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Icterus oberiMontserrat oriole

By Ryan Ihnacik

Geographic Range

Icterus oberi is endemic to the island of Montserrat and is the island's national bird. A small protectorate of the United Kingdom, Montserrat is only 102 km2 in area. These birds are commonly known as Montserrat orioles. A combination of catastrophic volcanic activity that started in 1995 and has continued to the present, and frequent hurricanes have decimated the birds’ population. The species is in danger of extinction. ("Montserrat Oriole Reseach Details - The Royal Society for the Protection of Birds", 2006; Jaramillo and Burke, 1999; "CIA World Factbook", 2006)

Habitat

Montserrat orioles are found in the humid mountain forests of their small eastern Caribbean island home. These unique birds seem to prefer areas of dense vegetation, at high altitudes, where the air is cooler. (Jaramillo and Burke, 1999; Raffaele, et al., 1998)

  • Range elevation
    230 to 800 m
    754.59 to 2624.67 ft

Physical Description

Montserrat orioles are the only sexually dimorphic, sedentary, tropical orioles. In males, the tail and wings are entirely black, as well as the breast. The belly, rump, and the lower back are yellowish-tawny. Females are yellowish olive from the face down the belly to the rump. Their wings are a darker olive brown, and their tails are olive. Immature males closely resemble mature females, yet they have darker backs, and may have a few black throat feathers. Juveniles also resemble mature females, but they have a yellow wash about their rumps, underparts, and crowns, greenish-yellow faces, and olive flanks. (Jaramillo and Burke, 1999)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range wingspan
    88 to 98.5 mm
    3.46 to 3.88 in
  • Average wingspan
    92.6 mm
    3.65 in

Reproduction

Montserrat orioles breed seasonally. Males sing, however infrequently, to attract females. Females build hanging nests from vegetative matter, without the help of males. Montserrat orioles are monogamous. (Jaramillo and Burke, 1999)

Montserrat orioles nest yearly, from June to August. Their long, hanging nests are built from vegetation. Like many other species in the genus Icterus, nests are pendulous baskets. (Jaramillo and Burke, 1999; Raffaele, et al., 1998)

  • Breeding interval
    Montserrat orioles breed once yearly.
  • Breeding season
    Breeding occurs from June to August.
  • Range eggs per season
    2 to 4
  • Range time to hatching
    12 to 14 days
  • Range fledging age
    13 to 14 days
  • Average fledging age
    13 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    2 years

Eggs are incubated only by the female, yet both parents feed and care for their young. Females incubate the eggs for about two weeks until the young hatch. The young remain in the nest for another two weeks, until they fledge. Parents can be observed with their fledgling young, continuing to feed them for varying lengths of time. ("Montserrat Oriole", 2001; Jaramillo and Burke, 1999)

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

Lifespan/Longevity

There is no published data available on the lifespan of Montserrat orioles. However, with a captive breeding program underway at the Jersey Zoo, lifespan data may be forthcoming. ("Montserrat Oriole", 2001)

Behavior

Montserrat orioles spend much of their time foraging for insects on the undersides of leaves in dense mountain forests. They are active during the day. They are usually seen either alone or in pairs, unless they are still watching after their recently fledged young. (Jaramillo and Burke, 1999)

Home Range

There is no published data on the size of Montserrat oriole territories.

Communication and Perception

Montserrat orioles call only in the breeding season, during which they call infrequently. The call is composed of single notes, sung at intervals of 2.5 to 3 seconds, comparable to the tempo red-eyed vireo vocalizations. The notes are generally only one or two short syllables or low gurgles. Siegel (1983) described the call as a sharp "chic" or sharper "chuck," while Raffaele et al. (1998) describe as a "series of loud whistles and a harsh, scolding chuur call." (Jaramillo and Burke, 1999; Raffaele, et al., 1998; Siegel, 1983)

Food Habits

Montserrat orioles are thought to be almost entirely insectivorous in the wild, foraging for insects on the undersides of leaves. Frugivorous feeding has not been well documented in the wild, but a captive population at the Jersey Zoo is fed papaya and mango. Montserrat orioles have not been observed eating nectar. ("Montserrat Oriole", 2001; Jaramillo and Burke, 1999; Raffaele, et al., 1998)

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

Predation

Researchers from the Royal Society for the Protection of Birds studied predation of Montserrat oriole nests through the use of infrared micro-cameras. Very high rates of predation by rats were observed; it was thought that most nesting failures were a result of rat predation. ("Montserrat Oriole Reseach Details - The Royal Society for the Protection of Birds", 2006)

Ecosystem Roles

As the ecosystem of Montserrat has been perturbed so much through human deforestation and volcanic activity, and because there are so few Montserrat orioles left, it is hard to evaluate their ecosystem roles. However, as they do prey on insects, they may have a role in controlling insect populations. Volcanic ash-falls have negatively impacted insect populations, and subsequently decreased the amount of food available to Montserrat orioles. The degree to which they eat fruit in the wild is not well understood, but it is unlikely that they are instrumental in seed dispersal or pollination. Populations of introduced rats frequently prey on the nests of I. oberi, resulting in a high percentage of nest failure. ("Montserrat Oriole Reseach Details - The Royal Society for the Protection of Birds", 2006; "Montserrat Oriole", 2001)

Economic Importance for Humans: Positive

These birds provide a novel opportunity for the study of the evolution of sexual dimorphism. While their rareness makes them an exotic species for observation, most of their habitat is within restricted zones on Montserrat, making casual birding quite difficult. ("Montserrat Oriole Reseach Details - The Royal Society for the Protection of Birds", 2006)

  • Positive Impacts
  • ecotourism
  • research and education

Economic Importance for Humans: Negative

Negative economic impacts on humans are highly unlikely, due to their small population numbers.

Conservation Status

Since 2000, I. oberi has been listed by the IUCN as a critically endangered species. The IUCN outlines several reasons for decline of Montserrat orioles, including habitat destruction due to agriculture, invasive alien predators, drought, flooding, and the island's infamous volcanic eruptions.

Other Comments

Montserrat orioles are the only sedentary tropical orioles that are sexually dimorphic. Phylogenetic analysis of mtDNA indicates that Montserrat orioles are members of a group of Caribbean Island orioles. Icterus oberi is most closely related to two other species in the Lesser Antilles: Icterus laudabilis and Icterus bonana. (Omland, et al., 1999)

Researchers at the University of Maryland are attempting to understand why plumage is not brightly colored in females of this species, and why other tropical non-migrant species of the genus Icterus have bright plumage in both males and females.

Icterus oberi is in grave danger of extinction. It poses an immense challenge for conservation, and could likely become extinct in the wild within the next few decades. However, the captive breeding program at the Jersey Zoo aims to prevent the loss of this unique species. The threatened existence of Montserrat orioles serves as a grim reminder of both the degree to which human activities can impact other organisms, and how unforgiving the geological and meteorological systems of this planet can be. ("Montserrat Oriole", 2001)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Ryan Ihnacik (author), University of Maryland, Baltimore County, Kevin Omland (editor, instructor), University of Maryland, Baltimore County.

Glossary

Neotropical

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

World Map

acoustic

uses sound to communicate

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

cooperative breeder

helpers provide assistance in raising young that are not their own

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.

island endemic

animals that live only on an island or set of islands.

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).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

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.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

tactile

uses touch to communicate

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.

visual

uses sight to communicate

References

2006. "2006 IUCN Red List of Threatened Species" (On-line). Accessed November 15, 2006 at http://www.iucnredlist.org/search/details.php/10775/summ.

The Central Intelligence Agency of the United States of America. 2006. "CIA World Factbook" (On-line). Accessed November 01, 2006 at https://www.cia.gov/cia/publications/factbook/geos/mh.html.

2006. "Montserrat Oriole Reseach Details - The Royal Society for the Protection of Birds" (On-line). The Royal Society for the Protection of Birds. Accessed November 01, 2006 at http://www.rspb.org.uk/international/science/montserratoriole/research_details.asp.

2001. "Montserrat Oriole" (On-line). Jersey Zoo. Accessed November 08, 2006 at http://www.jerseyzoo.co.uk/.

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

Omland, K., S. Lanyon, S. Fritz. 1999. A Molecular Phylogeny of the New World Orioles (Icterus): The Importance of Dense Taxon Sampling. Molecular Phylogenetics and Evolution, 12: 224-239.

Raffaele, H., J. Wiley, O. Garrido, A. Keith, J. Raffaele. 1998. A Guide to the Birds of the West Indies. Princeton, New Jersey: Princeton University Press.

Siegel, A. 1983. The Birds of Montserrat. Montserrat, West Indies: Montserrat National Trust.

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