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Icterus galbulaBaltimore oriole

By Kathleen Bachynski and Sara Kennedy

Geographic Range

Baltimore orioles are neotropical migrants. They spend summers in the Nearctic, primarily the eastern United States. They breed from Wisconsin to Maine and south to central Mississippi and Alabama, northern Georgia, and western South Carolina and North Carolina. They winter in the neotropics as far north as Mexico and sometimes the southern coast of the United States. (Harrison, 1975; National Geographic Society, 1999; Peterson, 1980; Peterson, 1990)

Habitat

Baltimore orioles prefer open woods, with a strong preference for deciduous over coniferous trees. They are very adaptable, however, and can be found breeding in a variety of habitats. They are rare on farmlands but have adapted well to urban parks and suburban landscapes. In Mexico, they winter in flowering canopy trees over shade coffee plantations. (Greenberg, et al., 1997; Jobin, et al., 1998; Peterson, 1980; Rising and Flood, 1998)

Physical Description

Adult birds are 17 to 20 cm long, somewhat smaller than a robin. There is sexual dimorphism in plumage and in size; males are 1-5% larger than females in a variety of measurements. Adult males have a black head, bill, and back, and a bright orange breast, rump, and underparts. Their wings are black with orange and white wing bars, and the tail is orange with black streaks. Adult females are paler than males, olive-brown to orange. Their wings are brown with white wing bars, and the bill is gray. She may have traces of black on her head. Immature animals are variable, but typically resemble the female. Males take over a year to reach adult plumage. (National Geographic Society, 1999; Peterson, 1980; Tekiela, 1999)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    28 to 42 g
    0.99 to 1.48 oz
  • Range length
    17 to 20 cm
    6.69 to 7.87 in
  • Range wingspan
    9 to 10 cm
    3.54 to 3.94 in
  • Average basal metabolic rate
    0.5052 W
    AnAge

Reproduction

Baltimore orioles are generally considered monogamous, although evidence suggests that extra-pair copulation is reasonably common. In the spring, males display to females on their territory by singing and/or chattering while hopping from perch to perch in front of her. Males give a bow display, bowing with wings lowered and tail fanned. Some females ignore these displays while others sing and give calls or a wing-quiver display in response. The wing-quiver display involves leaning forward, often with tail partly fanned, and fluttering or quivering slightly lowered wings. (Rising and Flood, 1998)

Males arrive on breeding grounds in the spring a few days before females. Courtship displays by the male consist of bowing, to show off the bright orange front and black back, and singing. The female builds a woven pouch nest hanging from the end branches of trees, well concealed by leaves. She builds a new nest each year with little or no help from the male. Icterus galbula prefers to build in elms, maples, willow, or apples, twenty-five to thirty feet above the ground. Any available plant and animal fibers may be used.

The female lays four to six eggs, typically four. The eggs are pale grayish or bluish white, irregularly blotched and streaked with browns and black. The female incubates for twelve to fourteen days. Both parents feed the nestlings. Fledglings will stay with their parents for two weeks, and are fed by their parents duing that period. Baltimore orioles lay only one brood per season. (Bent, 1965; Harrison, 1975)

  • Breeding interval
    Baltimore orioles breed once yearly.
  • Breeding season
    Breeding occurs from May to June.
  • Range eggs per season
    3 to 7
  • Average eggs per season
    4
  • Average eggs per season
    4
    AnAge
  • Range time to hatching
    11 to 14 days
  • Average time to hatching
    12 days
  • Average time to independence
    2 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

The female alone broods nestlings; the male occasionally feeds the brooding female, but she usually forages for herself. Parents feed nestlings by regurgitation during the first few days of the nesting period. (Rising and Flood, 1998)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

The oldest recorded Baltimore oriole in the wild lived to 11 years and 7 months old. They have been recorded living 14 years in captivity. (Rising and Flood, 1998)

  • Range lifespan
    Status: wild
    11.5 (high) years
  • Range lifespan
    Status: captivity
    14 (high) years
  • Average lifespan
    Status: wild
    139 months
    Bird Banding Laboratory

Behavior

Icterus galbula is not a gregarious species. Like most icterids its flight is strong and direct. These birds are active during the day and migrate between summer and winter ranges. (National Geographic Society, 1999; Tekiela, 1999)

Home Range

Territory size varies with habitat quality, food availability, population density, and time of breeding season. It is largest when the male is attempting to attract a female and smallest after eggs are laid. (Rising and Flood, 1998)

Communication and Perception

The male sings all summer. His song is rich and flute-like, with each individual having a distinct song. The female song is generally shorter and simpler. The call, from both sexes, is a whistled "hew-li." Nestlings beg loudly.

Baltimore orioles also use postures and movements to communicate, such as male courtship displays, female wing-flutter displays, and nestling wing-flutters when begging for food.

Food Habits

Baltimore orioles eat primarily caterpillars, including many pest species. They also eat other insects, some small fruits, and nectar. They are an important predator of the nuisance forest tent caterpillar, Malacosoma disstria, which it eats in both its larval and pupal forms. Large larvae are seized and smashed against a twig to break them open and avoid the setae (stiff, hair-like structures). Pupae are pulled out of their cocoon.

In suburban and rural areas, I. glabula can be attracted to feeders by providing orange halves, grape jelly, or artificial nectar. Adults who come to feeders will take their young to the feeder once they are fledged. (Bent, 1965; Parry, et al., 197; Tekiela, 1999)

Baltimore orioles eat primarily caterpillars, including many pest species. They also eat other insects, some small fruits, and nectar. They are an important predator of the nuisance forest tent caterpillar, which it eats in both its larval and pupal forms. Large larvae are seized and smashed against a twig to break them open and avoid the setae (stiff, hair-like structures). Pupae are pulled out of their cocoon.

In suburban and rural areas, Baltimore orioles can be attracted to feeders by providing orange halves, grape jelly, or artificial nectar. Adults who come to feeders will take their young to the feeder once they are fledged.

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

Predation

Baltimore orioles have many different kinds of predators, including larger birds and mammals. Most predators take eggs, nestlings, or fledglings. In western Massachusetts, avain predators caused 16% of egg losses and 9% of nestling and fledgling losses. In response to predators, both males and females give alarm calls, and chase and mob (harass) predators. (Rising and Flood, 1998)

Ecosystem Roles

Baltimore orioles are important predators on insects in the communities in which they live. Because they live in forested areas and prey on caterpillars, the lifestage at which many insects do most damage to plants, they are especially important in protecting forest trees from damage.

Economic Importance for Humans: Positive

Baltimore orioles are attractive songbirds that will come to feeders. They are generally liked by both serious birdwatchers and casual backyard enthusiasts for both their appearance and song. They are also important predators on some insect pests such as forest tent caterpillars. (Bent, 1965; Parry, et al., 197)

  • Positive Impacts
  • ecotourism
  • controls pest population

Economic Importance for Humans: Negative

Baltimore orioles may occasionally damage crops of peas or small fruits. (Bent, 1965)

  • Negative Impacts
  • crop pest

Conservation Status

Baltimore orioles are protected by the Migratory Bird Treaty Act. They may be at risk due to habitat loss, as they prefer wooded areas, but this is not well documented. Although direct human impacts on oriole populations are unknown, the increase in number of orioles wintering in temperate North America may be due to an increase in bird feeders in backyards and elsewhere. (Rising and Flood, 1998)

Other Comments

Baltimore orioles were previously considered a supspecies of northern orioles (Icterus galbula galbula) along with Bullock's orioles (Icterus glabula bullockii), a western North American oriole. They are currently considered separate species: Baltimore orioles, Icterus galbula, and Bullock's orioles, Icterus bullockii. Some hybridization occurs in the Great Plains where these species overlap. (Gill, 1995; Peterson, 1990)

Contributors

Kathleen Bachynski (author, editor), University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Sara Kennedy (author), University of Michigan-Ann Arbor, Terry Root (editor), University of Michigan-Ann Arbor.

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.

arboreal

Referring to an animal that lives in trees; tree-climbing.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

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

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

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.

insectivore

An animal that eats mainly insects or spiders.

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).

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.

oviparous

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

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

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

scrub forest

scrub forests develop in areas that experience dry seasons.

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

solitary

lives alone

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.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

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

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

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

Gill, F. 1995. Ornithology. New York: W.H. Freemand and Company.

Greenberg, R., P. Bichier, J. Sterling. 1997. Bird populations in rustic and planted shade coffee plantations of Eastern Chiapas, Mexico. Biotropica, 29 (4): 501-514.

Harrison, H. 1975. A field guide to birds' nests. Boston: Houghton Mifflin Company.

Jobin, B., J. Des Granges, C. Boutin. 1998. Farmland habitat use by breeding birds in southern Quebec. Canadian Field-Naturalist, : 611-618.

National Geographic Society, 1999. Field guide to the birds of North America. Washington, D.C.: National Geographic Society.

Parry, D., J. Spence, W. Volney. 197. Responses of natural enemies to experimentally increased populations of the forest tent caterpillar *Malacosoma disstria*. Ecological Entomology, : 97-108.

Peterson, R. 1980. A field guide to the birds. Boston: Houghton Mifflin Company.

Peterson, R. 1990. A field guide to western birds. Boston: Houghton Mifflin Company.

Rising, J., N. Flood. 1998. Baltimore Oriole. The Birds of North America, No. 384: 1-32.

Tekiela, S. 1999. Birds of Michigan field guide. Cambridge, Minnesota: Adventure Publications, Inc..

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