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Tooth-billed Pigeon Didunculus strigirostris
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Justification
This species has been uplisted from Endangered because its population is estimated to be smaller than previously thought. It is now listed as Critically Endangered because it is estimated to have an extremely small population that is inferred to be in decline owing to the interacting threats of human-driven habitat loss, habitat damage caused by cyclones, invasive species and non-target mortality caused by hunters. There is now an urgent need for intensive conservation actions to halt the species's perilous slide towards extinction. 

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.

Identification
31 cm. Chunky, dark pigeon with heavy, hooked bill. Lower mandible has two "teeth" that overlap the upper. Mostly greenish-black with chestnut upperparts. Bill red at base, then yellow. Red eye-ring. Similar spp. Metallic Pigeon Columba vitiensis and Pacific Imperial-pigeon Ducula pacifica slimmer and longer tailed with no chestnut on upperparts. Voice Uniform territorial coo, higher-pitched in female. Irregular, frequent repetitions (Beichle 1991). Hints Prefers to stand on thick branches in dark interior of tree-crowns, often 15-20 m high, but up to 40 m (Beichle 1982).

Distribution and population
Didunculus strigirostris is endemic to Samoa, where it is known as Manumea. Its total population was estimated at 4,800-7,200 birds in the mid-1980s (Beichle 1987), but in the 1990s the population showed a drastic decline owing to the effects of cyclones such that, in 2000, fewer than 2,500 mature individuals were believed to survive. In 1999 and 2000, surveys on Savai'i showed that it had become rare with pairs scattered in suitable habitat. Concern was raised that these small, increasingly fragmented sub-populations may not be viable (H. Freifeld in litt. 1999). An eleven-month survey in 2005-2006 reported the species from only ten locations, and the population was estimated to number only a few hundred, although the remote and largely intact uplands of Savai'i remained largely unsurveyed (Ministry of Natural Resources and the Environment, Samoa 2006). Small numbers were recorded in a few locations on Upolu in 2009, but a lack of recent sightings among local hunters further suggests that declines are continuing (M. O'Brien in litt. 2011, R. Stirnemann in litt. 2011). A single individual on Nu'utele in 2010 may have been an immigrant from Upolu (M. O'Brien in litt. 2011). Surveys for the species conducted by the Ministry of Natural Resources and the Environment on Savai'i in 2013 yielded only one record, of a juvenile bird that was photographed, this being the first confirmed sighting on Savai'i for almost a decade, although there was an additional, unverified sighting in 2012 (BirdLife International 2014). Over a thousand hours of sound recordings using remotely located microphones had not yet been analysed as of early 2013 (Ministry of Natural Resources and the Environment, Samoa in litt. 2013). If numbers on Savai'i have declined as steeply as appears to be the case on Upolu, it is thought likely that the total population numbers fewer than 250 birds (M. O'Brien in litt. 2011). The population is therefore estimated to number fewer than 250 mature individuals, with no more than 50 mature individuals in each sub-population.

Population justification
The population was previously estimated to number 1,000-2,499 individuals (U. Beichle in litt. 2000); however, the low number of recent records and lack of sightings by local people strongly suggest that the population is now extremely small, thus it is placed in the band for 50-249 mature individuals, assumed to equate to c.70-380 individuals in total. It is estimated that there are no more than 50 mature individuals in each of the two presumed sub-populations, on Upolu and Savai'i.

Trend justification
No new data are available on population trends, but the species is suspected to have undergone a very rapid decline over the past three generations (estimated at 20 years), based on the low number of recent records, and owing to the partially synergistic effects of forest degradation by cyclones and invasive tree species, as well as accidental mortality from hunting and direct loss of habitat through agricultural expansion. This assessment of the rate of decline may be conservative given the perceived change in abundance since the 1990s and the potential impacts of Severe Tropical Cyclone Evan in December 2012 (R. Stirnemann in litt. 2012). It is suspected that a very rapid decline will take place over the next three generations if conservation actions are not increased, owing to the expected impacts of intermittent powerful cyclones and the inherent consequences of the species's extremely small population size.

Ecology
It occurs in primary forest from sea-level to 1,600 m, also occurring in forest edge, along forest roads and sometimes visiting clearings where native trees remain (Beichle 1987, Blockstein 1987, U. Beichle in litt. 2000). It is specialised to feed on the seeds of Dysoxylum spp. (using its unusual bill to saw through the tough, fibrous pericarp), also feeding on other fleshy fruit (Beichle 1987). Its clutch-size is probably two (Beichle 1987).

Threats
It is threatened by deforestation for agriculture, and also the severe effects of cyclones, e.g. in 1990 and 1991, when canopy cover was reduced from 100% to 27% (Elmqvist et al. 1994) and up to 95% of large trees may have been lost in some areas (D. Scott in litt. 2012), and more recently when cyclones passed close to the islands (J. Atherton in litt. 2007). Severe Tropical Cyclone Evan in December 2012 is thought likely to have further impacted the species's population, as large numbers of native trees were felled by the storm (R. Stirnemann in litt. 2012). Forest quality is further reduced by the subsequent invasion of highly aggressive non-native trees (H. Freifeld in litt. 1999). Hunting is also a further threat, e.g. in 1985, 400 birds were being shot every year (Beichle and Maelzer 1985). Although hunting is now illegal, birds are still shot in the seasonal harvest of unprotected pigeon species (Blockstein 1987). Predation of eggs and nestlings by Pacific rats Rattus exulans and cats represents a potential threat that may have been underestimated (Ministry of Natural Resources and the Environment, Samoa in litt. 2013).

Conservation Actions Underway
It is fully protected by law and hunting is banned, although this has not been enforced. It occurs in some proposed and a few existing protected areas, but these have suffered cyclone damage and the O Le Pupu Pu'e National Park on Upolu is threatened by logging and cattle-farming (Beichle and Maelzer 1985). It has been chosen as a flagship species to promote conservation awareness, and was selected as the mascot of the South Pacific Games held in 2007 in Samoa, in order to promote bird and forest conservation. A species recovery plan was published by the Samoan Ministry of Natural Resources and Environment and funds have since been sought to implement the plan. Communities were being visited in 2013 to survey for sightings by local people and raise awareness of the species, potentially reducing hunting and increasing the chances of future sightings (Ministry of Natural Resources and the Environment, Samoa in litt. 2013). Discussions have taken place between the Samoan Ministry of Natural Resources and Environment and zoological societies on the possibility of establishing a captive rearing facility in Apia (Ministry of Natural Resources and the Environment, Samoa in litt. 2013).Conservation Actions Proposed
Continue to carry out surveys, with the participation of local communities, to quantify the remaining population and locate any strongholds. Investigate the species's ecology and life history, including its habitat requirements (Freifeld 1999, SPREP 1999, U. Beichle in litt. 2000). Study the impacts of introduced predators. Carry out habitat restoration to increase the species's resilience to future cyclones. Increase the area of suitable habitat that receives effective protection. Extend the hunting ban to cover all native columbids to avoid "mistaken" shooting (U. Beichle in litt. 2000). Conduct further awareness-raising activities to reduce mortality from hunting activities. Consider establishing a captive population, and, in due course, consider translocations to islands such as the rat-free Nu'utele if these are found to be suitable.

References
Beichle, U. 1982. Untersuchungen zur Biologie und Systematik der Zahntaube Didunculus strigirostris (Jardine 1845). dissertation. Doctoral, Kiel:Christian-Albrechts Universitat.

Beichle, U. 1987. Lebensraum, Bestand und Nahrungsaufnahme der Zahntaube, Didunculus strigirostris. Journal für Ornithologie 128: 75-89.

Beichle, U. 1991. Status and acoustical demarcation of pigeons of Western Samoa. Notornis 38: 81-86.

Beichle, U. 2006. Saving Samoa’s Critically Endangered Maomao and Manumea: Final Report.

Beichle, U. and Baumann, S. 2003. Die Landvoegel der Samoa-Inseln. TenDenZen 1-2: 1-156.

Beichle, U.; Maelzer, M. 1985. A conservation programme for Western Samoa. In: Diamond, A.W.; Lovejoy, T.E. (ed.), Conservation of tropical forest birds, pp. 297-299. International Council for Bird Preservation, Cambridge, U.K.

Blockstein, D. E. 1987. Preliminary report on the ecology and status of the Tooth-billed Pigeon or "Manumea" (Didunculus strigirostris) in Western Samoa.

Elmqvist, T.; Rainey, W. E.; Pierson, E. D.; Cox, P. A. 1994. Effects of tropical cyclones Ofa and Val on the structure of a Samoan lowland rain forest. Biotropica 26: 384-391.

Freifeld, H. 1999. Samoa bird studies - preliminary ideas for O Le Siosiomaga Society, Inc..

IUCN. 2013. IUCN Red List of Threatened Species (ver. 2013.2). Available at: http://www.iucnredlist.org. (Accessed: 13 November 2013).

Ministry of Natural Resources & Environment (MNRE). 2006. Recovery plan for the Manumea or Tooth-billed Pigeon Didunculus strigirostris.

SPREP. 1999. Proceedings of the Polynesian Avifauna Conservation Workshop held in Rarotonga, 26-30 April 1999.

Further web sources of information
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., Mahood, S., O'Brien, A., Shutes, S., Stattersfield, A., Symes, A. & Taylor, J.

Contributors
Atherton, J., Beichle, U., Freifeld, H., Hobcroft, D., O'Brien, M., Scott, D. & Stirnemann, R.

Recommended citation
BirdLife International (2014) Species factsheet: Didunculus strigirostris. Downloaded from http://www.birdlife.org on 25/12/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/12/2014.

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.

Key facts
Current IUCN Red List category Critically Endangered
Family Columbidae (Pigeons, Doves)
Species name author (Jardine, 1845)
Population size 50-249 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) -
Country endemic? Yes
Links to further information
- Additional Information on this species