The common and widespread Bullock's Oriole (Icterus bullockii) breeds in western North America from southern Canada south to northern Mexico. It winters mainly from Mexico south to Guatemala, with small numbers found along the Gulf coast of the southeastern United States from Texas to southern Georgia and Florida. It is found in summer along forest edges and in isolated groves and streamside woods, especially in cottonwood trees. Its habits appear to be similar to those of the Baltmore Oriole (Icterus galbula).
As a result of frequent hybridization between the Bullock's and Baltimore Orioles where their ranges meet in the Great Plains, these two orioles were at one time treated as conspecific (i.e., members of the same species), representing two forms of a species that was known as the Northern Oriole. However, genetic studies have indicated that these two species are not even each other’s closest relatives (for a full discussion of this issue, see Jacobsen and Omland 2011).
(Kaufman 1996; AOU 1998)
Bullock’s orioles (Icterus bullockii) are native to western North America, especially most of the western United States. They are common throughout most of their range (Jaramillo and Burke 1999). They are found as far north as southern British Columbia during the breeding season, (Jaramillo and Burke 1999; Rising and Williams 1999) but the winter range is largely confined to Mexico (Jaramillo and Burke 1999; Howell and Webb 1995). Though no geographic boundary hinders movement to the east, the range generally ends in the western counties of North Dakota, South Dakota, Kansas, and in central Texas (Jaramillo and Burke 1999; Rising and Williams 1999). The breeding range extends into southern Canada, including Vancouver Island, British Columbia, Alberta, and Saskatchewan (Jaramillo and Burke 1999; Rising and Williams 1999). Bullock’s orioles also breed in Durango, Sonora, and Baja states of northern Mexico (Howell and Webb 1995; Jaramillo and Burke 1999). Bullock’s orioles are absent from southwestern Arizona and high elevation, arid portions of Idaho (Rising and Williams 1999). During winter, Bullock’s orioles may be found throughout Mexico, from Sinaloa south and east through central Mexico to Oaxaca. They are occasionally seen during the winter months in Baja California and in Guatemala (Howell and Webb 1995; Jaramillo and Burke 1999; Rising and Williams 1999).
Biogeographic Regions: nearctic (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Breeding
Regularity: Regularly occurring
Type of Residency: Breeding
Global Range: BREEDS: southern interior British Columbia, southern Alberta, southwestern Saskatchewan, eastern Montana, southwestern North Dakota, and central South Dakota south (east of coastal areas of Washington and Oregon) to northern Baja California, central Sonora, northern Durango, Coahuila, and central and southern Texas, and east to western Nebraska, western Kansas, and western Oklahoma (AOU 1983). WINTERS: regularly in coastal California, and from southern Sinaloa, the state of Mexico, and Puebla south to Guatemala (casually to northwestern Coasta Rica), in small numbers in the Gulf coast region from Texas to southern Georgia and Florida, and casually north to central California and southern Arizona (AOU 1983). MIGRATES: regularly through western North America west of the Rockies, including Baja California (AOU 1983).
Bullock’s orioles are medium-sized orange orioles. This species is sexually dimorphic, with males being slightly larger than females. Males range in length from 17.2 to 19.3 centimeters, while females are from 16.8 to 19.1 centimeters. Bullock’s orioles range in mass from 29 to 43 grams (Rising and Williams 1999). The culmen is straight and mostly black; the lower edge of the culmen is blue (Jaramillo and Burke 1999; Sibley 2000). In adults of this species, the lower mandible is bluish gray. All exposed skin is bluish gray (Jaramillo and Burke 1999). In adults, the tail is square and slightly graduated (Sibley 2000).
During the breeding season, adult males are characterized by their strongly contrasting black and orange plumage and black throat patch, though older females may also display a small throat patch. Though the crown is black, the rest of the head is orange, with a black eye-line that extends to the crown (Jaramillo and Burke 1999; Rising and Williams 1999; Sibley 2000). The supercilium is bright orange. The underparts and breast range in color from yellow to orange while the back is black (Jaramillo and Burke 1999; Pyle and Howell 1997; Rising and Williams 1999; Sibley 2000). Although the tail is mostly black, the outer three or four retrices are tipped orange, forming a dark T shape beginning at the base of the tail (Jaramillo and Burke 1999; Sibley 2000). The wing coverts are edged in white, forming a wing panel. The scapulars are black (Jaramillo and Burke 1999; Rising and Williams 1999).
Adult females are duller and, in most cases, lack the dark throat patch seen in male Bullock’s orioles (Jaramillo and Burke 1999; Pyle and Howell 1997). The upperparts, face, and breast are a dull grayish yellow with indistinct dark streaks on the back. The underparts are grayish, ranging in color from white to yellow (Jaramillo and Burke 1999; Rising and Williams 1999; Sibley 2000). The coverts are fringed white, and do not form a solid wing-panel as in the male, while the secondaries and tertials are fringed gray. The crown is olive. Alternatively, adult females may have a small black throat patch, though they lack the black lores seen in adult males. It is hypothesized that females with throat patches are older individuals (Jaramillo and Burke 1999).
Immature males resemble adult females, though in adult females the wings show less abrasion. Immature females are similar to juveniles of both sexes. Immature females can be distinguished from juveniles by the presence of worn, dark-tipped outer coverts, fresh white-tipped inner coverts, and brown medial coverts that are tipped white. Juveniles cannot be sexed in the field through differences in plumage. In general, juveniles resemble adult females, but with darker wings, less-extensive wing bars, the lack of a malar (throat) patch, and the presence of a pink mandible (Jaramillo and Burke 1999).
Range mass: 29 to 43 g.
Range length: 16.8 to 19.3 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently; male more colorful
Length: 22 cm
Weight: 34 grams
Catalog Number: USNM 186125
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Birds
Preparation: Skin: Whole
Collector(s): J. Gaut
Year Collected: 1903
Locality: Del Rio, Val Verde, Texas, United States, North America
Bullock’s orioles prefer riparian corridors, open woodland, and scrub forest (Jaramillo and Burke 1999). During the breeding season, they are observed in patchy forest dominated by cottonwood and pecan throughout much of their range (Jaramillo and Burke 1999; Rising and Williams 1999). Willows (Salix) are preferred in riparian areas; by contrast, in arid southwestern Arizona this species prefers scrub forest trees, especially mesquite (Prosopis) and salt cedar (Tamarix) (Rising and Williams 1999). During the winter, Bullock’s orioles are often seen foraging in urban areas, particularly parks. In California, eucalyptus (Eucalyptus) is used as a source of nectar (Jaramillo and Burke 1999; Rising and Williams 1999).
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: savanna or grassland ; forest ; scrub forest
Other Habitat Features: suburban ; agricultural ; riparian
Habitat and Ecology
Comments: Open woodland, deciduous forest edge, riparian woodland, partly open situations with scattered trees, orchards, shade trees. In migration and winter also in humid forest edge, second growth, and scrub; Nests in trees, average of 8-9 m above ground, usually at end of drooping branch.
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Arrives in the northern U.S. and Canada in April-May; males precede females by a few days. Birds from most of breeding range apparently migrate to the southwestern U.S. for late summer, then continue later in fall southward into Mexico (Rohwer and Manning 1990).
Bullock’s orioles are primarily insectivorous. During the breeding season, they feed mostly on butterflies and their larvae (Lepidoptera) and augment their diet with beetles (Coleoptera), weevils (Curculionoidea), and scale insects (Coccoidea). Bullock’s orioles occasionally eat mollusks and small lizards. In one case, a member of this species was observed killing and eating a hummingbird. Fruit is also a major food source, accounting for approximately 40% of this species diet during the summer months (Sibley 2001). Stomach content analyses indicate that Bullock’s orioles especially favor cherries, blackberries, raspberries, and figs (Bent 1958). Bullock’s orioles either glean insects from leaves or forage in clearings. One behavior, common to the icterids, is called gaping: the bill is inserted into soil or a plant stem and then forced open. This behavior leaves an opening that may uncover prey species (Sibley 2001).
Animal Foods: birds; insects
Plant Foods: seeds, grains, and nuts; fruit; nectar
Primary Diet: carnivore (Insectivore )
Comments: Gleans insects, especially caterpillars, from trees and shrubs; also eats various fruits and nectar.
Bullock’s orioles help to spread the seeds of several plant species. Their eggs and young are a food source for several species and help keep insect populations in check. Please see the previous sections for more detailed information, especially “Food Habits” and “Predation”.
Ecosystem Impact: disperses seeds
Predators include jays, magpies, crows, and squirrels (Bent 1958; Jaramillo and Burke 1999). All four feed on the eggs or young of Bullock’s orioles. Nests are sometimes parasitized by cowbirds; however, Bullock’s orioles seem to be better able to identify parasitic eggs. They remove cowbird eggs by puncturing the shell with the bill and removing the egg from the nest, though an individual removing cowbird eggs in this manner risks damaging its own eggs (Bent 1958).
- Steller's jays (Cyanocitta stelleri)
- magpies (Pica)
- crows and ravens (Corvus)
- squirrels (Sciurus and Tamiasciurus)
Thought to be a solitary nester, but tends to aggregate nests (williams 1988). Females foraged regularly more than 200 meters from nest, and up to 1 kilometer away (Williams 1990).
Life History and Behavior
Vocalization forms the primary method of communication for Bullock’s orioles. Vocal communications include two short, energetic songs described by Dawson (1923) as kip, kit-tick, kit-tick, whew, wheet and cut cut cudut whee up chooup; the latter sequence is less common than the former. In the latter sequence, the last note is often unclear (Bent 1958). Both males and females sing, female song being lower in pitch and less sweet than that of the male. Females are most likely to sing earlier in the season, and have been observed to sing while constructing the nest. Males sometimes give a short cry while with their mate (Bent 1958). Baltimore and Bullock’s orioles have similar songs, though Baltimore orioles tend to have harsher songs than Bullock’s orioles (Bent 1958; Wheelock 1903).
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
The current observed maximum lifespan in the wild is 7 years, most individuals do not survive this long (USGS: Patuxent Wildlife Research Center).
Status: wild: 7 (high) years.
Lifespan, longevity, and ageing
Bullock’s orioles are seasonally monogamous, forming pair bonds that last for a single breeding season (Rising and Williams 1999).
Mating System: monogamous
Males arrive at the breeding ground approximately two weeks before females. Breeding begins in May and continues until mid July. The breeding season varies geographically and tends to begin and end later in the west and in northern latitudes (Jaramillo and Burke 1999; Harrison 1978; Rising and Williams 1999).
Bullock’s oriole nests are deep, pensile structures and are usually suspended on the outer branches of a tree (Harrison 1978). Nests are on average 6 inches (15 cm) deep and 4 inches (10 cm) in diameter, the walls of which are approximately 0.75 inches (1.9 cm) thick (Bent 1958). The nest opening is contracted and oval-shaped (Bent 1958). The nest is constructed primarily of plant fiber, especially flax fiber, oat stalks, and the interior bark of willow and juniper trees; horsehair and twine are also used when the nest is built near human developments. The nest is lined with plant down, wool, hair, and moss (Bent 1958; Harrison 1978). Both male and female have been observed to participate in nest construction, though normally only the female weaves the nest (Bent 1958). Nests are abandoned at the end of the breeding season and are not reused (Sibley 2000).
Eggs are laid in clutches of 3 to 6, with clutches of 4 or 5 eggs being the most common (Harrison 1978; Sibley 2000). The eggs themselves are small, approximately 2.5 cm long by 1.5 cm in diameter. Nest size is variable, and according to Schaefer (1976), nests range in depth from 10 cm to 38 cm. Eggs are whitish with dark purple or brown scrawling patterns near the wide end of the egg (Harrison 1978).
Breeding interval: Bullock's orioles breed once yearly.
Breeding season: Bullock's orioles breed from May through July.
Range eggs per season: 3 to 6.
Average eggs per season: 4.
Average time to hatching: 2 weeks.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Only the female incubates the eggs, which hatch after approximately two weeks (Harrison 1978). Nestlings are altricial: they are entirely reliant on parental care for their survival (Sibley 2000). Both sexes care for the young, providing them with food as well as defending the nest from predators (Bent 1958).
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Male, Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female)
Clutch size is 3-6 (commonly 4-5). Incubation, by female, lats 12-14 days. Young are tended by both parents, leave nest at 12-14 days. Ejects brown-headed cowbird eggs from nest (Sealy and Neudorf 1995, Condor 97:369-375).
Molecular Biology and Genetics
Barcode data: Icterus bullockii
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Icterus bullockii
Public Records: 5
Specimens with Barcodes: 6
Species With Barcodes: 1
Bullock’s orioles have declined in population size in North America since the 1960s, though this species is not considered endangered (Sibley 2001). Human factors contribute to this decline, through habitat degradation and the use of insecticides. An increase in habitat availability, caused by the planting of shelterbelts and by human control of brush fires, has probably led to population stability in the Great Plains. However, irrigation has reduced available water supplies in some parts of Kansas and Colorado, which likely negatively affects the carrying capacity for Bullock’s orioles in these regions. Unlike most migratory, riparian species, Bullock’s orioles have not seen a population decline in the Colorado River Valley (Rising and Williams 1999)
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5B - Secure
Rounded National Status Rank: N5B - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Relevance to Humans and Ecosystems
Bullock's orioles do not have any significant negative economic impact.
Bullock’s orioles regulate the populations of black olive scale insects (Parlatoria oleae), which in large numbers have the potential to destroy olive crops. Bullock’s orioles also consume cotton boll weevils (Anthonomus grandis), insects that can negatively impact cotton production (Bent 1958; Howell 1907). Bullock’s orioles are not known to have any significant negative impact on crop production.
Positive Impacts: research and education; controls pest population
|This article needs additional citations for verification. (July 2010)|
The Bullock's oriole (Icterus bullockii) is a small New World blackbird. At one time, this species and the Baltimore oriole were considered to be a single species, the northern oriole. This bird was named after William Bullock, an English amateur naturalist.
Bullock's orioles are sexually dimorphic, with males being more brightly colored than females. In addition, adult males tend to be slightly larger and heavier than females. In general, adults range in mass from 29 to 43 g (1.0 to 1.5 oz). Adults have a pointed bill with a straight culmen. In adult males, the tail is long, square, and jet black. All exposed skin is black, as are the claws and bill, though the base of the lower mandible lightens to bluish-gray.
Adult males are characterized by strongly contrasting orange and black plumage, a black throat patch and a white wing bar. The underparts, breast, and face are orange or yellow; by contrast, the back, wings, and tail are black. A black line extends from each eye to the black crown. The wing coverts (feathers not directly used in flight) are fringed white, forming a wing patch. Although the tail is mostly black, the outermost three or four retrices (flight feathers) are tipped orange, forming a T shape. Adult females, by contrast, have gray-brown upperparts, duller yellow on the breast and underparts, and an olive crown. Some females may also have a dark throat patch, similar (but less extensive) to the one found in adult males; in all cases females lack the black eye-line present in adult males. It is hypothesized that females with throat patches are older individuals.
Following the general pattern observed among icterids, the overall plumage pattern seen in immature male Bullock's orioles closely resembles that seen in adult females. Juveniles resemble adult females but have darker wings, fresh wing coverts, and a pink or whitish bill. Sexual dimorphism is not obvious in juveniles.
Bullock's orioles are seasonally monogamous. The breeding season typically lasts from May until July. The exact timing of the beginning of the breeding season tends to vary geographically: in general, breeding begins later in the northernmost and westernmost portions of its geographic range. Mated pairs of Bullock's orioles cooperate to weave deep, pendant baskets in which are deposited between three and six eggs, though females tend to do much of the work. The nest is woven of plant fibers, primarily bark and fine grass fiber, though animal hair is also commonly used. The nest is lined with down, hair, and moss.
Both males and females rear the young and defend the nest from predators and nest parasites.
Bullock's orioles and Baltimore orioles typically hybridize in the Midwest where their geographic ranges overlap.
Both males and females sing. While males have a sweeter voice, females tend to be more prolific singers. This bird's song is similar to that of the Baltimore oriole, but faster and somewhat more harsh.
Bullock's orioles are native to western North America, though according to Jaramillo (1999) they are sometimes found as vagrants in the eastern half of the continent. During the breeding season, they are found as far west as the eastern foothills of the Cascade range. Their breeding range stretches east to the Dakotas, Kansas, and northern central Texas. This species can be found as far north as British Columbia in Canada and as far south as Sonora or Durango in Mexico. It is common throughout its range, but is absent in parts of Arizona and Idaho where a combination of extreme elevation and an arid climate make for poor living conditions. During winter, this species retreats to Mexico and northern Central America. Its winter range extends south and east from Sinaloa to Oaxaca.
Like other members of Icteridae, Bullock's orioles prefer habitat edges. They especially prefer riparian corridors, open deciduous woodland, and scrub forest. Observations during the breeding season indicate that members of this species prefer areas with an abundance of cottonwood, pecan, and (if near water) willow. In dry areas, this species prefers salt cedar and mesquite. In California, eucalyptus trees are used as major sources of nectar.
These birds will readily come to a dish filled with grape jelly. Their parents lead the fledglings, feed them jelly and then the adult males leave the area. The young stay at the jelly dish from first feeding in early July and leave late September.
A member of the northern oriole group, Bullock's orioles were once considered to be conspecific with Baltimore orioles and black-backed orioles. However, recent phylogenetic data suggest that Bullock's orioles are members of a distinct species that does not share a most-recent common ancestor with Baltimore orioles, as was once assumed.
- BirdLife International (2012). "Icterus bullockii". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- "Birds of Nova Scotia - Northern Oriole". Nova Scotia Museum. 20 February 1998. Archived from the original on 2 April 2012. Retrieved 14 September 2011.
- Gough, G.A.; Sauer, J.R.; Iliff, M. (1998). "Patuxent Bird Identification InfoCenter" (version 97.1). Laurel, MD.: Patuxent Wildlife Research Center. Archived from the original on 19 August 2014. Retrieved 14 September 2011.
- Jaramillo, A.; Burke, P. (1999). New World Blackbirds: the Icterids. Princeton, NJ: Princeton University Press. ISBN 9780691006802.
- Rising, J.; Williams, P. (1999). Poole, A.; Gill, F., eds. Bullock's Oriole. The Birds of North America. Vol. 416 (Philadelphia, PA: The Birds of North America, Inc.). pp. 1–20.
|Wikimedia Commons has media related to Icterus bullockii.|
|Wikispecies has information related to: Icterus bullockii|
- Bullock's oriole Species Account - Cornell Lab of Ornithology
- Bullock's oriole - Encyclopedia of Life
- Bullock's oriole - Icterus bullockii - USGS Patuxent Bird Identification InfoCenter
- Bullock's oriole - BirdHouses101.com
- BirdLife species factsheet for Icterus bullockii
- Icterus bullockii on Avibase
- Bullock's oriole videos, photos, and sounds at the Internet Bird Collection
- Bullock's oriole photo gallery at VIREO (Drexel University)
Names and Taxonomy
Comments: Formerly considered conspecific with I. GALBULA and I. ABEILLEI under the name I. GALBULA (Northern Oriole) but resplit into separate species by AOU (1995). See AOU (1995, 1998) for a brief summary of the bases for the split.