Dwarf olive ibis (Bostrychia bocagei)

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Dwarf olive ibis resting on branch, dorsal view
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Dwarf olive ibis fact file

Dwarf olive ibis description

KingdomAnimalia
PhylumChordata
ClassAves
OrderCiconiiformes
FamilyThreskiornithidae
GenusBostrychia (1)

Until its rediscovery in 1990, the only evidence for the continued existence of the dwarf olive ibis was from historical reports and anecdotes from hunters (2). Believed to be the world’s smallest ibis (3), this Critically Endangered species can be identified by the bare patches of black skin on the face and the large crest extending from the back of the head (4). The plumage is generally brownish, with a bronze sheen on the upperparts, and an olive hue on the head. Like other ibises, the dwarf olive ibis has a long, thin bill that curves downwards and, in this species, is coloured brown, becoming reddish towards the tip. Although often silent, when disturbed the dwarf olive ibis will make unusual cough-like grunts, while at other times it produces a kah gah kah gah call (2).

Size
Length: 60 – 65 cm (2)
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Dwarf olive ibis biology

In common with many other ibises, the dwarf olive ibis uses its long curved bill to probe within the soil and amongst rock crevices for its invertebrate prey. Generally, it prefers to forage in rocky, swampy areas of the forest with sparse undergrowth, or where the ground has been overturned by foraging wild pigs (2).

The dwarf olive ibis is usually found alone or in small flocks which roost together at night, announcing their entrance and exit from the roosting site with a harsh honking noise (2) (4). Little is currently known about this species’ reproduction, but a single nest was found in 1997 in a tree overhanging water (2).

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Dwarf olive ibis range

Endemic to the island of Sao Tomé, off the coast of Gabon in West Africa, the dwarf olive ibis occupies the areas around five rivers in the island’s central and south-western regions (2).

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Dwarf olive ibis habitat

The dwarf olive ibis is most commonly found in lowland primary forest below elevations of 450 metres, where it prefers swampy areas close to watercourses (2).

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Dwarf olive ibis status

Classified as Critically Endangered (CR) on the IUCN Red List (1).

IUCN Red List species status – Critically Endangered

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Dwarf olive ibis threats

The historical clearance of much of Sao Tomé’s lowland forest for sugar cane and cocoa plantations undoubtedly had a catastrophic impact on the dwarf olive ibis’s population (2) (5) (6). While today large-scale clearance for plantations has mostly stopped (2) (5), forest clearance for small farms continues, and there is also the possibility that exploitation of primary forest for timber and firewood will increase dramatically in the future (5). In addition, this species is severely affected by hunting and predation from introduced mammals such as the mona monkey (Cercopithecus mona), African civet (Civettictis civetta) and weasel (Mustela nivalis) (2). With its population estimated in 2007 to be between 50 and 249 individuals, the combined effects of these threats are rapidly pushing the dwarf olive ibis towards extinction (2).

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Dwarf olive ibis conservation

There are currently no conservation measures in place for the dwarf olive ibis. While various organisations have proposed that this species and its habitat should be given protected status, this has yet to occur (2) (6). Without intervention, this unique species, found nowhere else in the world, could disappear forever (2).

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

To learn more about Sao Tomé’s unique wildlife and the threats it faces visit:

For more information on this and other bird species please see:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
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Glossary

Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Invertebrate
Ananimal with no backbone.
Primary forest
Forest that has remained undisturbed for a long time and has reached a mature condition.
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References

  1. IUCN Red List (December, 2008)
    http://www.iucnredlist.org
  2. BirdLife International (December, 2008)
    http://www.birdlife.org
  3. Melo, M. (2004) Bird speciation in the Gulf of Guinea, West Africa. Genetics Society News, 51: 50 - 53.
  4. del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
  5. Peet, N. and Atkinson, P. (1994) Biodiversity and conservation of the birds in Sao Tomé and Principe. Biodiversity and Conservation, 3: 851 - 868.
  6. WWF (December, 2008)
    http://www.worldwildlife.org/wildworld/profiles/terrestrial/at/at0127_full.html
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Image credit

Dwarf olive ibis resting on branch, dorsal view  
Dwarf olive ibis resting on branch, dorsal view

© Nik Borrow

Nik Borrow
n.borrow@btinternet.com
http://web.mac.com/nikborrow

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