Justification of Red List Category
This species is classified as Critically Endangered owing to its extremely small population which is thought to be declining as a result of habitat loss and hunting pressure.
Based on a range-size assumption of 100 km2, using density surface modelling and plot sampling extrapolations, the population was estimated to be between 347-4,578 individuals (Azevedo 2015). Assuming this species exists in the smallest area estimate of 55 km2 (Soares et al. 2020), the estimated population would therefore be roughly 190-2,500 individuals, which would roughly equate to 130-1,700 mature individuals.
The worst-case scenario of <200 individuals is not consistent with the number of ibises that hunters reported killing (Sampaio et al. 2016), however the best-case scenarios still produce very low population estimates.
The population is inferred to be declining as a result of ongoing hunting pressure (Sampaio et al. 2016). Hunting pressure is suspected to be high, but the resulting rate of decline is unclear. It may also be suffering habitat loss as a result of an oil palm plantation.
This species is endemic to São Tomé, São Tomé and Príncipe, where it is confined to the catchments of the Lembá, São Miguel, Xufexufe and the Quija rivers in the south-west, and of the Caué, Martim Mendes and Io Grande, in the south-east of the island (Soares et al. 2020).
It is thinly distributed in the south of the island, where it is reliably observed at a few locations, but never in large numbers (Olmos and Turshak 2007). It is thought to occupy an area of between 55 km2 (Soares et al. 2020) and 130 km2 (de Lima et al. 2017). There is one historical record from the north of the island, but no suitable habitat remains there (Christy and Clarke 1998).
Behaviour: This species is presumed to be sedentary (del Hoyo et al. 1992), even though there is strong indications of seasonal movements, including an even more restricted distribution during the breeding season (de Lima et al. 2017). Birds usually occur singly or in pairs (Borrow and Demey 2001), but sometimes in loose family groups (Olmos and Turshak 2010). Individuals roost together at night and can be identified as they call when flying to and from the roost (Olmos and Turshak 2010).
Habitat: The species is confined to forest below 1000 m, although most observations refer to birds in native forest at elevations up to 500 m (de Lima et al. 2017; Soares et al. 2020). However it can occur on secondary forest and neat palm plantations (Olmos and Turshak 2010; Soares et al. 2020). It appears to prefer flatter areas with higher tree densities and denser canopies (Ward-Francis et al. 2015). 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).
Diet: Its diet consists of invertebrates, snails and slugs (Christy and Clarke 1998).
Breeding: It is thought to breed during the rainy season (Ward-Francis et al. 2015), and has been recorded to be on eggs in November-December (Maia et al. 2014). In 1997 and 2009, nests were discovered in trees; the nest found in 1997 was overhanging water (S. d'Assis Lima in litt. 1998; BirdLife International 2008). It nests in branch bifurcations in small trees (Maia et al. 2014).
The greatest threat to this species is hunting, as it is a large, tame bird that prefers native lowland forests which are more accessible to hunters (Sampaio et al. 2016; de Lima et al. 2017; Soares et al. 2020). There is also evidence that current harvest rates are unsustainable to the extent that it might defy existing population estimates (Azevedo 2015; Sampaio et al. 2016). According to a recent survey, the species is taken opportunistically by hunters that normally target pigs and monkeys. However there are exceptions, notably at one location where villagers actively hunted the species (Ward-Francis et al. 2015; Sampaio et al. 2016).
Historically, large areas of lowland forest were cleared for cocoa plantations. Now abandoned, these plantations have created large extents of secondary forest (Oyono et al. 2014) that are mostly unsuitable for this species (Ward-Francis et al. 2015; de Lima et al. 2017; Soares et al. 2020). More recently, an oil palm palm plantation has promoted further habitat loss (Sampaio et al. 2016; de Lima et al. 2017). However, to ensure its environmental certification, this plantation envisages protecting the remaining forest (Socfin 2018). Forest palm-wine harvesting is widespread and affects areas close to where the species occurs, promoting easy access inside even the Obô Natural Park (Olmos and Turshak 2010). Timber extraction, and agricultural expansion and intensification are threatening the forest (Oyono et al. 2014), which poses a serious threat to the ibis. Infrastructure development arising from offshore oil extraction, and the population and economic boom is an additional threat (Oyono et al. 2014). 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 apparently ceased; however, future power projects remain a threat (Ward-Francis et al. 2015).
Introduced House Rat Rattus rattus, Mona Monkey Cercopithecus mona, African Civet Civettictis civetta and feral cats Felis catus are all potential predators (Dutton 1994).
Conservation Actions Underway
This species is considered protected by law 11/1999, and most of its range falls within the protected São Tomé Obô Natural Park. 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. 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). Between 2012 and 2015, as part of the BirdLife International Preventing Extinctions programme, a species action plan was defined, involving local and international stakeholders (Ndan'ang'a et al. 2014), and local community members were key in implementing research and monitoring into the ecology, population status, and threats (Ward-Francis et al. 2015; de Lima et al. 2017). 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). This species was chosen as one of a suite of indicator species to be monitored through regular surveys to assess the effectiveness for biodiversity conservation (BirdLife International 2019). There are several ongoing projects supporting forest conservation, for example ECOFAC6 (BirdLife International 2019).
Conservation Actions Proposed
Research ecological requirements, namely concerning breeding and feeding. Monitor hunting pressure, population size, and trends. Ensure the implementation of existing environmental laws, implement policies, raise awareness, and particularly reduce hunting pressure to sustainable levels. Training of staff is also required to ensure the protection of such areas. Ensure that any proposed hydroelectric dam developments are not within Obô Natural Park (Ward-Francis et al. 2015), and incorporate species conservation measures within the Obô Natural Park management plan, while developing capacity for park management (Ward-Francis et al. 2015). Formally recognise the proposed buffer zone, which encompasses several areas where birds have been recorded and that are currently unprotected (de Lima et al. 2017). Consider establishing a captive-breeding programme (Collar and Butchart 2013).
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.
Text account compilers
Allinson, T, Ashpole, J, Bird, J., Buchanan, G., Butchart, S., Ekstrom, J., Gascoigne, A., Grimmett, R., Melo, M., Pilgrim, J., Symes, A., Tavares, J., Taylor, J., Westrip, J.R.S., Wheatley, H., d'Assis Lima, S. & de Lima, R.F.
BirdLife International (2022) Species factsheet: Bostrychia bocagei. Downloaded from http://www.birdlife.org on 02/10/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 02/10/2022.