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

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
-	-	-

Red List history

Year	Category	Criteria
2023	Near Threatened	B1b(ii,iii); C2a(ii)
2016	Near Threatened	B1ab(ii,iii,v);C1+2a(ii)
2012	Near Threatened	B1ab(ii,iii,v);C1+2a(ii)
2008	Near Threatened	B1a+b(iii); C1; C2a(ii)
2004	Near Threatened
2000	Lower Risk/Near Threatened
1996	Vulnerable
1994	Vulnerable
1988	Lower Risk/Least Concern

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

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	13,100 km2	medium
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	5000-24000, 5000-15000 mature individuals	poor	inferred	2022
Population trend	decreasing	-	suspected	2012-2029
Rate of change over the past 10 years/3 generations (longer of the two periods)	1-9%	-	-	-
Rate of change over the future 10 years/3 generations (longer of the two periods)	1-9%	-	-	-
Rate of change over the past & future 10 years/3 generations (longer of the two periods)	1-9%	-	-	-
Generation length	5.8 years	-	-	-
Number of subpopulations	1	-	-	-
Percentage of mature individuals in largest subpopulation	100%	-	-	-

Population justification: The population size of this species has never been formally estimated, although it is described as 'uncommon' by Eaton et al. (2021). Citizen science data (eBird 2023) suggest it is found in most forest blocks that have been searched and is considered here to be a widespread bird on Sumba. Remote sensing data indicate that c.2,000 km² of forest remains on Sumba (per Global Forest Watch 2023), and most of this is suspected to be occupied given this species' apparent tolerance of degradation (Olsen et al. 2009, Eaton et al. 2021). Few robust densities for Ninox owls are available, although Jakosalem et al. (2013) recorded densities of up to 20 mature individuals/km² for Ninox rumseyi of Cebu. However, these data were based on home ranges from satellite-tracking that the authors acknowledged yielded territory sizes that were probably too small due to the short time the birds were followed for. The estimated home ranges were, for example, up to ten times smaller than that of Ninox boobook sensu stricto (Olsen et al. 2011). Inferring a density of 5-15 mature individuals/km², and an occupancy of 50-80%, the population size of Ninox rudolfi is inferred to be 5,000-24,000 mature individuals, with a precautionary best estimate of 5,000-15,000.

Trend justification: The only identified threat to this species is habitat loss and degradation. In the three generations (17.3 years; Bird et al. 2020) to 2022, forest cover on Sumba declined by c.6% (Global Forest Watch 2023, based on data from Hansen et al. [2013] and methods disclosed therein). This species is tolerant of edge habitat and degraded forest (Olsen et al. 2009) and therefore may not be declining directly in line with forest cover loss. Alternatively, rates of population decline may be slightly faster than forest cover loss alone, on the basis that the species requires larger trees for nesting. Given these uncertainties, the population is tentatively suspected to be declining at a rate of 1-9% over three generations.

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

Country/Territory	IBA Name
Indonesia	Laiwanggi Wanggameti
Indonesia	Manupeu Tanadaru
Indonesia	Poronumbu

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Artificial/Terrestrial	Subtropical/Tropical Heavily Degraded Former Forest	suitable	resident
Forest	Subtropical/Tropical Dry	major	resident
Forest	Subtropical/Tropical Mangrove Vegetation Above High Tide Level	major	resident
Forest	Subtropical/Tropical Moist Lowland	major	resident
Altitude	0 - 1000 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Agriculture & aquaculture	Annual & perennial non-timber crops - Agro-industry farming	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Ecosystem degradation, Ecosystem conversion
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	Logging & wood harvesting - Unintentional effects: (large scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Ecosystem degradation, Ecosystem conversion

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Recommended citation
BirdLife International (2024) Species factsheet: Sumba Boobook Ninox rudolfi. Downloaded from https://datazone.birdlife.org/species/factsheet/sumba-boobook-ninox-rudolfi 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.