Black-faced Sheathbill
Chionis minor
Number Of Mature
Individuals (Regional)
4 000 – 6 000
Regional
Population Trend
Decreasing
2025
Regional Category
Vulnerable
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CONTENTSOverview
Names
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IOC English Name: |
Black-faced Sheathbill |
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SA & IOC Scientific Name: |
Chionis minor |
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BirdLife International Taxonomy (scientific name): |
Chionis minor |
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Order: |
CHARADRIIFORMES |
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Family: |
Chionidae |
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Species name author: |
Hartlaub 1841 |
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Afrikaans: |
Kleinskedebek |
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Sesotho (South Africa): |
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Sesotho (Lesotho): |
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Siswati: |
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Zulu: |
insukakude yaseMarion |
Current Assessment Status
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2025 Regional Category [Criteria] |
VU [D2] |
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2024 Global Category [Criteria] |
LC (BirdLife International 2024) |
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Population size (Regional) |
4000 – 6000 individuals |
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Population size (Global) |
8700 – 13 000 (BirdLife International 2024) |
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Distribution size (EOO) (Regional) km2 |
c. 720 (breeding islands) |
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Distribution size (EOO) (Global) km2 |
809 000 (breeding/resident) |
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Distribution size (AOO) (Regional) km2 |
100 – 334 |
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Generation time |
24 years (calculated using data from McClelland 2013) |
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Status change reason |
Genuine Change in Status |
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Migrant (in the region) |
No |
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Regional endemic |
No |
Historic Listing Information
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2000 Regional Status |
NT [A1ace] |
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2015 Regional Status |
NT [D2] |
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Status change reason (if applicable) |
No change |
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2015 Population size (Regional) |
6000 mature individuals |
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2015 Global Status |
LC |
Reason for Inclusion
Reason for Inclusion in the Assessment
The species breeds on the Prince Edward Islands and was listed as Near Threatened in the 2000 and 2015 regional assessments.
Category Justification
Category Justification
Within the region, the Black-faced Sheathbill Chionis minor breeds only at two locations: Marion Island and Prince Edward Island. The potential future threat of a poisoning effect during the planned mouse eradication on Marion Island adds to its vulnerability. Consequently, the species qualifies as regionally Vulnerable under the restricted population Criterion D2.
Population Justification
The global population has been estimated at 8700 – 13 000 mature individuals (BirdLife International 2024). Estimates of numbers of Black-faced Sheathbills at the Prince Edward Islands are gauged from counts of birds undertaken in winter, when birds are not breeding and are most conspicuous. A complete count from Prince Edward Island is not yet available. From 1977-1997, the mean count (± SD) on the east coast of this island was 1408 ± 153 individuals (Huyser et al. 2000). In March 2011, 311 individuals were counted on the west coast of the island (Department of Forestry, Fisheries and the Environment (DFFE), unpub data). Therefore, there are probably at least 1700 individuals at Prince Edward Island, but the population may be as high as 2000 – 3000 individuals. At Marion Island, there were 3600 – 3800 individuals in 1976 (Burger 1979, Huyser et al. 2000) and 4211 ± 188 individuals in 2011 (McClelland 2013) with a steady increase from 2008 to 2011. Most recently, a population of 3183 ± 105 individuals was estimated on Marion Island from whole island counts conducted in 2021 and 2022 (Nelson Mandela University (NMU) and DFFE unpubl data), which suggests a decrease over the preceding decade of 2.8% per annum. The combined population of the Prince Edward Islands for the current assessment is therefore c. 4000 – 6000 individuals compared to 6000 birds estimated for the previous assessment. However, while confidence in the population estimate for Marion Island is high, no recent counts are available from Prince Edward Island thus making it unclear how accurate the total population count is.
Trend Justification
On Marion Island, where whole island counts are conducted every year, the population has decreased from 4211 ± 188 in 2011 to 3183 ± 105 in 2021/2022 (McClelland 2013, NMU and DFFE unpubl data). Population projections by McClelland (2013) suggest that the reproductive population is declining by 3% per year, which is similar to the observed decrease over the period 2011-2021 (2.8% per annum). The survival rates from McClelland (2013) are used to calculate a generation time as 1/adult mortality rate + age of first reproduction.
However, confidence in the rate of decline is low given that counts by independent observers in the same year can vary quite dramatically due to highly dynamic detection probability of sheathbills (McClelland 2013) and recent counts from Prince Edward Island are yet to be available.
Biology & Ecology
Taxonomy
The two species of sheathbills belong to a mono-generic family. The Greater (or Pale-faced/Wattled/Snowy) Sheathbill Chionis albus breeds on the Antarctic Peninsula and islands of the Scotia Arc and occurs as a non-breeding migrant at the Falkland Islands, Tierra del Fuego and the Patagonian coast (Jones 1963). Vagrant (ship-assisted) individuals of this species have reached the mainland of South Africa, Brazil and even England (Parkin and Knox 1994, Daudt et al. 2017 ). The second species is the non-migratory Lesser (or Black-faced) Sheathbill C. minor. Four sub-species of the latter are usually recognised: marionensis occurs on the Prince Edward Islands; crozettensis on the Crozet Islands; minor on the Kerguelen Islands; and nasicornis on Heard and McDonald Islands (Shirihai 2007). As the species is largely sedentary there is thought to be little (if any) genetic mixing among sub-species.
Identification
Measuring 38–41 cm and weighing 450–760 g, this all-white terrestrial scavenger resembles a mix between a pigeon and a chicken. It is dimorphic, with males being noticeably larger. The bird is completely white, except for a pink eye-ring and black bill with facial caruncles. Mature birds display a distinctive upturned sheath on the upper mandible, while juveniles have a less developed bill sheath. The legs are mottled in pinkish, purple, and black shades.
Distribution
The Black-faced Sheathbill is endemic to sub-Antarctic islands in the southwestern Indian Ocean. C. m. marionensis occurs only at the Prince Edward Islands, a South African territory. At Marion Island, it occurs almost exclusively along the coastline, but at Prince Edward Island it forages throughout the coastal plain and onto the plateau at up to 300 m (Huyser et al. 2000, PG Ryan pers. obs.). However, as Black-faced Sheathbills occur mostly within 1 km of the coast and the coastline of Marion Island is c. 72 km while that of Prince Edward Island is only c. 28 km, the minimum AOO of Black-faced Sheathbills at the Prince Edward Islands is c. 100 km2.
Ecology
Black-faced Sheathbills are omnivorous, feeding on carrion; prey stolen from albatrosses, penguins and Crozet Shags Leucocarbo melanogenis feeding chicks; eggs and small chicks of seabirds (especially penguins); faeces of birds and seals; intertidal algae and invertebrates; and terrestrial invertebrates (Burger 1981, Huyser et al. 2000). In summer, Black-faced Sheathbills forage mostly in penguin colonies, for example summer counts on Marion Island in 2021 show that 75% of sheathbills forage in King Penguin Aptenodytes patagonicus, Eastern Rockhopper Penguin Eudyptes filholi and Macaroni Penguin E. chrysolophus colonies (NMU unpubl data). Terrestrial invertebrates used to form an important winter food source on Marion Island (Burger 1981, Huyser et al. 2000), but invasive House Mice Mus musculus have caused populations of these invertebrates to decrease dramatically (McClelland et al. 2018). As a result, Black-faced Sheathbills now forage predominantly in King Penguin colonies and along the shore in winter (Huyser 2000, McClelland 2013, NMU unpubl data). Throughout the year, a small proportion of the Black-faced Sheathbill population also forages among Wandering Albatross Diomedea exulans, Crozet Shag and seal colonies (NMU unpubl data).
The species breeds during the austral summer, returning to the same territories usually near albatross, penguin or Crozet Shag colonies. Nest building commences in October, eggs are laid in December, hatching occurs in January, and fledged chicks are independent by the third week in March (Burger 1979). Nests are in cavities under lava boulders, in small caves or rarely in burrows of larger petrels, to provide shelter from predators and harsh climatic conditions. Chick mortality occurs from predation and starvation. Adult survival on Marion Island is 0.955–0.991 in summer and 0.930–0.979 in winter (Table 8 in McClelland 2013). The sex ratio of sheathbills on Marion Island is strongly skewed towards females while the Prince Edward Island population has an equal sex ratio, suggesting that the skew in sex ratio on Marion is due to ecological changes driven by invasive House Mice which disproportionately affect female fledglings (McClelland 2013).
Threats & Conservation
Threats
Black-faced Sheathbills are vulnerable to predation by Brown Skuas Catharacta antarctica, especially when foraging inland (Burger 1979, Huyser et al. 2000), but they do not form a major portion of the skua’s diet (Burger 1979, NMU unpubl data). Until they were removed from Marion Island in the early 1990s, feral cats Felis catus also killed Black-faced Sheathbills (Burger 1979). Starvation and inclement weather may kill fully-grown birds (Burger 1979). Competition for food with introduced House Mice may impact winter survival (Huyser 2000, McClelland 2013, NMU unpubl data). Breeding populations of both Macaroni and Eastern Rockhopper penguins on the Prince Edward Islands declined significantly during the 1990s (Crawford and Dyer 2006). While the rate of decline has slowed, this may affect the foraging of Black-faced Sheathbills in summer. A proposed bait drop to eradicate mice may negatively affect the population on Marion Island, with Black-faced Sheathbills being susceptible to both primary and secondary poisoning (Wanless et al. 2010). Disease outbreaks may also threaten Black-faced Sheathbills, although there have been no records of this on the Prince Edward Islands or elsewhere.
Conservation Measures Underway
It is not permitted to feed sheathbills at the Prince Edward Islands and measures are in place for waste management at all field huts and at the main research base to reduce the availability of food to scavengers. No access to Prince Edward Island is allowed except for bona fide research purposes at most every five years. Strict measures are in place to prevent accidental introduction of mice to this locality. The Prince Edward Islands are listed as a Ramsar Wetland of International Importance, as a Special Nature Reserve under the Environment Conservation Act (No 73 of 1989) and managed under the Prince Edward Islands Management Plan 1996. The Prince Edward Islands Marine Protected Area was proclaimed in 2013.
Conservation Measures Proposed
Annual monitoring of numbers of sheathbills at Marion Island should be continued and regular counts should be conducted at Prince Edward Island. Studies should continue to estimate the impact of the planned mice eradication on the population of Black-faced Sheathbills on Marion Island although the full impact of the eradication won’t be known until a bait drop occurs.
Research Priorities and Questions
- An up-to-date count of Black-faced Sheathbills at Prince Edward Island is urgently needed.
- Research on taxonomic separation between sheathbills at Marion and Prince Edward Islands is currently being pursued. Preliminary microsatellite data suggest weak spatial differences among sheathbills sampled on Marion and Prince Edward Island, with sheathbills from Prince Edward Island nesting among sheathbills sampled on the northern coast of Marion Island (S Miller et al. unpubl data). Should these results be confirmed, this indicates that sheathbills on Prince Edward Island are not an evolutionarily distinct clade, and could be used as a source population for re-establishing sheathbills on Marion Island should there be catastrophic mortality of sheathbills during the mouse eradication attempt.
Contributors & References
Assessor/s
Eleanor Weideman, Maëlle Connan
Reviewer/s
Peter Ryan
References
BirdLife International. 2024. Chionis minor. The IUCN Red List of Threatened Species 2024: e.T22693567A263717271. https://dx.doi.org/10.2305/IUCN.UK.2024-2.RLTS.T22693567A263717271.en. [Accessed on 13 February 2025].
Burger AE. 1979. Breeding biology, moult and survival of Black-faced Sheathbills Chionis minor at Marion Island. Ardea 67: 1–14.
Burger AE. 1981. Food and foraging behaviour of Black-faced Sheathbills at Marion Island. Ardea 69: 167–180.
Crawford RJM, Dyer BM. 2006. Breeding numbers and success of Eudyptes penguins at Marion Island, and the influence of mass and time of arrival of adults. CCAMLR Science 13: 175–190.
Daudt NW, Pereira A, Rechetelo J, Krul R, Mestre LAM. 2017. Noteworthy seabird records from Paraná state, southern Brazil. Bulletin of the British Ornithologists’ Union 137: 195– 205.
Huyser O, Ryan PG, Cooper J. 2000. Changes in population size, habitat use and breeding biology of Black-faced Sheathbills (Chionis minor) at Marion Island: impacts of cats, mice and climate change? Biological Conservation 92: 299–310.
Jones NV. 1963. The Sheathbill, Chionis alba (Gmelin) at Signy Island, South Orkney Islands. British Antarctic Survey Bulletin 2: 53–71.
McClelland GTW. 2013. Ecology of the Black-faced Sheathbill on Marion Island. PhD Thesis, Stellenbosch University.
McClelland GTW, Altwegg R, van Aarde RJ, Ferreira S, Burger AE, Chown SL. 2018. Climate change leads to increasing population density and impacts of a key island invader. Ecological Applications 28: 212–224.
Parkin DT, Knox AG. 1994. Occurrence patterns of rare passerines in Britain and Ireland. British Birds 87: 585–592.
Shirihai H. 2007. A Complete Guide to Antarctic Wildlife Second Edition. London: A&C Black Publishers Ltd.
Wanless RM, Cooper J, Slabber M, Ryan, PG. 2010. Risk assessment of terrestrially foraging birds on Marion and Gough Islands to primary and secondary poisoning by rodenticides. Wildlife Research 37: 1–7.
Citation
Weideman E, Connan M 2025. Black-faced Sheathbill. In: Lee ATK, Rose S, Banda S, Bezeng SB, Maphalala MI, Maphisa DH, Smit-Robinson H (eds), The 2025 Red Data Book of Birds of South Africa, Lesotho and Eswatini. Johannesburg, South Africa: BirdLife South Africa. Available at: https://www.birdlife.org.za/red-list/black-faced-sheathbill/
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