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

Taxonomic note
Rhyticeros cassidix (del Hoyo and Collar 2014) was previously placed in the genus Aceros.

Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	-	A3cd+4cd

Red List history

Year	Category	Criteria
2024	Vulnerable	A3cd+4cd
2016	Vulnerable	A4cd
2012	Vulnerable	A4cd
2009	Least Concern
2008	Least Concern
2004	Least Concern
2000	Lower Risk/Least Concern
1994	Lower Risk/Least Concern
1988	Lower Risk/Least Concern

Migratory status	not a migrant	Forest dependency	high
Land-mass type		Average mass	-

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	432,000 km2	poor
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	unknown	poor	-	-
Population trend	decreasing	poor	suspected	2020-2047
Rate of change over the past 10 years/3 generations (longer of the two periods)	20-29%	-	-	-
Rate of change over the future 10 years/3 generations (longer of the two periods)	20-40%	-	-	-
Rate of change over the past & future 10 years/3 generations (longer of the two periods)	20-40%	-	-	-
Generation length	8.95 years	-	-	-

Population justification: Described as fairly common (Eaton et al. 2021). There have been no surveys to attempt to estimate the global population size of Rhyticeros cassidix. Line transects in April 1993-March 1994 in Tangkoko-DuaSudara Nature Reserve in North Sulawesi yielded a density estimate of 50-85 birds/km² (O'Brien and Kinnaird 1996) but this extremely high density may have been skewed by gatherings at fruiting trees. Non-breeding densities have also been estimated at 51 birds/km², with nesting densities of 10 pairs/km² (Kemp and Boesman 2020). The densities however are tightly linked to food availability, and can range between 9-84 birds/km² (Kinnaird and O'Brien 2007), lending high uncertainty to the average density of the species. No population size is provided due to the high uncertainties in species density over its range, although the large area of suitable habitat and the densities report suggest that the global population size is not small.

Trend justification: R. cassidix is a lowland species, that depends on the prevalence of Ficus spp. (figs) and natural tree cavities for feeding and nesting, respectively (Suryadi et al. 1994, Cahill 2003, Kemp and Boesman 2020). Over half the species’ diet is comprised of figs (Walker 2007), and hornbill populations have been shown to fluctuate over time and space in relation to Fig densities and fruit production, emphasising the importance of conserving preferred feed trees (Kinnaird et al. 1996, Kinnaird and O'Briend 2007). Therefore, forest loss, suspected to be c. 18% over the past three-generations (Global Forest Watch 2024, based on data from Hansen et al. [2013] and methods therein), is likely to underestimate declines in the population where degradation such as selective logging disproportionally removes figs and suitable nesting trees. Over the past three generations therefore, rates of decline are suspected to have been equal to 20-29%. 

Forest loss may be higher in the future. A study by Voigt et al. (2021) projected c. 31% loss of forest cover from 2018 to 2053 (a time-range similar to the 2025-2051 three-generation period), using a dynamic deforestation model that incorporates drivers and patterns of forest loss in Sulawesi. Their study split the region into several sub-regions to calculate sub-regional annual rates of deforestation and is considered more reliable than speculatively projecting the average forest loss rate of the past five-years over the next three-generations (27 years). Additionally, although the Voigt et al. (2021) study included 880 km² of unsuitable mangrove forest in their deforestation rates, this represents only a small fraction of their total (49,570km²) predicted forest loss, and any overestimations of the impact on the species by including mangrove forests is expected to be negligible.
Further, the species is subject to hunting for commercial markets and personal consumptions in Sulawesi (O’Brien and Kinnaird 1996, Kemp and Boesman 2020). Illegal hunting has led to the population declines in R. vigil (Prawiradilaga 2020), and a similar impact would be expected for R. cassidix. Overall future rates of declines are therefore suspected to fall in the range of 20-40%.

Country/Territory	Presence	Origin	Resident	Breeding visitor	Non-breeding visitor	Passage migrant
Indonesia	extant	native	yes

Country/Territory	IBA Name
Indonesia	Lambusango
Indonesia	Popayato - Paguat

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Artificial/Terrestrial	Plantations	suitable	resident
Forest	Subtropical/Tropical Dry	suitable	resident
Forest	Subtropical/Tropical Moist Lowland	major	resident
Forest	Subtropical/Tropical Moist Montane	suitable	resident
Altitude	0 - 1800 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Agriculture & aquaculture	Annual & perennial non-timber crops - Small-holder farming	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Ecosystem degradation, Ecosystem conversion
Biological resource use	Hunting & trapping terrestrial animals - Intentional use (species is the target)	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Reduced reproductive success, Species mortality
Biological resource use	Logging & wood harvesting - Unintentional effects: (large scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Rapid Declines		Medium Impact: 7
		Stresses Species disturbance, Ecosystem degradation, Ecosystem conversion, Reduced reproductive success
Biological resource use	Logging & wood harvesting - Unintentional effects: (subsistence/small scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Species disturbance, Ecosystem degradation, Reduced reproductive success
Energy production & mining	Mining & quarrying	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Species disturbance, Ecosystem degradation
Natural system modifications	Fire & fire suppression - Increase in fire frequency/intensity	Timing		Scope		Severity		Impact
		Past, Likely to Return		Minority (<50%)		Slow, Significant Declines		Past Impact
		Stresses Species disturbance, Ecosystem degradation, Reduced reproductive success

Purpose	Scale
Food - human	subsistence, national
Other household goods	subsistence, national
Pets/display animals, horticulture	international

---

Recommended citation
BirdLife International (2024) Species factsheet: Knobbed Hornbill Rhyticeros cassidix. Downloaded from https://datazone.birdlife.org/species/factsheet/knobbed-hornbill-rhyticeros-cassidix on 23/12/2024.
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 23/12/2024.