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Giant Ibis Thaumatibis gigantea
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This ibis has an extremely small population, which has undergone an extremely rapid decline as a result of hunting, disturbance and lowland deforestation. It is likely to continue to decline extremely rapidly owing to on-going deforestation and human disturbance. It therefore qualifies as Critically Endangered.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Pseudibis gigantea Sibley and Monroe (1990, 1993), Pseudibis gigantea Collar et al. (1994), Pseudibis gigantea Collar and Andrew (1988)

102-106 cm. Huge, dark ibis. Adult is mostly dark with naked, greyish head and upper neck, dark bands on hindcrown and nape and pale greyish wing-coverts and secondaries with dark cross-bars. Juvenile has short grey feathers on hindcrown and hindneck, lacking the dark bands on hindcrown and nape. Also shorter bill and brown eyes (dark red on adults). Similar spp. White-shouldered Ibis Pseudibis davisoni is smaller and uniformly darker with whitish collar and white patch on inner wing-coverts. Voice Repeated, loud, ringing a-leurk a-leurk at dawn and dusk. Hints Search remote permanent wetlands in dry forests of the lower Mekong basin during the dry season.

Distribution and population
Thaumatibis gigantea is mostly confined to northern Cambodia, where it is probably still fairly widespread but extremely rare; with a few birds from the same population observed in extreme southern Laos (BirdLife International 2001). There is a fairly  recent record from Yok Don National Park, Vietnam (Anon 2003). Its historical range spanned southern Vietnam and south-eastern and peninsular Thailand, where it is now extinct. Available data suggest that it has a patchy distribution across Cambodia (T. Clements et al. in litt. 2007). Some areas of high density exist in the Northern Plains, including Preah Vihear Protected Forest and Kulen Promtep Wildlife Sanctuary (with 30-40 nests monitored annually [T. Evans in litt. 2012) and Western Siem Pang IBA (possibly 40 pairs [H. Wright in litt. 2012]). Other areas appear to have relatively low density populations, which may be clustered in some cases (Lomphat Wildlife Sanctuary, Seima Protection Forest [Bird et al. 2007, WCS/FA 2006], Mondulkiri Protected Forest [T. Gray in litt. per T. Evans] and Phnom Prich Wildlife Sanctuary [Claassen and Ou 2007]) (T. Clements et al. in litt. 2007, T. Clements et al. in prep.). Additional recent records have come from Veunsai proposed Protected Forest in Ratanakiri Province and the first observation south of Tonle Sap Lake since the 1920s was made by camera trap in 2011 (L. Perlman per T. Evans in litt.) Further surveys may confirm other localities in suitable habitat areas such as O Yadao Protected Forest and the unprotected areas west of Phnom Prich Wildlife Sanctuary (T. Evans in litt. 2012). A conservative estimate of the number of breeding pairs at the seven locations is given as 5-10 pairs (T. Evans et al. in litt. 2012).

Population justification
Recent assessment of the available records suggests a minimum estimate of 115 pairs (40 at each of the two high density sites, 5-10 at each of seven low density sites) (T. Evans, H. Rainey, R. Vann and H. Wright in litt. 2012). This is equivalent to a minimum of 230 mature individuals, and roughly 345 individuals in total.

Trend justification
An extremely rapid population decline is suspected to have occurred over the last three generations and is projected to occur over the next three generations, based on information from T. Clements (in litt. 2007), who has commented: "Deforestation scenarios project that Cambodia will lose 50% or more of its forest habitat in the next 25 years, a greater portion of which is expected to be in the lowland areas inhabited by Giant Ibis. For example, recent assessments have shown that Cambodia lost 1-2% of its forest annually during 2002-2006. Giant Ibises are known to be highly sensitive to human disturbance, hence increasing deforestation and habitat fragmentation would have a disproportionate effect on the remaining ibis populations".

Singles, pairs or small parties occur in marshes, pools, wide rivers and seasonal water-meadows in open, predominantly deciduous, dipterocarp lowland forest, although it seems to be dependent on soft mud around seasonal pools (trapaengs). Its diet comprises a variety of invertebrates, crustaceans, eels, small amphibians and reptiles. It frequently feeds in soft mud, but forages on all substrates at trapaengs. It nests in trees, with a preference for large Dipterocarpus (Keo 2008), generally more than 4 km from human habitation (Keo 2008). Females almost always lay two eggs per clutch in the wet season (Keo et al. 2009). Pools and seasonally flooded grassland with earthworm mounds are important in the breeding season, from June to September (Keo 2008). It appears to be largely resident, but apparently wanders widely in response to local disturbance and seasonal water-levels. Generally territorial, the species remains in pairs or small family groups year-round. However, in the dry (non-breeding) season it may be found in small flocks of up to seven individuals or more (H. J. Rainey in litt. 2012).

It has declined as a result of hunting, wetland drainage for agriculture and deforestation. It relies on seasonal pools, which in the past were perhaps maintained by the now much depleted megafauna.  Clearance of very large areas of lowland dry forest, including parts of the Northern Plains (Preah Vihear Protected Forest, Kulen Promtep Wildlife Sanctuary) and other areas (Lomphat Wildlife Sanctuary, Western Siem Pang IBA) where the species occurs, for agro-industry including rubber, cassava, wood pulp and teak plantations, has recently emerged as the greatest threat to this species. Generally the human population is increasing within the range of this species mostly through immigration from other provinces in Cambodia. Subsequent expansion of agricultural land and increasing hunting pressure and disturbance at feeding sites is causing the loss of breeding habitat for the species (An Dara 2008, Clements et al. in prep.). The species appears to be very sensitive to human disturbance (An Dara 2008), particularly during the dry season when both birds and humans are concentrated around available waterholes rendering much apparently suitable habitat unusable. Nest predation by common palm civet Paradoxurus hermaphroditus and/or yellow-throated marten Martes flavigula on two occasions in 2004 suggest that loss of nestlings to mammalian carnivores might be a significant constraint on breeding success (Keo 2008), a theory supported by a study which found that the number of young fledged per nest was 50% higher for protected nests (Keo et al. 2009). A prolonged drought in the 2009-2010 dry season appeared to dramatically lower the breeding success of Giant Ibis, by approximately 50%; climate change may therefore pose a long-term threat to the persistence of this species (H. Rainey in litt. 2012).

Conservation Actions Underway
It occurs at least seasonally in Xe Pian National Biodiversity Conservation Area (NBCA) and Dong Khanthung proposed NBCA, Laos, and Lomphat Wildlife Sanctuary, Preah Vihear Protected Forest and Kulen Prumptep Wildlife Sanctuary in Cambodia. Giant Ibis is depicted on public awareness materials in Laos and Cambodia as part of an on-going campaign to reduce hunting of large waterbirds. A predator-exclusion experiment in 2005-2006 found that nests with predator-exclusion devices (a smooth, hard plastic belt fixed around the base of the nest tree) were more likely to survive than those without (Keo 2008). Most of the protected areas that the species occurs in have ongoing site-based protected area management projects with government and NGOs cooperating to raise funds and implement protection. Ongoing community nest protection activities are taking place in the Northern Plains where local community members are paid to protect Giant Ibis and other waterbird nests. This not only removes a primary threat to the population, but instils local ownership and pride in the charismatic large waterbirds in this landscape. This has stabilised Giant Ibis numbers and increased the populations of other species. Ecotourism projects in the Northern Plains landscape (Tmatboey, O Koki and Prey Veng) and marketing of certified wildlife-friendly agricultural produce ("Ibis Rice") should also benefit this species. 'Giant Ibis Transport' has taken on the role of Species Champion agreeing to provide $51,000 of funding over the next three years.

Conservation Actions Proposed
Improved commitment to conserve protected areas in Cambodia is required by all stakeholders to stabilise the giant ibis population. Advocacy with the Cambodian government to raise the profile of the ecological needs of Cambodia’s national bird will help improve protection of the large undisturbed areas of deciduous dipterocarp forest that this species requires. Conduct further surveys to locate and quantify remaining populations in Laos and Cambodia. Investigate its breeding requirements (including breeding season foraging ecology), demography and seasonal movements. Establish further protected areas encompassing large tracts of habitat found to support populations of the species, including strict protection of suitable permanent wetlands, especially in the dry season. Consolidate and promote further public awareness initiatives to reduce hunting of large waterbirds and wetland disturbance. At key sites, designate some suitable pools as for use only by wildlife. Ensure some pools remain wet during the dry season (e.g. by preventing people from draining them for fishing, and also potentially managing pools to increase their depth) (Keo 2008). Protect and install anti-predator belts on all nest-trees, and protect potential nest-trees (Keo 2008). Monitor the abundance of frogs, eels and mole-crickets in the dry season (Keo 2008), and the impact that local harvesting of frogs may have on prey abundance (H. Wright in litt. 2012). Assess longer-term risk from climate change (T. Evans in litt. 2012).

Related state of the world's birds case studies

An Dara. 2008. Agricultural expansion and its effects on breeding habitat of Giant Ibis Pseudibis gigantea in Kulen Promtep Wildlife Sanctuary, northern Cambodia. MSc Thesis, Tokyo University of Agriculture and Technology, Department of International Environmental and Agricultural Science.

Anon. 2003. Endangered species rediscovered in Yok Don National Park, Dak Lak province. The Babbler: BirdLife in Indochina 2(2): 12-13.

BirdLife International. 2001. Threatened birds of Asia: the BirdLife International Red Data Book. BirdLife International, Cambridge, U.K.

Claassen, A. H.; Ou, R. 2007. A stream and wetland survey of southwestern Phnom Prich Wildlife Sanctuary and adjacent areas, with a focus on large waterbirds. WWF Greater Mekong,Cambodia Country Programme., Phnom Penh.

Keo, O. 2008. Ecology and conservation of the Giant Ibis Thaumatibis gigantea in Cambodia. BirdingASIA 9: 100-106.

Keo, O.; Collar, N. J.; Sutherland, W. J. 2009. Nest protectors provide a cost-effective means of increasing breeding success in Giant Ibis Thaumatibis gigantea. Bird Conservation International 19(1): 77-82.

WCS/FA. 2006. Threatened Species of the Seima Biodiversity Conservation Area. Wildlife Conservation Society - Cambodia Program, and Forestry Administration., Phnom Penh, Cambodia.

Further web sources of information
Detailed species accounts from the Threatened birds of Asia: the BirdLife International Red Data Book (BirdLife International 2001).

Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Benstead, P., Calvert, R., Davidson, P., Mahood, S., Peet, N., Symes, A., Taylor, J., Tobias, J., Martin, R

Buckingham, D., Clements, T., Davidson, P., Duckworth, W., Evans, T., Keo, O., Kim Hout, S., Pollard, E., Rainey, H., Vann, R., Wilson, D., Wright, H.

Recommended citation
BirdLife International (2015) Species factsheet: Thaumatibis gigantea. Downloaded from on 07/10/2015. Recommended citation for factsheets for more than one species: BirdLife International (2015) IUCN Red List for birds. Downloaded from on 07/10/2015.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Giant ibis (Thaumatibis gigantea) 0

Key facts
Current IUCN Red List category Critically Endangered
Family Threskiornithidae (Ibises, Spoonbills)
Species name author (Oustalet, 1877)
Population size 230 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 24,700 km2
Country endemic? No
Links to further information
- Additional Information on this species