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Icterus spuriusorchard oriole

By Lynna Kiere

Geographic Range

Orchard orioles breed in Canada, the United States, and Mexico. Their breeding range extends north to southeast Saskatchewan, through southwest Manitoba, southern Ontario, central New York and extreme southern Maine, along the entire east coast of United States through northern Florida, southwest from the Gulf coast of northern Florida through southern Texas (but absent from Rio Grande Valley), and into inland central Mexico to southern Guanajuato. The breeding range extends west to eastern Montana and Colorado, western Texas, and northwestern Oklahoma. (Jaramillo and Burke, 1999)

The winter range of orchard orioles includes both coasts of Mexico, through Central America, and northern South America. On the Pacific Coast they occur north to central Sinaloa and south to central Oaxaca, where they also occur inland. On the Gulf Coast they are found as far north as southern Tamaulipas and south to southern Veracruz, where they are also found inland. Orchard orioles are present on all of the Yucatan Peninsula and throughout Central America except the highlands of Guatemala and southern highlands of Nicaragua. They winter as far south as northern Colombia and northwestern Venezuela. (Jaramillo and Burke, 1999)

Orchard orioles migrate over southern Florida in large numbers, and have (very rarely) been recorded wintering there as well as southern Louisiana. (Jaramillo and Burke, 1999)

Habitat

Orchard orioles exhibit a preference for settling near a source of water, such as a lake or river, and may be found in narrow riparian zones, floodplains, or marshes (Jaramillo and Burke, 1999). They are rather adaptable to local ecosystems. In the summer nesting season, for instance, they are found in mesquite brushland in Texas, orchards in Pennsylvania, and phragmite marshes in Louisiana (Scharf and Kren 1996). During migrations, they often inhabit forest edges where flowering trees and fruits are available (Scharf and Kren 1996). While overwintering in their southern ranges, they are found in the same types of habitats: light woods in Colombia, plantations in Honduras, and tropical forests in Mexico (Scharf and Kren 1996). Overall they tend to avoid dense forest, preferring more open woods or edge habitats, and are not usually found in the dry inland scrub regions of Mexico (Scharf and Kren 1996). (Jaramillo and Burke, 1999; Scharf and Kren, 1996)

Orchard orioles are not particularly sensitive to human activity, and are found in suburbs, parks, and agricultural lands throughout their geographic range (Scharf and Kren 1996). (Scharf and Kren, 1996)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • Range elevation
    1300 (high) m
    4265.09 (high) ft

Physical Description

Orchard orioles are the smallest of the North American orioles, averaging 15 to 18 cm in length, with males marginally larger than females. They have a short, squared-off tail and small, slender bill. The legs and feet are blue-gray and the eyes are dark brown for both sexes (Jaramillo and Burke 1999). (Jaramillo and Burke, 1999)

Breeding adult males are black on the head, neck, upper breast, nape, back, and scapulars. The rump, upper-tail coverts, and underparts from breast to under-tail coverts are rich chestnut. The wings are primarily black, except for chestnut epaulets and white wing bar and tips. The tail is black with narrow brownish-white tips (Jaramillo and Burke 1999).

Non-breeding adult males look much like breeding males, but olive or pale chestnut-tipped feathers may obscure the black coloration on the upperparts. The feathers on the rump and upper tail-coverts as well as the underparts from the breast to the undertail-coverts may have yellowish tips. Brownish white or gray tips on the tail may be more noticeable than on the breeding male (Jaramillo and Burke 1999).

Second year males are similar to adult females, but have a solid black bib and black between the eye and bill. The degree to which black adult plumage appears in this stage varies considerably between individuals, with some males of this age having more black feathering than others (Scharf and Kren 1996). Despite their lack of adult coloration, these males are sexually mature. Though they can breed, they are often unsuccessful in finding a mate because females generally select males with adult plumage (reviewed in Enstrom, 1993).

Hatch year males are similar to adult breeding females, but with more greenish, yellowish, or brownish upperparts and brighter yellow underparts (Scharf and Kren 1996). Flecked black feathering on the throat and between the eye and bill is possible (Jaramillo and Burke 1999). (Enstrom, 1993; Jaramillo and Burke, 1999; Scharf and Kren, 1996)

Juvenile Orchard Orioles of both sexes are similar in appearance to adult females, but they are browner above and more yellow below (Scharf and Kren 1996). The wings are pale brown with dull white edges and two buff-white wing bars (Scharf and Kren 1996). The tail is yellowish olive green (Scharf and Kren 1996). The bill is tinged pink or orange at the base, fading with age to adult black and blue-gray (Jaramillo and Burke 1999). (Jaramillo and Burke, 1999; Scharf and Kren, 1996)

Breeding adult females look much like non-breeding adult females, but have brighter underparts, a more mottled appearance on the upperparts, and a yellow sheen on the underside of the tail. Non-breeding adult females are brownish olive from forehead to uppertail-coverts on upperparts. This coloring is brighter on the forehead, more yellow on the rump and uppertail-coverts, and fades to olive on the flanks (Scharf and Kren 1996). The back is dark olive and the wings are dark gray with two white wing bars and white edging (Jaramillo and Burke 1999, Scharf and Kren 1996). The tail is olive above and yellowish underneath (Jaramillo and Burke 1999).

Second year and hatch year females are similar to adult non-breeding females. The second year females are browner on the underparts and more uniformly brown (less mottled) on the upperparts than adult females (Scharf and Kren 1996). The hatch year females are browner above and brighter yellow below than adults (Scharf and Kren 1996). The transition between these two plumage patterns is slight, and may not be noticeable in the field (Jaramillo and Burke 1999). (Jaramillo and Burke, 1999; Scharf and Kren, 1996)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    16 to 25 g
    0.56 to 0.88 oz
  • Range length
    15 to 18 cm
    5.91 to 7.09 in

Reproduction

Both second year and full adult males arrive in breeding ranges at the same time in mid May. Females arrive either with the males or, in the most northerly parts of their range, soon after (Jaramillo and Burke 1999). Both females and males use courtship displays to attract mates, including “bowing” (the head is lowered) “seesawing” (the head and tail are bobbed alternately), and “begging” (the wings are fluttered and a high trill is sung). The male also uses a flight display, during which he seesaws while flying (Scharf and Kren 1996). (Jaramillo and Burke, 1999; Scharf and Kren, 1996)

After pair formation and copulation, females begin building a hanging cup-shaped nest (Scharf and Kren 1996). Orchard orioles generally prefer to build their nests in the fork of small branches in trees without a dense canopy, such as willows, elms, magnolia, and pecan (Scharf and Kren 1996). The nests are also commonly built in Spanish moss, and have more rarely been found in phragmites grasses (Dennis 1948). The nest takes the female about six days to complete and is woven from long strands of grass lined with animal hair, yarn, thin grass, feathers, or other available soft materials (though it may not be lined at all) (Scharf and Kren 1996). (Dennis, 1948; Scharf and Kren, 1996; Dennis, 1948; Scharf and Kren, 1996)

About seven days after the female begins building the nest, she lays between two and seven eggs, depending on geographic area (Clawson 1980). The eggs are light blue, with irregular purple or brown markings mostly on the larger end of the egg (Jaramillo and Burke 1999). (Clawson, 1980; Jaramillo and Burke, 1999; Clawson, 1980; Jaramillo and Burke, 1999)

The female incubates the eggs for 12-14 days, during which the male feeds her and may guard the nest (Johnsgard 1979, Foss 1994, Scharf and Kren 1996). Once the eggs hatch, the downy gray or buff-colored chicks are fed by both parents and fledge after 11-14 days in the nest (Scharf and Kren 1996). (Foss, 1994; Johnsgard, 1979; Scharf and Kren, 1996; Foss, 1994; Johnsgard, 1979; Scharf and Kren, 1996)

The fledglings remain in densely covered habitat close to the nest until the family unit disbands after about a week (Sealy 1980). Adult females and fledglings of both sexes stay in the area and feed mainly on fruits in late July and early August when the males have begun their fall migration (Scharf and Kren 1996). (Scharf and Kren, 1996; Sealy, 1980; Scharf and Kren, 1996; Sealy, 1980)

Orchard orioles are generally considered single-brooders, raising only one brood of offspring per season. When unseasonably harsh weather or other catastrophes destroy eggs early enough in the season, they may re-lay, raising one successful brood later in the breeding season (Scharf and Kren 1996). However, in 2004 three pairs of orchard orioles in Maryland were observed raising two successful broods in one season (Omland and Ligi, unpublished data). The second brood was laid as soon as a week to as late as a month after the young from the first brood had fledged (Omland and Ligi, unpublished data). Further research may help clarify the question of how prevalent this behavior is in orchard oriole populations. (Scharf and Kren, 1996; Scharf and Kren, 1996)

  • Breeding interval
    Orchard orioles typically breed once yearly.
  • Breeding season
    Breeding occurs from May through August.
  • Range eggs per season
    2 to 7
  • Average eggs per season
    4
  • Average eggs per season
    4
    AnAge
  • Range time to hatching
    12 to 14 days
  • Range fledging age
    11 to 14 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Both male and female orchard orioles play a role in parental care. Females build the nest and incubate the eggs. During incubation, males feed the female and protect the nest. When the chicks hatch, the male and female share the responsibilities of feeding the young and carrying away feces (Scharf and Kren 1996). After the young have fledged, the male and female remain to forage with the fledglings for about a week, after which the male begins the fall migration (Sealy 1980). When males leave, females and young may stay behind and feed in large flocks (Jaramillo and Burke 1999). (Jaramillo and Burke, 1999; Scharf and Kren, 1996; Sealy, 1980)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • male
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

The oldest orchard oriole recorded was recaptured in the wild at 9 years and 7 months old (Scharf and Kren 1996). (Scharf and Kren, 1996)

Behavior

Orchard orioles are relatively social both within and outside their species. During the breeding season, they often nest in loose colonies, warning each other of danger (Scharf and Kren 1996). They also nest near other species, (up to within a meter of western kingbirds, Tyrannus verticalis) which in some cases may be beneficial by reducing nest parasitism from cowbirds (Molothrus ater) (Scharf and Kren 1996). During the winter, they may roost in large numbers (sometimes more than 100), both with other orchard orioles and other species, including Baltimore orioles (Icterus galbula) and many species of finch (Fringillidae)(Bent 1965). (Bent, 1965; Scharf and Kren, 1996)

Orchard orioles are diurnal except during spring and fall migrations. They generally begin foraging at dawn, decrease activity around noon, and are inactive during the afternoon and evening. When weather interrupts foraging, however, it is resumed later in the day (Scharf and Kren 1996). During migration, they are nocturnal (Bent 1965). (Bent, 1965; Scharf and Kren, 1996)

Orchard orioles migrate in the spring and fall. They leave their wintering grounds (Central Mexico to Northern Colombia) March through April, and arrive in their breeding ranges (Eastern United States and Northern Mexico) late April through late May (Scharf and Kren 1996). They begin leaving the breeding ranges after the young have fledged in late July to early August, and arrive in wintering grounds around mid-August (Scharf and Kren 1996). (Scharf and Kren, 1996)

Home Range

Orchard orioles have been observed nesting semi-colonially with conspecifics, as well as in close proximity to other species, such as Baltimore orioles (Icterus galbula) and Bullock’s orioles (Icterus bullockii) (Scharf and Kren 1996). Orchard orioles are not fiercely territorial year-round, but during the breeding season adult males will defend nesting and foraging areas from second year males (Scharf and Kren 1996). (Scharf and Kren, 1996)

Communication and Perception

Females and young orchard orioles communicate vocally through short monotonal whistles (Scharf and Kren 1996). These vocalizations are especially common during mid-July to mid-August, after adult males leave the nesting grounds and before the females and young begin their fall migration (Scharf and Kren 1996). (Scharf and Kren, 1996)

Adult (including second-year) males sing upon reaching the breeding grounds, most likely in order to attract a mate, but perhaps to a limited degree to establish foraging and nesting areas (Scharf and Kren 1996). This song, a high-pitched series of notes that may include harsh interjections and downward slurs, is similar to that of Baltimore orioles (Icterus galbula) (Scharf and Kren 1996). A soft chuck and chatter may also be used (Scharf and Kren 1996). (Scharf and Kren, 1996)

Alarm calls comprised of chucks and chatters are used by orchard orioles to warn others of potential danger (Scharf and Kren 1996). Orchard orioles respond to these warning calls from their own species as well as similar calls from other species, such as Baltimore orioles (Icterus galbula) or Bullock’s orioles (Icterus bullockii) (Clawson 1980, Scharf and Kren 1996). Orchard orioles also use visual signals to attract mates (see Reproduction). (Clawson, 1980; Scharf and Kren, 1996)

Food Habits

During the breeding season (late April or early May to mid July), orchard orioles are mostly insectivorous, but also consume small, ripe fruits and berries, nectar, and small seeds (Thomas 1946, Dennis 1948, Bent 1965). Stomach content data from Maryland suggests that their diet consists of about 91% insects and 9% plant material during this season (Bent 1965). (Bent, 1965; Dennis, 1948; Thomas, 1946; Bent, 1965; Dennis, 1948; Thomas, 1946)

During their fall migration to southern wintering ranges (arriving as early as the beginning of July in Mexico) their diet incorporates more ripe fruits and berries such as mulberries and chokecherries, as well as nectar from roadside flowering trees and hedges in Mexico (Howell and Webb 1995). (Howell and Webb, 1995; Howell and Webb, 1995)

In winter ranges (early or mid July to January), they consume the nectar of tropical flowering trees and vines such as Erythrina fusca, fruits such as mistletoe Arceuthobium), and insects obtained from foliage (Scharf and Kren 1996). (Scharf and Kren, 1996; Scharf and Kren, 1996)

During spring migration, an abundance of blooming plants makes nectar a significant food source along with insects (Scharf and Kren 1996). Orchard orioles passing through Florida consume blooming black locust (Robinia pseudoacacia) nectar in large numbers (Bent 1965), and those in California have been observed frequently feeding at hummingbird feeders (Small 1994). (Bent, 1965; Scharf and Kren, 1996; Small, 1994; Bent, 1965; Scharf and Kren, 1996; Small, 1994)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • fruit
  • nectar
  • flowers

Predation

Common grackles (Quiscalus quiscula) in western Nebraska expel young chicks from orchard oriole nests and break unhatched eggs (Scharf and Kren 1996). Nest parasitism by bronzed cowbirds (Molothrus aeneus) and brown-headed cowbirds (Molothrus ater) is fairly common, with parasitism rates being recorded as high as 28% (Jaramillo and Burke 1999). In California, greater roadrunners (Geococcyx californianus) have been observed preying on orchard orioles (Binford 1971). (Binford, 1971; Jaramillo and Burke, 1999; Scharf and Kren, 1996)

Ecosystem Roles

Orchard orioles are omnivorous, consuming insects and spiders, fruits, nuts, and nectar. They may help stabilize insect populations through predation in their communities. Fruits consumed by orchard orioles pass quickly through the bird’s digestive system. The seeds contained by the fruit remain undigested, spreading the seeds to other areas through its defecation. (Scharf and Kren, 1996)

Though they consume nectar, they are not always pollinators of the species they feed on (Scharf and Kren 1996). For some species, such as the flowering trumpet creeper (Campsis radicans), the bird pierces the flower at the base to obtain the nectar, avoiding the stamens of the flower and not pollinating the plant (Bent 1965). For other species, such as Erythrina fusca, orchard orioles do serve as a main pollinator (Morton 1979). (Bent, 1965; Morton, 1979; Scharf and Kren, 1996)

Like many other bird species, orchard orioles are hosts for several types of parasites, including blood parasites and various mites (Scharf and Kren 1996). Nest parasitism by bronzed cowbirds (Molothrus aeneus) and brown-headed cowbirds (Molothrus ater) is fairly common, with parasitism rates being recorded as high as 28% (Jaramillo and Burke 1999).

  • Ecosystem Impact
  • disperses seeds
  • pollinates
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Orchard orioles prey upon the cotton boll weevil (Anthonomus grandis), a major crop pest for cotton farmers (Oberholser 1974). They are also predators of many other important agricultural pest species, including caterpillars, plant lice, beetles, and worms, making them quite beneficial to farmers (Bent 1965). (Bent, 1965; Oberholser, 1974)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Orchard orioles may cause some minor crop damage when nesting on plantations. They may consume small amounts of stamens from fruit trees, small cultivated berries and fruits (strawberries, raspberries, cherries), figs, and grapes (Bent 1965) (Bent, 1965; Bent, 1965)

  • Negative Impacts
  • crop pest

Conservation Status

Because of population declines since 1982, the American Birds Blue List considers orchard orioles a species of special concern (Scharf and Kren 1996). Overall, the eastern population is steady, but the central population has declined in recent years (Scharf and Kren 1996). (Scharf and Kren, 1996)

The main cause of population decline is thought to be loss or degradation of habitat. Destruction of riparian zones and other preferred areas might account for some of the population’s decline in the central range (Scharf and Kren, 1996). Pesticide spraying in orchards is another potential issue and has displaced birds in Texas and Pennsylvania (Oberholser, 1974; Scharf and Kren, 1996). (Oberholser, 1974; Scharf and Kren, 1996)

Orchard orioles are protected by the Migratory Bird Treaty Act of 1918, which prohibits hunting, trading, and disturbing the nests or eggs of orchard orioles (USFWS, 2002). ("USFWS Division of Migratory Bird Management", 2002)

Other Comments

Orchard orioles are considered a species complex consisting of two groups, orchard orioles (I.s. spurius) and Fuertes’s or ochre orioles (I.s. fuertesi). A third subspecies is also often considered, I. s. phillipsi. The classification of these groups is a subject of recent debate. There is uncertainty as to whether Fuertes’s orioles should remain classified as a subspecies of Icterus spurius, as they are now, or considered a separate species, as they were in the past (I. fuertesi) (Jaramillo and Burke, 1999). The plumage pattern of Fuertes’s orioles is basically identical to that of orchard orioles; females and young males of the two groups are virtually indistinguishable. However, unlike adult male orchard oriole chestnut coloring, adult male Fuertes oriole’s plumage is described as “ochre” or tan. There appears to be no color overlap between the groups (Tracy, Hofmann, Cronin, and Omland, unpublished data). (Jaramillo and Burke, 1999)

Recent research into the genetics of Fuertes’s and orchard orioles has suggested that they are genetically distinct enough to be considered two separate species. By analyzing similarities in the mitochondrial gene, cytochrome-b, Baker et al. (2003) developed a phylogenetic tree that shows how closely related different orchard and Fuertes’s oriole individuals are. The tree that resulted shows that nearly all Fuertes’s orioles tested were more closely related to each other than to any orchard orioles (Baker et al., 2003). (Baker, et al., 2003)

Several other factors may support the separation of orchard and Fuertes’s orioles into different species. Perhaps the most immediately obvious difference between the two groups is the difference in adult male coloration. Indeed, this may be a significant difference. Hofmann, McGraw, Cronin, and Omland (unpublished data) used spectral measurements (plumage reflectance) and biochemical analysis to determine which pigments are responsible for the bright colors of orchard and Fuertes’s orioles. The color difference is due to a difference in the relative concentration of melanin and carotenoid type pigments in the feathers of each species. The chestnut color of orchard orioles is predominantly produced by a melanin-based pigment, specifically phaeomelanins; carotenoids are present, but are masked by the melanin (Hofmann, McGraw, Cronin, and Omland, unpublished data). Adult male Fuerte’s orioles have a much lower concentration of phaeomelanins (although it is still a higher concentration than is found in females). In Fuertes’s orioles, phaeomelanins do not completely mask the carotenoid color as they do in orchard orioles; carotenoids and melanins both contribute (Hofmann, McGraw, Cronin, and Omland, unpublished data).

Other differences between orchard and Fuertes’s orioles are their geographic ranges and migratory habits. Orchard orioles migrate long distances from their breeding grounds in the United States and Canada to wintering ranges as far south as Colombia, while Fuertes’s orioles inhabit only a small range, breeding on the eastern coast of Mexico from southern Tamaulipas to southern Veracruz, and wintering on the Pacific coast of Mexico from Guerrero to Chiapas (Jaramillo and Burke 1999). (Jaramillo and Burke, 1999)

The genus Icterus contains 25 recognized species, many of which exhibit very similar plumage patterns despite being distantly related (Omland and Lanyon 2000). Orchard orioles are an excellent example of this phenomenon, called “convergence.” Orchard orioles have a distinct pattern that includes a black head, colored epaulets, and white wing bars. A nearly identical pattern is found in Baltimore orioles (I. galbula), which are distantly related to orchard orioles. Omland and Lanyon (2000) examined 44 specific feather patches to assess the similarity of patterns in different species of orioles (a process called scoring) and, upon comparing orchard and Baltimore orioles found that only four of the feather patches between the two species differed in pattern (2000). These instances of marked similarity between distantly related species occur repeatedly in Icterus. (Omland and Lanyon, 2000)

Contributors

Lynna Kiere (author), University of Maryland, Baltimore County, Kevin Omland (instructor), University of Maryland, Baltimore County.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

2002. "USFWS Division of Migratory Bird Management" (On-line). Birds protected by the Migratory Bird Treaty Act. Accessed April 19, 2005 at http://migratorybirds.fws.gov/intrnltr/mbta/mbtandx.html#alpha1.

Baker, J., E. Lopez-Medrano, A. Navarro-Seguenza, O. Rojas-Soto, K. Omland. 2003. Recent Speciation in the Orchard Oriole group: divergence of Icterus spurius spurius and Icterus spurius fuertesi. The Auk, 120(3): 848-859.

Bent, A. 1965. Life Histories of North American blackbirds, orioles, tanagers, and allies. New York: Dover Publications.

Binford, L. 1971. Roadrunner captures Orchard Oriole in California. California Birds, 2: 139.

Clawson, S. 1980. Comparative ecology of the Northern Oriole (Icterus galbula) and the Orchard Oriole (Icterus spurius) in Western Nebraska. Master's Thesis, University of Nebraska: Lincoln.

Dennis, J. 1948. Observations on the Orchard Oriole in the lower Mississippi Delta. Bird Banding, 19: 12-21.

Enstrom, D. 1993. Female choice for age-specific plumage in the Orchard Oriole: implications for delayed plumage maturation. Animal Behavior, 45: 435-442.

Foss, C. 1994. Atlas of breeding birds in New Hampshire. Arcadia: Audubon Society of New Hampshire.

Howell, S., S. Webb. 1995. A guide to the birds of Mexico and northern Central America. New York: Oxford Univ. Press.

Jaramillo, A., P. Burke. 1999. New World Blackbirds: The Icterids. Princeton: Princeton University Press.

Johnsgard, P. 1979. Birds of the great plains: breeding species and their distribution. Lincoln: Univ. of Nebraska Press.

Morton, E. 1979. Effective pollination of Erythrina fusca by the Orchard Oriole (Icterus spurius):coevolved behavioral manipulation. Ann. Mo. Bot. Gard., 66: 482-489.

Oberholser, H. 1974. The bird life of Texas Vol. 1. Austin: Univ. of Texas Press.

Omland, K., S. Lanyon. 2000. Reconstructing plumage evolution in Orioles (Icterus): repeated onvergence and reversal in patterns. Evolution, 54: 2119-2133.

Scharf, W., J. Kren. 1996. Orchard Oriole. Birds of North America, 255: 1-23.

Sealy, S. 1980. Breeding biology of Orchard Orioles in a new population in Manitoba. Can. Field-Nat, 94: 154-158.

Small, A. 1994. California birds: their status and distribution. Vista, CA: Ibis Publ. Co.

Thomas, R. 1946. An Orchard Oriole colony in Arkansas. Bird Banding, 17: 161-167.

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