Montserrat oriole (Icterus oberi)

Description

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Montserrat oriole fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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Montserrat oriole description

A Critically Endangered species teetering on the edge of extinction, the Montserrat oriole (Icterus oberi) clings to a precarious existence under the constant shadow of an active volcano, which has already destroyed around a third of its habitat. The national bird of Montserrat, where it is a flagship species for the conservation of the island’s threatened fauna, this iconic species is the subject of much research and management and should hold on to survival, assuming there is no further volcanic activity ^{(3) (4)}. 

The Montserrat oriole is a striking bird which, unusually for an Icterid, displays marked sexual dimorphism. The male is mostly black, with bright yellow on the lower back, rump, shoulder, lower breast and belly. The underparts of the tail are also yellow and have a wash of brown. The wings are largely black, except for some yellow on the bend and the under-wing coverts. The female is a somewhat duller yellowish-green on the upperparts, with bright yellow underparts. The juvenile is greenish with a black throat ^{(2) (5) (6)}. The Montserrat oriole may be further identified by its calls of loud whistles and harsh ‘churrs’ ⁽²⁾.

Size

Length: 20 - 22 cm ⁽²⁾

Montserrat oriole biology

The Montserrat oriole primarily feeds on insects, such as crickets and grasshoppers, which it catches mainly in the forest understory. It less frequently feeds on fruits, and has also been observed eating a nectar solution that gathers in the bracts of Heliconia plants. The Montserrat oriole is thought to be fairly opportunistic and have a flexible diet that varies with the availability of certain prey types ^{(2) (3)}. 

A monogamous species, the Montserrat oriole breeds between March and August, with the exact timing of breeding depending on the rainy season ⁽³⁾. Like many other Icterids, it builds a very intricate, elaborate nest which, in this case, is a basket-shape woven with dried plant fibres, that is sewn to and suspended from the leaves of Heliconia caribbaea. A clutch of usually two or three eggs is laid, and successful pairs may occasionally rear up to three broods per year. Unsuccessful pairs may attempt up to five clutches in a single season. ⁽²⁾. Incubation duties, which may be shared equally by both parents or have little input from the male, usually last for around 14 days. Both adults feed the chicks for the 13 days that they are in the nest, while post-fledging parental care may be prolonged, lasting over 3 months in some extreme cases ⁽³⁾.

Montserrat oriole range

The Montserrat oriole is found only on the volcanic island of Montserrat in the Lesser Antilles. It formerly occurred across the island’s three main forested hill ranges (the Centre, Soufrière and South Soufrière hills), but volcanic activity between 1995 and 1997 destroyed two-thirds of its habitat. Initially only the Centre Hills population was thought to have survived; however, later surveys discovered a remnant population occupying an area of just one to two square kilometres in the South Soufrière hills ⁽²⁾. 

The Montserrat oriole is occasionally also observed in agricultural and residential areas of lowland Montserrat, but this is likely due to individuals wandering from core population areas. In total, the Montserrat oriole is thought to occupy an area of less than 13 square kilometres ⁽³⁾.

Montserrat oriole habitat

This forest species occurs in most forest habitats on Montserrat, between elevations of 150 and 900 metres. However, it is found in greatest abundance in wetter, higher altitude forest, and is largely absent from lowland dry forest. The Montserrat oriole is often also found at the edges of cultivated areas and banana plantations ^{(2) (3)}. 

Montserrat oriole status

The Montserrat oriole is classified as Critically Endangered (CR) on the IUCN Red List ⁽¹⁾.

Montserrat oriole threats

Confined to hill forests on the small island of Montserrat, the Montserrat oriole is believed to have formerly had a total range of around 30 square kilometres ⁽⁷⁾. However, volcanic eruptions between 1995 and 1997 destroyed around two-thirds of its habitat, all but removing this species from the Soufrière and South Soufrière hills, and largely restricting it to just the Centre Hills. Initial surveys suggested that much of the population had survived the eruptions, with healthy numbers remaining in the Centre Hills and a smaller relict population in the South Soufrière hills. But between 1997 and 2003, the population declined very rapidly ^{(2) (3)}. The exact cause of this decline is unknown, but potential agents include ash fall on the forest causing insect availability to decrease or chronic ill health of birds ⁽²⁾. 

Drought between 2001 and 2004 also appeared to reduce laying frequency and clutch size, while the Montserrat oriole suffers high rates of predation by introduced rats and native pearly-eyed thrashers (Margarops fuscatus) ⁽³⁾. 

With a total population estimated at just 460 to 590 breeding birds, which occurs in 2 isolated pockets separated by lava flows and abandoned farmland, the Montserrat oriole is extremely vulnerable to any additional threats ⁽³⁾. Its populations are also at risk of further volcanic eruptions, as well as other natural destructive events, such as hurricanes, which are a frequent disturbance in the Caribbean region. A feral pig population is also spreading rapidly across Montserrat and could cause serious damage to forest habitat if it is not eradicated soon ⁽²⁾.

Montserrat oriole conservation

Since the devastating volcanic eruption that almost caused the extinction of this striking species, the Montserrat oriole has been the target of much research and management. In June 1999, eight birds were taken to Jersey Zoo to enable the development of husbandry techniques. Initial attempts at captive breeding proved successful and captive birds are now also present at several other locations in the UK ⁽²⁾. 

There are currently no plans to augment the wild population with birds from captive stock. However, there is much potential, and need, for a captive breeding programme, as this would safeguard the Montserrat oriole against the risk of extinction by providing birds for future reintroduction. Furthermore, captive birds can potentially be used to assist research into conservation management techniques. Development of artificial incubation and hand-rearing techniques, for example, would enable eggs or chicks to be harvested from wild nests and raised in a controlled environment, before being released back into the wild and increasing this species’ reproductive output ⁽³⁾. 

There is also a comprehensive programme to monitor the population and breeding success of the Montserrat oriole. In 2001, a new research programme into the causes of the continuing decline was begun, and the results of initial management interventions were assessed in 2003 ⁽²⁾. In addition, a Species Action Plan was published in 2005 ⁽³⁾. The Montserrat oriole should also benefit from experimental rat control in the Centre Hills, which commenced in 2006, as well as a pig eradication programme which is planned for the island ⁽²⁾. 

The Montserrat oriole is legally protected under the Wild Birds Protection Ordinance (1987), and the Forestry, Wildlife, National Parks and Protected Areas Ordinance (1996), which also makes provision for protected areas and wildlife protection. The majority of this species’ population is also afforded protection in the Centre Hills Forest Reserve, most of which is privately owned, with an agreement between the government and landowners ensuring the area is managed for the benefit of wildlife ⁽³⁾.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

Find out more about conservation on Montserrat:

• Montserrat National Trust:
  http://www.montserratnationaltrust.ms/
• UK Overseas Territories Conservation Forum:
  http://www.ukotcf.org/

Find out more about the Montserrat oriole and other birds:

• BirdLife International:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=9698

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Glossary

Bract

Modified leaf at the base of a flower.

Coverts

Small feathers concealing the bases of larger flight feathers, usually on the wings or tail.

Feral

Previously domesticated animals that have returned to a wild state.

Incubation

The act of incubating eggs, that is, keeping them warm so that development is possible.

Monogamous

Having only one mate during a breeding season, or throughout the breeding life of a pair.

Sexual dimorphism

When males and females of the same species differ in appearance.

References

1. IUCN Red List (March, 2011)
   http://www.iucnredlist.org/
2. BirdLife International (March, 2011)
   http://www.birdlife.org/datazone/speciesfactsheet.php?id=9698
3. Hilton, G.M., Gray, G.A.L., Fergus, E., Sanders, S.M., Gibbons, D.W., Bloxam, Q., Clubbe, C. and Ivie, M (Eds.) (2005). Species Action Plan for the Montserrat Oriole Icterus oberi. Department of Agriculture, Montserrat.
4. Schulenberg, T.S. (2010). Montserrat Oriole (Icterus oberi). In: Schulenberg, T.S. (Ed.) Neotropical Birds Online. Cornell Lab of Ornithology, Ithaca. Available at:
   http://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=673516
5. Bond, J. (1993) A Field Guide to Birds of the West Indies. Peterson Field Guides, Houghton Mifflin Company, New York.
6. Raffaele, H.A., Wiley, J., Garrido, O., Keith, A. and Raffaele, J. (2003) Birds of the West Indies. Princeton University Press, New Jersey.
7. Hilton, G.M., Atkinson, P.W., Gray, G.A.L., Arendt, W.J. and Gibbons, D.W. (2003) Rapid decline of the volcanically threatened Montserrat oriole. Biological Conservation, 11: 79-89.