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

Justification of Red List category
This species may have a small to moderately small population within its small range, and numbers are almost certainly declining owing to ongoing forest conversion. However, the range is not yet severely fragmented or restricted to few locations, thus the species is classified as Near Threatened.

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.

Ninox rudolfi is restricted to Sumba, Indonesia.

The species occurs up to 1,000 m in primary, disturbed primary and secondary forest and forest edge, in both deciduous and evergreen formations, and mangroves (Olsen et al. 2009, Eaton et al. 2021). It is typically found occurring singly, in pairs or small dispersed groups of up to four birds. Its diet is not known but probably consists mainly of insects.

Ongoing habitat clearance through agricultural expansion and subsistence logging represent the main threats to this species, which is suspected of having lost >5% of suitable habitat between 2012 and 2022 (per Global Forest Watch 2023).

Conservation Actions Underway
CITES Appendix II. Projects in 1989 and 1992 assessed population sizes, status and habitat associations of range-restricted species on Sumba (see Jones et al. 1995) but they failed to document this species in a way that elucidated its population size. It is known (eBird 2023) to occur in Sumba's two terrestrial protected areas documented by UNEP-WCMC and IUCN (2023): Manupeu Tanadaru and Laiwangi Wanggameti. There are efforts (post 2015) to try and reforest some areas of Sumba via agroforestry projects that may benefit this species. For example, the Indigenous Kaliwu Agroforestry System (IKAS) has proven successful locally in planting native species that are congruent with biodiversity conservation objectives and farmers' livelihoods (see Njurumana et al. 2021).

Conservation Actions Proposed
Generate density estimates to inform a revised population estimate for the species. Estimate population trends by calculating rates of forest loss within its range using satellite imagery and remote sensing techniques.
Protect remaining areas of lowland forest. Enforce restrictions on agricultural encroachment and logging within protected areas. Continue and expand agroforestry schemes and monitor their effectiveness for endemic species.

Text account compilers
Berryman, A.

Contributors
Benstead, P., Bird, J., Khwaja, N. & Taylor, J.

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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.