8 percent in July, and averaging a little more than 41 percent for the season. He continues:
Perhaps the most interesting point in connection with the Lepidoptera is the eating of the pupae and larvae of the codling moth (Carpocapsa pomonetla). These were found in 23 stomachs, which shows that they are not an unusual article of diet. No less than 14 of the pupa cases were found in one stomach, and as they are very fragile, many others may have been present, but broken up beyond recognition. It is curious that the oriole should find these insects. During the greater part of their larval life they are concealed within the apple. When ready to pupate they crawl out and at once seek some place of concealment, such as a crevice in bark or among clods or rubbish, where they can undergo their changes. To find them, therefore, birds must hunt for them.
Grasshoppers amounted to a little more than 3 percent for the season, but “2 stomachs, both taken in June, contained nothing else, and another had 97 percent of them. * * * Practically all of the vegetable food consists of fruit, which amounts to a little more than 9 percent. * * * J~ was found in 67 stomachs, of which 16 contained cherries; 11, figs; 5, blackberries or raspberries; 1, elder-berries; and 34, fruit pulp not further identified. One stomach was entirely filled with the pulp and seeds of figs.” Fruit amounted to nearly 40 percent in July.
Herbert Brandt (MS.) watched a Bullock’s oriole feeding for several mornings at the blossoms of bird of paradise shrubs in Arizona. “The oriole came just at dawn. He would fly from flower to flower, often within a few inches of my face, and I could see distinctly by his throat actions that he was drinking the nectar therefrom. Never did he show indications of picking out insect life from the deep tubes. All the time he was feeding, which was usually long enough for a visit to each flower, he kept talking to himself, uttering a musical peep note. Later in the day either this oriole or another of the same kind would search the crimson flowers of the ocotillos on the other side of the house in the same manner, but I never saw the oriole among the Bird of Paradise plants at any other time than its regular dawn visits. Evidently this exotic plant does not produce nectar in its cups during daytime.”
W. Otto Emerson (1904) observed these orioles feeding on honey in the blossoms of the eucalyptus trees; one that he shot had its crop so full of the honey that it oozed out of its mouth when he picked it up. IRidgway (1877) noticed that, in Nevada, in May, “they were then subsisting chiefly on the tender buds of the greese-wood,” as were some other birds. Bullock’s orioles also feed to some extent on apricots, persimmons, hawthorn berries, and probably many other wild fruits and berries.
Claude T. Barnes writes to me from Utah: “For half an hour I stood beneath an elm tree observing a pair of Bullock orioles. Some of the leaves were so infected with lice that they were curled edge to edge, and each oriole was busy working its bill into leaf after leaf. When standing on a branch without eating, each bird uttered a chup every second or so.”
These orioles are helpful in destroying the cotton boll weevil. A. H. Howell (1907) writes: “These orioles are rather abundant in the regions they inhabit, and in August and September visit the cotton fields in flocks of 10 to 20 individuals. About 27 percent of those examined contained boll weevils, the largest number of weevils found in one stomach being 41. The total number of weevils eaten by 40 birds was 133, an average of over 3 weevils to each bird.”
They do good work on the alfalfa weevil, also. E. R. Kaimbach (1914) says: “Although the alfalfa weevil in all its stages is found most frequently on or near the ground, it was present in each of seven stomachs collected. Two birds taken in June had fed on it to the extent of 8~ percent of their food, while in the following month it formed nearly twice that amount. One bird collected in July had eaten no less than 21 adults, equaling 30 percent of its food. No larvae were taken by these birds even though this form of the insect was in great abundance, so that the adults may have been captured either on the wing or upon branches of trees which had intercepted their flight.”
That these orioles can catch insects on the wing is shown by the following observation by J. G. Tyler (1913): “The small yellow butterfly that is found in such numbers in alfalfa fields at certain seasons seems to be especially attractive to the orioles, and countless dozens of them are devoured. I have seen this bird in the role of flycatcher at such times, flying from a fence wire and seizing a butterfly on the wing, a rather clumsy effort but serving the purpose.”
Economic Status: From the above account of its feeding habits we must conclude that, although Bullock’s oriole unquestionably does some damage to cultivated fruits and berries, it more than pays for this by the large number of harmful insects that it destroys, an action that is of real benefit to the agriculturalist. For this reason, and because the beauty of its gorgeous plumage and its charming song bring so much joy to so many people, it should be rigidly protected and encouraged to live and breed about our farms, ranches, and gardens.
Behavior: As mentioned above, Bullock’s orioles are most devoted parents and staunch defenders of their nests, eggs, and young. Clarence Cottage (MS.) sends me his observations of the bird in southeastern Utah: “In this locality the orioles were quite numerous and were in the midst of their nesting season. Magpies (Pica pica Hudson) also were very common. One of these omnivorous feeders, a juvenile about one-half to two thirds grown, was observed circling about an oriole’s nest as though searching for a breakfast of eggs. The magpie soon alighted in the tree in which the nest was hanging and began to come closer and closer to the beautiful swinging structure. Almost at the instant the magpie settled upon the edge of the nest, the male oriole, which apparently was but a few rods away, was beard to give an abrupt and angry call of warning. A moment later the enraged male came with all his force at the intruder, striking it on the crown of the head. The magpie dropped to the ground, stunned to such an extent that I was able to pick it up, and only after 10 minutes could it regain sufficient strength to fly away. W. L. Finely (1907) made some observations on a pair of these orioles that nested near his house, saying:
I never saw birds more in love than the orioles were. We watched them from the time they were first mated. They were always together in the trees about the orchard. * * * Just at the side of the house were three large cherry trees with wide-spreading branches almost to the windows. When the dark shades were drawn the windows made a very good mirror. One day when the pair of orioles were playing about the cherry trees I saw the female light on a low branch in front of the window. Then in a few moments she flew down and lit on the sash. The next day I saw both the orioles at the window. The male sat near on the branches and the female on the sill. As I watched she fluttered up against the window, trying her best to hang on, till she slipped down to the bottom. Then she turned her head and watched in the glass. The more she looked the more excited she seemed to get, and she fluttered against the glass till out of breath. Then the mate flew down beside her. Time after time the birds were seen at the window.
Once a strange male oriole alighted in the nesting tree, but “the new arrival had hardly lit when there was a flash of color, and the father of the nestlings darted at the intruder like a little fury. Through the branches, under trees, over the barn, and across the orchard the righteous pursuer and the invidious pursued darted.”
On another occasion, “a newly mated pair of orioles were living about a grove of trees, and the male bird was in such fine plumage that a collector shot him for his cabinet. The next day the female appeared with a new husband, who was as bright and fine looking as the bird she lost the day before. At the first chance this male was also shot, partly, it was said, because he was such a fine bird and partly to see if the female would find another as readily. Two days later she appeared with a third husband, who went the way of the two former ones. The female then disappeared for a few days, but returned again with a fourth suitor. These two began building in a eucalyptus tree and soon had a family of young birds.”
This incident clearly illustrates the well-known fact that the urge for reproduction is very strong in birds, also that they do not grieve long over the loss of a mate, and that there are always enough unmated birds to fill in a gap caused by accident. Though this may have been an extreme case, such happenings are very common.
A. W. Anthony (1921) tells of the strange behavior of a captive Bullock’s oriole that had never shown any fear of human beings, but showed “absolute terror” whenever its mistrcss appeared in a new dress adorned with a string of dark beads; after the beads were removed, the behavior of the bird became normal.
Voice: Dawson (1923) writes: “The Bullock Oriole is either musical or noisy, but oftener both together. Both sexes indulge a stirring rattle which seems to express nearly every variety of emotion. Upon this the male grafts a musical outcry, so that the whole approaches song. A purer song phrase more rarely indulged in may be syllabized as follows: Cut cut cudut whee up chooup. The last note comes sharp and clear, or, as often, trails off into an indistinguishable jumble. The questing note, or single call, of the male is one of the sweetest sounds of springtime, but an even more domestic sound, chirp trap, uttered while he is trailing about after his swinking spouse, appears ridiculously prosaic.”
Grinnell and Storer (1924) describe the song of the male as a “slightly varying series of syllables, rhythmically accented, like hi~5kip-y-ty-ho~-hoy, but with a peculiar quality impossible to describe (fide senior author); also a mildly harsh cho,.cha-cha-cha, etc., in rapid sequence, and a single clear note, kleek. Female and young give simple harsh blackbird-like notes.”
Ralph Hoffmann (1927) says: “In late March or early April a flash of orange or black in the delicate green of cottonwoods, a characteristic chatter, or the kip, kit-tick, kit-tick, whew, wheet of the song announce the arrival in southern California of the Bullock Oriole.”
Mrs. Wheelock (1904) writes: “Its call-notes and song resemble those of the Baltimore, but have less sweetness and variety. ‘Where the latter whistles half a dozen variations on his original theme of five notes, the Bullock is content to repeat the same phrase with few modifications. Nor have I ever heard him give the love song that is poured out by the Baltimore with such tenderness just at dawn when his mate is on the nest.”
Field Marks: A brilliant pattern of orange, black and white marks the adult male Bullock’s oriole. The top of the head, hind neck, upper back, central tail feathers, and tip of the tail are black; the lores, a narrow stripe behind the eye, and the throat are also black. The wing coverts and edges of the secondaries are white. The rest of the plumage, including the forehead, a broad band above the eye, sides of the head and neck, and entire under parts are rich, brilliant orange; the rump, upper tail coverts, and the lateral tail feathers are also orange. The female is much more soberly colored, olive above and bully white below, but the sides of the head and neck are more tinged with orange than in other orioles, there is a dusky streak through the eye, some black on the throat, and two white wing bars.
Enemies: The usual enemies of small birds: crows, magpies, jays and squirrels: often attempt to rob the nests of eggs or young; the nests are often more accessible than are those of the Baltimore oriole, but the parents are good guardians and often succeed in driving the robbers away.
Friedmann (1929) records the Bullock’s oriole as a rather rare victim of the dwarf cowbird, but says that this “species is frequently parasitized by the Red-eyed Cowbird.” Major Bendire (1895) says; “Bullock’s Oriole may occasionally rid herself of the parasitic egg; at any rate I noticed the remains of one lying under a nest of this species, with portions of one of her own. This nest contained only three eggs of the rightful owner, and the bird was sitting on these.”
Fall: Referring to the Fresno district of California, J. G. Tyler (1913) writes: “The great majority of our orioles depart about the twentieth of July, or at the close of the nesting season. No doubt a scarcity of food during the hot, dry months ~f August and September is responsible for the short stay of these birds. Probably they scatter out and range up into the higher hills, as many summer residents do in the southern part of the state. This species has been noted in small numbers along the San Joaquin River during August.”
The fall migration in Arizona is referred to by Swarth (1904) as follows: “The only time at which I have seen Bullock Orioles at all abundant in the Iluachuca Mountains was in August 1902. About the middle of the month flocks of from ten to twenty, nearly all young birds, could be seen along the canyons up to an altitude of about 5,500 feet. Most of these must have come in from other parts of the country, for I have never found them breeding at all abundantly in the mountains, being in fact, the rarest of the three species of orioles occurring there.”
Range: Southwestern Canada to Costa Rica .
Breeding Range: Bullock’s oriole breeds from southern British Columbia east of the coastal ranges (Milner, Alkali Lake, Okanagan Landing), northwestern Montana (Flathead Lake) southern Alberta (Warner, Medicine Hat), southwestern Saskatchewan (Maple Creek, Eastend), northeastern Montana (Fairview), southwestern North Dakota (Medora), western South Dakota (Harding County, Black Hills), western Nebraska (Chadron, McCook), western Kansas (Garden City), western Oklahoma (Gate), and central Texas (Vernon, Austin) ; south to central and southern interior California (Mount Saint Helena, Twentynine Palms), southern Nevada (Charleston Mountains, Pioche), southwestern Utah (Saint George), central and central-western Arizona (Prescott, Tucson), northeastern Sonora (Sane, Pilares), probably northern Chihuahua (Casas Grandes), central Coahuila (Monclava), and southern Texas (Rio Grande City, Brownsville). Summer records to east of this Range: North Dakota (Towner), South Dakota (Pierre), Kansas (Fort Riley, Manhattan, Lawrence). Hybridizes extensively with I. galbula in western Oklahoma and western Nebraska.
Winter Range: Winters from southern Sinaloa (Mazathin), Mexico. (Tlalpam), and Puebla south, west of the continental divide, to northwestern Costa Rica (Liberia); casually north to central California (Durham, Drytown) and southern Texas (Nueces), and southern Louisiana (Cameron, Baton Rouge).
Casual records: Casual in western Washington (Tacoma, Vancouver).
Accidental in New York (Onondaga County), Massachusetts (Falmouth), Maine (Sorrento), and Georgia (Grady County).
Migration: The data deal with the species as a whole.
Early dates of spring arrival are: Sonora: Tesia, March 19. Texas: Rockport, March 20; Cameron County, April 4. Oklahoma:
Cimarron County, May 2. Nebraska: Albion, May 7. South Dakota: Rapid City, May 21. Manitoba: Brandon, May 24. Saskatchewan: Eastend, May 26. New Mexico: Carlisle, April 14. Arizona: Santa Catalina Mountains, March 18. Colorado: Grand Junction, April 25. Utah: Saint George, April 30. Wyoming: Cheyenne, April 30 (average of 15 years for Wyoming, May 12). Idaho: Meridian, April 30. Montana: Kirby, May 8; Custer County, average, May 20. Alberta: Warner, May 15. Calfiornia: San Diego, March 1; Escondido, March 5. Nevada: Pioche, April 23. Oregon: Josephine County, April 13. Washington: Yakima, April 22. British Columbia: Okanagan Landing, May 6.
Late date of spring departure: Sonora: Guirocoba, May 12.
Early dates of fall arrival are: Guerrero: Chilpancingo, October 7. Guatemala: Finca Carolina, October 20. Costa Rica: Liberia, November 1.
Late dates of fall departure are: British Columbia: Okanagan Landing, August 29. Washington: southeastern Washington, September 8. Oregon: Klamath County, September 10. Nevada: Lee Cafion, August 25. California: Hayward, November 16; Buena Park, September 21. Alberta: Red Deer River, August 29. Montana: Huntley, September 11. Idaho: Pocatello, September 5. Wyoming: Laramie, September 16. Utah: Saint George, November 27. Colorado: Pueblo, October 24; Boulder County, September 30. Arizona: Tombstone, September 28. New Mexico: Mesilla, October 2. Saskatchewan: Eastend, August 11. Manitoba: Brandon, August 15. South Dakota: White River, August 29. Oklahoma: Cimarron, September 14. Texas: Brownsvifle, November 6; Victoria, October 20.
Egg dates: California: 160 records, April 22 to June 11; 82 records, May 11 to May 25.
Texas: 22 records, April 30 to June 25; 12 records, May 15 to May 29.
Utah: 10 records, May 27 to June 17; 5 records, June 4 to June 7.
Lesser Bullock’s Oriole
ICEERUS BULLOCKII PARVUS van Rossem
Based on the study of a series of 42 adult males and 15 adult females referable to this race, van Rossem (1945) named this subspecies and described it as “similar in color to Icterus bullockii bullockii (Swainson) of western North America in general. Size distinctly smaller. Measurements of the type are: wing, 97; tail, 76; culmen, 18.4; tarsus 23.2; middle toe, minus claw, 16.7. The corresponding measurements of Swainson’s type of Xanthornus bullockii (examined at Cambridge, England, in 1933, and again on July 4,1938) are 105, 83, 20.0, 24.5, and 17.8 mm. Range: Coastal slope of California from the San Francisco Bay region south to northern Baja California, and eastward in the extreme southern part of the range to the lower Colorado River valley. Winter range undetermined but occurs in southeastern Arizona and southern Sonora in migration.”
It is of interest to note that Ridgway (1902), in a footnote, called attention long ago to the fact that orioles of this species from California, west of the Sierra Nevada, are smaller than those from the interior to the eastward of that range .
The observations made by Alden H. Miller (1931) on the song and territorial behavior of two pairs of Bullock’s orioles in Contra Costa County, Calif., probably apply to birds of this subspecies. He says that: The male Bullock’s Oriole arrives on the breeding ground before the female and establishes a singing post, perhaps the entire territory. The females arrive one or two weeks later and come to occupy a territory jointly with a male. The female shares in the defense of territory. * * * The male and female of a pair do not cooperate completely in the defense of territory at least at a time before the nest is built. That is, a female during this period possesses an urge to defend a territory to the exclusion of other females, the male to the exclusion of other males. Other males during or preceding nest building are not repulsed from the territory by the female but instead may be acceptable to the female and may be courted. The converse doubtless is true of the male at other periods in the breeding season. Certainly the male before nest construction is tolerant of two females within his territory. At the beginning of nest construction the females pursue and beg from the males, posturing, fluttering the wings, and singing. At this time the males appear to be passive and consistently move away from the advances of the females. Nevertheless, in flight the males may follow after the females.
He demonstrated clearly that the females sing more or less regularly during the early part of the nesting period, and gives a chart showing the difference in the songs of the two sexes .
The utterances of female Bullock’s Orioles while in defense of territory and in association with males in every way are comparable to the songs of males and may be considered as true territorial songs. The song of the female is similar to that of the male in rhythm, pitch, and quality except as regards the concluding notes of the song which in the female are slightly harsher in quality, range over lesser intervals of pitch and show important modifications of the rhythm as compared with those of the male. Before or during nest building the songs of females on occasion may be even more abundant than the songs of the males * * * The songs of the two females were not identical. * * * The songs of the two males always were extremely similar one to the other. The females sang repeatedly from the ground whereas the males with one or two exceptions sang only while in the trees. The females sang in the trees near their respective males.
Range: Galifornia and Nevada to northwestern Mexico.
Breeding Range: The lesser Bullock’s oriole breeds from centralwestern and southern California (Santa Rosa, San Jacinto Mountains), southern Nevada (opposite Mohave, Arizona) and central-western Arizona (Colorado River Valley); south to northern Baja California (San Rafael, Colorado Delta) and northwestern Sonora (Colonia, San Luis).
Winter Range: Winter range largely unknown; possibly sparingly in southern California (Los Angeles) and Arizona (Parker), probably in central-western Mexico, south to Guerrero (Chilpancingo) ; migrants taken in Sonora (San Javier, Tesia, Guirocoba), and Arizona (north to Camp Verde, rarely to Wupatki National Monument).