Bostrychia bocagei 


Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Pelecaniformes Threskiornithidae

Scientific Name: Bostrychia bocagei
Species Authority: (Chapin, 1923)
Common Name(s):
English Dwarf Ibis, Sao Tome Ibis
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Lynx Edicions BirdLife International.
Taxonomic Notes: Bostrychia olivacea (Sibley and Monroe 1990, 1993) has been split into B. olivacea and B. bocagei following Collar and Stuart (1985). Dwarf Olive Ibis Bostrychia bocagei of São Tomé differs from African Olive Ibis B. olivacea of West and Central Africa in size (wing of cupreipennis 309-355 mm, bill 83-94 mm, tarsus 58-70 mm, tail 125-133 mm [measurements of Príncipe race rothschildi similar]; wing of bocagei 248 mm [n=5] [i.e. 75%], bill 73 mm [82%], tarsus 52 mm [81%], tail 95 mm [74%]), bill colour (pale brown with pale red on culmen and tip vs all pale to brick red in rothschildi), and coloration of upperparts (lacking greenish and some bronze sheen of other races), plus an evident but still poorly documented difference in voice (rothschildi producing a typical "HAAN-ha HAAN-ha" at dawn and dusk, bocagei remaining mostly silent but occasionally delivering a more equally stressed "kàh-gàh kàh-gàh"). There is good precedent for allowing its specific status (i.e. Chapin 1923, Amadon 1953, de Naurois 1973).

Identification information: 60-65 cm. Small forest ibis. Adult has dull olive head and body with slightly bronzed mantle and wing-coverts. Dark area around eyes and base of bill. Voice Various coughed grunts when disturbed and harsh honking when going to roost.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered C2a(ii) ver 3.1
Year Published: 2015
Date Assessed: 2015-10-01
Assessor(s): BirdLife International
Reviewer(s): Symes, A.
Contributor(s): Carvalho, M., Gascoigne, A., Melo, M., d'Assis Lima, S. & de Lima, R.
Facilitator/Compiler(s): Bird, J., Butchart, S., Ekstrom, J., Pilgrim, J., Symes, A., Taylor, J., Allinson, T & Ashpole, J
This species is classified as Critically Endangered owing to its extremely small population which is declining as a result of hunting pressure.

Previously published Red List assessments:
2013 Critically Endangered (CR)
2012 Critically Endangered (CR)
2011 Critically Endangered (CR)
2010 Critically Endangered (CR)
2009 Critically Endangered (CR)
2008 Critically Endangered (CR)
2007 Critically Endangered (CR)
2004 Critically Endangered (CR)
2000 Critically Endangered (CR)
1996 Critically Endangered (CR)
1994 Critically Endangered (CR)
1988 Threatened (T)

Geographic Range [top]

Range Description: This species is endemic to São Tomé, São Tomé and Príncipe, where it is confined to the catchments of the São Miguel, Xufexufe and possibly the Quija rivers in the south-west, and along the Io Grande, Ana Chaves and Lembá rivers in the centre of the island (Ward-Francis et al. 2015). It was known only from historical records and anecdotal evidence from hunters until a confirmed sighting in the valley of the rio Ana Chaves, in 1990 (Atkinson et al. 1991). More records followed: birds were seen in 1996; two pairs, an individual and two nests were seen near the basins of the Rios Ió Grande (200 m asl) and Martim Mendes (100 m asl) in May 1997 in an area where hunters reported killing 16 of the birds 6 months previously (S. d'Assis Lima in litt. 1998); and during survey work in Ribeira Peixe in 2007 (Olmos and Turshak 2007). More recent fieldwork  resulted in 57 observations, including two nests with brooding females, in primary forest in the Monte Carmo area (Maia and Gascoigne in litt. 2010). A survey in July-September 2014 observed 48 individuals and one record of nest building (Ward-Francis et al. 2015). The most recent estimation suggests that the population is >50 individuals but remains extremely small (M. Melo in litt. 2006). It is apparently relatively widely, if thinly, distributed in the south. There is one historical record from the north of the island, but no suitable habitat remains there (Christy and Clarke 1998).

Countries occurrence:
Sao Tomé and Principe (Sâo Tomé)
Continuing decline in area of occupancy (AOO): Yes
Extreme fluctuations in area of occupancy (AOO): No
Estimated extent of occurrence (EOO) - km2: 210
Continuing decline in extent of occurrence (EOO): Unknown
Extreme fluctuations in extent of occurrence (EOO): No
Continuing decline in number of locations: Unknown
Extreme fluctuations in the number of locations: No
Upper elevation limit (metres): 750
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The most recent population estimate indicates that it is extremely small, and is best placed in the band 50-249 mature individuals (M. Melo in litt. 2006). This equates to 75-374 individuals in total, rounded here to 70-400 individuals.

Trend Justification:  Hunting pressure is suspected to be high with a recent report of 16 individuals being killed (S. d'Assis Lima in litt. 2006).

Current Population Trend: Decreasing
Additional data:
Number of mature individuals: 50-249 Continuing decline of mature individuals: Yes
Extreme fluctuations: No Population severely fragmented: No
No. of subpopulations: 1 Continuing decline in subpopulations: Unknown
Extreme fluctuations in subpopulations: No All individuals in one subpopulation: Yes
No. of individuals in largest subpopulation: 100

Habitat and Ecology [top]

Habitat and Ecology: Behaviour: This species is presumed to be sedentary (del Hoyo et al. 1992). Birds usually occur singly or in pairs (Borrow and Demey 2001) but roost together at night and can be identified as they call when flying to and from the roost (M. Melo in litt. 2006).

The species is confined to primary forest below 750 m (Ward-Francis et al. 2015), although suitable habitat could extend up to 800 m. However, it has been found most frequently in recent years at the border between primary and secondary forest, sometimes near palm plantations (M. Melo in litt. 2006). It appears to prefer flatter areas (Ward-Francis et al. 2015). Recent observations from Monte Carmo were from mature or old second-growth forest (Olmos and Turshak 2010). It forages on lowland forest floors on areas of bare ground or where there exists a sparse undergrowth of herbaceous plants, bracken and moss, a covering of rocks and large stones or around large trees with extensive buttresses (Christy and Clarke 1998, Olmos and Turshak 2010, Ward-Francis et al. 2015). It is especially found in areas where the ground has been disturbed by wild pigs or in swampy areas bordering watercourses or small oxbow lakes (Atkinson et al. 1991, Christy and Clarke 1998, Borrow and Demey 2001, Olmos and Turshak 2010).

Diet: Its diet consists of invertebrates, snails and slugs (Christy and Clarke 1998).

It breeds during the rainy season (Ward-Francis et al. 2015). A nest was found in 1997 in a tree overhanging water (S. d'Assis Lima in litt. 1998) and a nest found in 2009 was also in a tree (BirdLife International 2008)

Systems: Terrestrial
Continuing decline in area, extent and/or quality of habitat: Yes
Generation Length (years): 10.1
Movement patterns: Not a Migrant
Congregatory: Congregatory (and dispersive)

Threats [top]

Major Threat(s): Historically, large areas of lowland forest were cleared for cocoa plantations. Today, land privatisation is leading to an increase in the number of small farms and the clearance of trees (M. Melo in litt. 2006). This does not currently affect primary forest, but may be a threat in the future (A. Gascoigne in litt. 2000). Agricultural encroachment in the more accessible areas of Obô Natural Park was evident in 2007 and 2008, and hunting and palm-wine harvesting were widespread (Olmos and Turshak 2007, 2010), with shelters constructed inside the park (Olmos and Turshak 2010). Hunting may be the most serious current threat; the species is apparently very desirable for its meat and reports include 16 birds being killed in 1996-1997 (S. d'Assis Lima in litt. 2006), and six birds killed on a single occasion by one hunter (del Hoyo et al. 1992). Hunting pressure is believed to be increasing in the Monte Carmo area of the Obô Natural Park, one of the main strongholds for the species, and a group of hunters were found with at least one ibis in April 2011 (R. Grimmett in litt. 2011, Anon. 2011). A recent survey revealed that the extent of hunting was much greater than previously thought. However generally the species was not the target of hunters (whose main quarry was introduced pigs) and was instead taken opportunistically but the survey identified at least one exception where local villagers actively hunt the species (Ward-Francis et al. 2015).

Plans to develop coffee plantations and restore and extend 630 ha of abandoned palm-oil plantations (to cover more than 2,000 ha; ready for harvest in 2013) in the vicinity of the core zone of Obô Natural Park and encroaching into its buffer zone (J. Tavares in litt. 2010) may result in the loss of suitable habitat and potentially have both positive and negative influences on levels of disturbance (Olmos and Turshak 2010). The palm-oil project, however, reportedly incorporates the protection of some primary and mature secondary forest (J. Tavares in litt 2010). New road networks linking oil palm concessions may increase habitat fragmentation and disturbance (Ward-Francis et al. 2015). Road developments along the east and west coasts are increasing access to previously remote areas (A. Gascoigne in litt. 2000). Illegal logging in the south of the island has been identified as a further threat (Ward-Francis et al. 2015). Introduced Black Rat Rattus rattus, Mona Monkey Cercopithecus mona, African Civet Civettictis civetta and Weasel Mustela nivalis are all potential predators. In particular, recent reports suggest Mona Monkeys may be having a serious impact on productivity. A proposal to construct a hydroelectric dam within Obô Natural Park posed a very serious threat to key habitat for the species, this project has now ceased however future power projects remain a threat (Ward-Francis et al. 2015).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
Primary forest is protected as a zona ecologica and in the 295-km2 Obô Natural Park, although there is no law enforcement within these areas. The park was established in 1992, but was not protected by law until 2006, and although a zoning and management plan was being developed in 2008, when the first directors were appointed, the park was still lacking sufficient personnel (Olmos and Turshak 2010). A law providing for the gazetting of protected areas and the protection of threatened species has been ratified (M. Melo in litt. 2006). In 2008, a training programme with NGOs Associação de Biólogos Saotomenses (ABS) and Monte Pico was initiated to involve locals in the study and conservation of São Tomean species, and this has since been achieved (Associação dos Biólogos Santomenses in litt. 2010). Research is currently being carried out into the effects of agroforestry and the exploitation of wildlife resources on the island (del Hoyo et al. 1992, Borrow and Demey 2001). In 2013, work carried out by SPEA and funded by RSPB, mapped areas affected by oil palm plantations and surveyed for critically endangered species including Dwarf Olive Ibis (Barros 2013).

As part of the BirdLife International Preventing Extinctions programme, the Species Guardian ABS has begun training local community members in the implementation of site-based conservation; implementing an awareness raising campaign and carrying out field research and monitoring into the ecology, population status and threats to the species (BirdLife International 2008). During an international workshop held in February 2008 to promote ecotourism in São Tomé e Príncipe, birdwatching was listed as an activity that should be encouraged and Ribeira Peixe was identified as a suitable site for a pilot project (Olmos and Turshak 2010). In July 2009, ABS promoted a short course for the training of local people as bird guides at Ribeira Peixe and efforts were on-going to promote the conservation of the area (Olmos and Turshak 2010). The Government are developing an open access database to collate all biodiversity data for the island which will be used to inform land-use decisions (Ward-Francis et al. 2015). A workshop was held in January 2015, which included participants from the Government, to discuss progress towards an International Species Action Plan for the species (Ward-Francis et al. 2015).

Conservation Actions Proposed
Advocacy and awareness raising for species and primary forest protection in São Tomé. Identification of key sites and training of staff to ensure their protection. Ensure that any proposed hydroelectric dam developments are not within Obô Natural Park (Ward-Francis et al. 2015). Field research to improve knowledge on ecology, status and threats and mapping of protection zone for the species. Implement a monitoring strategy for the species. Formulate species conservation measures based on research findings and seek wider involvement in their implementation. Incorporate species conservation measures within the Obô Natural Park management plan and develop capacity for park management (Ward-Francis et al. 2015). Ensure legal protection of all remaining lowland primary forest. List it as a protected species under national law and consider establishing a captive-breeding programme. Promote access to cheaper sources of protein to reduce hunting of the species (Anon. 2011). Raise awareness of the species among the hunting community, undertake activities to encourage hunters to avoid taking the species, including through effective enforcement (Ward-Francis et al. 2015).

Citation: BirdLife International. 2015. Bostrychia bocagei. The IUCN Red List of Threatened Species 2015: e.T22697478A79118705. . Downloaded on 02 December 2015.
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