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.
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)
Distribution and population
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.
The species is mostly confined to northern and eastern Cambodia
, where it is probably still fairly widespread but extremely rare; with a few birds from the same population observed in extreme southern Lao PDR
(BirdLife International 2001). It has also been recorded from Yok Don National Park, Viet Nam
(Anon 2003), with the most recent sighting of a single bird in 2011 (Loveridge and Ty 2015). Its historical range spanned southern Viet Nam 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 24 pairs monitored in 2014 [WCS 2014 in Loveridge and Ty 2015]) and Western Siem Pang IBA (where a slight decline has been detected from around 40 pairs [H. Wright in litt.
2012] to 42-62 individuals in 2014 [Loveridge and Ty 2015]). Other areas appear to have relatively low density populations, which may be clustered in some cases: Lomphat Wildlife Sanctuary (approximately 10-15 pairs [Sum and Bou 2012]), Seima Protection Forest (estimated at five pairs [T. Evans, H. Rainey, R. Vann and H. Wright in litt
. 2012 in Loveridge and Ty 2015]) (WCS/FA 2006, Bird et al.
2007), Mondulkiri Protected Forest (anecdotal reports suggest a population of approximately 50 individuals [Gray personal communication in Loveridge and Ty 2015]) (T. Gray in litt.
per T. Evans) and Phnom Prich Wildlife Sanctuary (estimated at five pairs [T. Evans, H. Rainey, R. Vann and H. Wright in litt
. 2012 in Loveridge and Ty 2015]) (Claassen and Ou 2007, T. Clements et al. in litt.
2007, T. Clements et al.
Additional recent records have come from Veunsai proposed Protected Forest in Ratanakiri Province (estimated at five pairs [T. Evans, H. Rainey, R. Vann and H. Wright in litt
. 2012 in Loveridge and Ty 2015]) 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.
, Hance 2012). Further surveys may confirm other localities in suitable areas such as O Ya Dao Protected Forest (although the majority of suitable habitat in this area has now been converted to economic land concessions [Loveridge and Ty 2015]) and the unprotected areas west of Phnom Prich Wildlife Sanctuary (T. Evans in litt.
2012). Owing to large scale habitat loss the species's range is likely to have decreased between 2008 and 2015 (Loveridge and Ty 2015). Population justification
An assessment of the global population was made in 2014 based on newly collected data and expert opinion (including estimates of 48 and 35 mature individuals at the highest density sites) (Loveridge and Ty 2015). The population was estimated at a minimum of 194 mature individuals which is equivalent to approximately 290 individuals.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".Ecology
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) (90% of nesting trees are common deciduous dipterocarp species [Loveridge and Ty 2015]), 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
It has declined as a result of hunting and egg collecting, wetland drainage for agriculture and deforestation. Habitat conversion by large-scale economic land concessions was recently identified as the greatest threat to the species (Loveridge and Ty 2015). 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, Snoul Wildlife Sanctuary, O Ya Dao Protected Forest [Loveridge and Ty 2015]) where the species occurs has already taken place for conversion to agro-industrial uses including rubber, cassava, wood pulp and teak plantations. Small-scale agricultural expansion for subsistence agriculture is also considered a threat (Loveridge and Ty 2015). Generally the human population is increasing within the range of this species mostly through immigration from other provinces in Cambodia, resulting in more infrastructure and development projects that contribute to forest loss. 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.). Construction of new roads through Siem Pang and Seima Protected Forest threaten the species's habitat and potentially expose it to increased disturbance (Loveridge and Ty 2015). Construction of hydroelectric dams in the upper Mekong tributaries (Lower Se San 2 Dam and Lower Sre Pok 2 Dam) could lead to the loss of suitable habitat along the Srepok and Sesan rivers (Loveridge and Ty 2015).
It relies on seasonal pools (trapaengs), which in the past were perhaps maintained by the now much depleted megafauna. The species appears to be very sensitive to human disturbance
(An Dara 2008, Wright et al
. 2012, Ty 2013), particularly during the dry season when both birds and humans are concentrated around available waterholes rendering much apparently suitable habitat unusable. The frequency of burning in deciduous dipterocarp forest has recently increased, potentially having a negative impact on food resources for the species (Loveridge and Ty 2015). Suitable nesting trees may be removed by commercial timber extraction operations or for subsistence housing construction, resulting in the species having to use suboptimal nesting trees (Loveridge and Ty 2015). 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
The species was listed as Critically Endangered in Cambodia by the Ministry of Agriculture, Forestry and Fisheries in 2007 and hunting of the species was prohibited in Cambodia in 1994 (Loveridge and Ty 2015). A 10-year Giant Ibis National Action Plan was published in 2015 (Loveridge and Ty 2015). The plan aims are that by 2025 the Giant Ibis population will be stable or increasing and the species will inhabit a network of well-protected sites. These objectives will be achieved via three channels: 1) protecting key habitat where the species is present; 2) implementing management interventions to increase survival and breeding success; 3) conducting research to inform conservation actions. The delivery of these activities will be monitored by the Ibis Working Group which is currently being established (Loveridge and Ty 2015).
Actions are ongoing to protect the species's breeding and foraging habitats. The Forestry Administration and Ministry of Environment in Cambodia are working to strengthen protected area management at key sites for the species, with support from organisations including Angkor Centre for Conservation of Biodiversity, BirdLife International, Conservation International, Wildlife Conservation Society and the World Wildlife Fund (Loveridge and Ty 2015). 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, Kulen Prumptep Wildlife Sanctuary and Mondulkiri Protected Forest in Cambodia. 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 the species. Restoration of foraging habitats around waterholes is being trialled.
Management to improve breeding success currently involves targeted actions to protect nests and engaging with local communities. 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. Giant Ibis is depicted on public awareness materials in Lao PDR 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). However such devices may alert hunters to the presence of nest sites and should be combined with community engagement work to deter hunting (Loveridge and Ty 2015).
Monitoring is undertaken to assess the effectiveness of actions designed to benefit the species. Reproductive success is assessed through direct monitoring of breeding pairs whilst important populations are surveyed during the dry season (Loveridge and Ty 2015). Changes in forest cover are monitored using remote-sensing techniques (Loveridge and Ty 2015). Following the discovery of an individual in the Kampong Som Valley in Koh Kong Province, Cambodia, Wildlife Alliance plan to survey the area for breeding Giant Ibises (Hance 2012).
'Giant Ibis Transport' took on the role of Species Champion in 2013, agreeing to provide $51,000 of funding over a three year period (Sartori 2013). It was nominated as the national bird of Cambodia in 2005 (Loveridge and Ty 2015). Conservation Actions Proposed
Key actions as identified by the Giant Ibis National Action Plan are: to establish protected areas around key habitat for the species; at the site level, implement conservation actions designed to benefit the species and list the species as a conservation priority at these sites; improve law enforcement; encourage sustainable management of forest resources; provide support to local communities to reduce overexploitation of key habitat for the species (Loveridge and Ty 2015). 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 (particularly undersurveyed areas such as Lomphat Wildlife Sanctuary, Mondulkiri Protected Forest and Mekong Bird Nest Protection site near Kratie [Loveridge and Ty 2015]). 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). Restore foraging habitat. Protect and install anti-predator belts on all nest-trees and work with community groups to deter hunting behaviour (belts around trees may attract hunters to the species's nesting trees) (Loveridge and Ty 2015). 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.
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.
Hance, J. 2012. Giant ibis discovered in new region of Cambodia. The Babbler 40: 16.
IUCN. 2015. The IUCN Red List of Threatened Species. Version 2015-4. Available at: www.iucnredlist.org. (Accessed: 19 November 2015).
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.
Loveridge, R. and Ty, S. 2015. Ten-year species action plan for the Giant Ibis Thaumatibis gigantea in Cambodia. 2015-2025. Phnom Penh, Cambodia.
Sartori, C. 2013. Giant Ibis Transport become first BirdLife Species Champion in Cambodia. BirdLife International. Available at: http://www.birdlife.org/asia/news/giant-ibis-transport-become-first-birdlife-species-champion-cambodia. (Accessed: 07/08/2015).
Sum, P. and Bou, V. 2012. Encouraging Community Involvement in the Conservation of White-shouldered Ibis in Lomphat Wildlife Sanctuary. Final Report to Chicago Board of Trade Endangered Species Fund. BirdLife International Cambodia Programme, Chicago Zoological Society.
Ty, S. 2013. Key factors potentially influencing the occurrence of the critically endangered Giant Ibis Thaumatibis gigantea during the breeding season (April to June) in Western Siem Pang proposed protected forest, Northeast Cambodia. Cambodian Journal of Natural History 2: 121.
WCS/FA. 2006. Threatened Species of the Seima Biodiversity Conservation Area. Wildlife Conservation Society - Cambodia Program, and Forestry Administration., Phnom Penh, Cambodia.
Wright, H.L., Collar, N.J., Lake, I.R., Vorsak, B. and Dolman, P.M. 2012. Foraging ecology of sympatric White-shouldered Ibis Pseudibis davisoni and Giant Ibis Thaumatibis gigantea in northern Cambodia. Forktail 28: 93-100.
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 & Ashpole, J
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.
IUCN Red List evaluators
BirdLife International (2016) Species factsheet: Thaumatibis gigantea. Downloaded from
http://www.birdlife.org on 01/09/2016.
Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from
http://www.birdlife.org on 01/09/2016.
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
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Additional resources for this species