• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category
Sumba Hornbill has been assessed as Endangered because it has a small declining population, with very rapid population reductions suspected to be ongoing owing to rapid habitat loss from selective logging, deforestation and degradation from clearance including through the use of fires. In particular, the loss and degradation of large (<10km²) forest patches, and removal of suitable nesting trees from within apparently suitable areas, appear to be severely impacting the species. 

Population justification
Recent population estimates indicate that there has been a rapid decline in the population over the past three generations, and it appears that extrapolations from high densities from a short survey of Manupeu-Tandaru National Park were inappropriate, and the estimate of 6,400 (D. Mulyawati in litt. 2010) is considered an overestimate (T. O'Brien in litt. 2020). The most recent population estimate is of 1,650 mature individuals, based on the reduction in extent and number of large forest patches. With a rapid suspected population reduction underway and an inferred continuing decline in mature individuals the current population size is estimated to be between 1,000-2,000 mature individuals.

Trend justification
Despite the adequate protection of an area of lowland forest in the Manupeu-Tanadaru National Park (D. Mulyawati in litt. 2010), an overall population decline of 30-49% is estimated owing to the extensive and on-going loss and fragmentation of forest habitats outside of the reserve.

This species is endemic to the island of Sumba, Nusa Tenggara, Indonesia. 33 forest patches scattered across the island were surveyed in the 1990s (O'Brien et al. 1998) and while the species would use small patches for foraging, it was only consistently present in patches over 1,000 ha, of which there were 17 at the time. This fieldwork produced a population estimate of 3,926 (3,475-4,377 mature individuals based on a density of 2.3 hornbills/km², and an estimated 1,732 km² total forest-cover) (O'Brien et al. 1998). Several of the larger forest patches have since been considerably reduced in size by deforestation (Global Forest Watch 2020) and an updated population estimate in 2010 was only 1,650 mature individuals (T. O'Brien in litt. 2010). 

An estimate from distance sampling of 6,400 from Manupeu-Tanadaru National Park (D. Mulyawati in litt. 2010) alone is considered an overestimate, likely due to the impact of the patchy occurrence of flocks of the species in this protected area (T. O'Brien in litt. 2020).

Despite frequenting a variety of forested habitats, it shows a strong association with low altitude semi-evergreen forest containing large trees with a dense canopy. It is rare or absent in patches <10 km², and may only use them if they are within ranging distance of larger fragments (O'Brien et al. 1998,  Sitompul et al. 2004). It has been recorded up to at least 950 m, at forest edges and in isolated trees or groves in parkland far from closed forest, although its occurrence in parkland may be limited to very infrequent dispersal movements. Nest-cavities tend to be situated within evergreen forest in the trunks of large deciduous trees, especially Tetrameles nudiflora, a species that is important for other threatened species on the island (e.g. Sulphur-crested Cockatoo Cacatua sulphurea and Sumba Eclectus Eclectus cornelia) (BirdLife International 2001).

Habitat destruction and fragmentation stemming from small-scale logging, fuelwood collection and clearance for cultivation or pasture poses the main threat. In particular, this species appears very badly affected by the reduction in size of larger patches, as the species appears unable to persist in patches below 10 km². These pressures are exacerbated by fire resulting from a dry climate and uncontrolled burning to encourage new growth for cattle. Since the 19th century, c. 60% of forest has been lost. Selective logging for construction may be having a severe impact due to intense competition for nesting sites among the remaining populations of hole-nesting forest birds on Sumba,  potentially severely impacting reproductive output in what may appear large and suitable forest patches (Reuleaux 2017, M. Halouate in litt. 2020). A preference for lowland areas further compounds the threat of habitat loss, as would previously reported minor impacts of trade (not considered to be a significant threat any more) and exploitation for food (BirdLife International 2001). Although one large area of lowland forest appears to be well protected in the Manupeu-Tanadaru National Park (D. Mulyawati in litt. 2010), forest loss continues in many other forest patches and around the edges of protected areas (Global Forest Watch 2020).

Conservation Actions Underway
CITES Appendix II. Populations occur in the recently established Manupeu-Tanahdaru National Park (MTNP) and Laiwangi-Wanggameti National Park (LWNP) (1,350 km² combined), which are now monitored by government-run management authorities set up in 2006. Burung Indonesia has been working intensively since 2002/2003 on strengthening Sumba's national park management. The project included facilitating local communities and government to develop village conservation agreement and to agree on the demarcation of the MTNP, resulting a reduced external pressure on illegal logging, forest destruction, and better law enforcement (A. Dian in litt. 2009). Population surveys were carried out for the species in the MTNP in 2009 (D. Mulyawati in litt. 2010). The illegal wildlife trade has been monitored since 2004, and in four big cities in Sumba there have been no cases of the species being recorded in trade/captivity (D. Mulyawati in litt. 2010, M. Kinnaird in litt. 2016).

Conservation Actions Proposed
Conduct detailed research into the breeding and foraging ecology of the species. Conduct an accurate population survey across the entire island and implement a monitoring programme to establish population trends. Gazette strict nature reserves at Yawila, Puronumbu and Luku Melolo, a wildlife sanctuary at Lulundilo and a forest park at Tanjung Ngunju. Support initiatives to establish and manage further protected areas. Continue to work with local communities to prevent lowland forest clearing, hunting and trapping.

Identification

70 cm. Medium-sized, dark, forest-dwelling hornbill. Male blackish apart from dark rufous crown and nape, paler and buffier on throat. Large yellowish bill with serrated casque and red patch at base. Plumage of female entirely black. Voice Harsh clucking notes, short erm-err and cackling kokokokoko.

Acknowledgements

Text account compilers
Patil, I., Datta, A., Martin, R.

Contributors
Dian, A., Gonzalez, J., Halaouate, M., Kinnaird, M., Mulyawati, D., O'Brien, T., Taylor, J. & Westrip, J.R.S.

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Recommended citation
BirdLife International (2024) Species factsheet: Sumba Hornbill Rhyticeros everetti. Downloaded from https://datazone.birdlife.org/species/factsheet/sumba-hornbill-rhyticeros-everetti on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 22/11/2024.