Data Zone
Justification of Red List category
Due to its very small range, occurrence within a single location in respect of the threat from introduced mammals and continuing decline in the area, extent and quality of its habitat, Principe Scops-owl is Critically Endangered. That the species has only been formally described recently prevents the estimation of population trends, however the closely sympatric Principe Thrush Turdus xanthorhynchus is known to be declining with the scops-owl suspected to share the threats to the thrush, especially that from nest predation by the introduced Mona Monkey Cercopitheca mona.
Population justification
The population has been estimated using distance sampling based on point counts detecting calling individuals (assumed to be mature) during the short dry season which is assumed to be the breeding season (Freitas et al. 2022). Two models performed similarly but resulted in distinct estimates, hence both were used resulting in densities of either 33.4 individuals/km2 (95% CI: 23.6-47.2) or 46.4 individuals/km2 (29.3-73.6) and population estimates of 1,149 individuals (813-1,623) or 1,597 individuals (1,007-2,533) (Freitas et al. 2022). It is noted that this estimate is based on the probable occurrence of the species to the highest elevations: if the elevation is restricted to below 500 m Freitas et al. (2022) indicate the population size would be 200 individuals smaller.
Trend justification
There is no data to estimate the population trend, but it is suspected to be declining based on the inferred continuing decline in the area, extent and quality of habitat.
Restricted to native forest on the island of Príncipe, São Tomé and Principe, this has one of the smallest distributions of any owl. All records come from within Príncipe Obô Natural Park in the south of the island with most from lower elevation natural forest, within a range from 62-407 m above sea level (Freitas et al. 2023). The lack of records above 500 m above sea level may indicate that it is genuinely absent from the highest forested parts of the island (Freitas et al. 2022) and the elevation range is here given as 50-500 m. The area of occupancy (AOO) of the species is 64 km2, with the estimated range of 34.4 km2 (Freitas et al. 2022, 2023) falling within 16 2 km x 2 km grid squares. A minimum convex polygon around the distribution in Freitas et al. (2022) is slightly smaller than this, at 55 km2, hence the extent of occurrence (EOO) for the species is matched with the AOO at 64 km2. Both of these values exceed those given in Freitas et al. (2023) due to the latter using a different methodology to that specified in the Red List Guidelines (IUCN 2022). The proposed construction of a dam, ongoing development and small-scale illegal logging, along with the impacts of introduced mammals are inferred to be causing a continuing decline in the area, extent and quality of habitat for the species despite the range being within a protected area (R.F. de Lima in litt. 2022, Freitas et al. 2022). However, there is insufficient evidence to infer a continuing decline in either EOO, AOO or the number of mature individuals given the estimated suitable habitat encompasses the extent of the native forest, which is currently stable, and direct population impacts of introduced mammals are not available.
Principe Scops-owl appears highly dependent on the remaining intact areas of native forest (Freitas et al. 2023). There are some records from mature secondary forests, where these are adjacent to native forest (Freitas et al. 2023). It appears to be more abundant at lower elevations and the highest recorded record is 402 m, despite higher elevations being surveyed (Freitas et al. 2023), suggesting that is associated primarily with lowland tropical moist forest and especially large trees. The area, extent and quality of this habitat is inferred to be declining within the range of the species, despite falling within the Príncipe Obô Natural Park, due to ongoing small-scale illegal logging and clearance for agroforestry, loss to small-scale development and potentially to a larger proposal for the refurbishment and upgrading of a hydro-electric facility along the Papagaio River (R.F. de Lima in litt. 2022, Freitas et al. 2023). It is assumed to be sedentary and to feed on insects (Freitas et al. 2023). It has been found in holes in large trees by parrot trappers and local knowledge suggests that it may displace African Grey Parrots from nest sites (Melo and Dallimer 2009), which are likely to be a limiting resource for both species (Valle et al. 2020).
Principe Scops-owl appears to be associated with large trees and to occur within an adjacent to native forest, hence any loss of intact native forest is likely to impact its population size. Large areas of Principe's forest were cleared for sugar plantations from as early as the 16th century, with these often then converted to other plantations for coconuts or coffee (Jones and Tye 2006). However, recent deforestation is almost non-existent within the Príncipe Obô Natural Park where this species occurs. Since the declaration of the island as a Biosphere Reserve in 2012 the local government promotes the area as a leading example of sustainable development in action and illegal logging is rare (de Lima et al. 2016). However, small areas of the forest are reported to have been lost as a consequence of development within this boundary (Freitas 2019, R. F. de Lima in litt. 2022, Freitas et al. 2023). A particular concern is the proposal for a hydroelectric dam along the Papagaio River (Freitas et al. 2023) which flows northeast through the protected area. The extent of the footprint of the development is unclear, but has the potential to affect a small but significant section of suitable habitat (for approximate location see Anon. 2023).
A number of introduced mammal species are present within the range of the species including Black Rat Rattus rattus, African Civet Civettictis civetta, feral cats Felis catus and Mona Monkey Cercopithecus mona (Fundação Príncipe 2019), with the latter documented to target the nests of Principe Thrush Turdus xanthorhynchus (Guedes et al. 2021) which is assessed as Critically Endangered (BirdLife International 2021) and which overlaps in distribution with Principe Scops-owl (Freitas et al. 2023). The climbing ability of the monkey suggests that the development of nest-raiding is a pervasive threat across the whole range of both these bird species. The Mona Monkey population on Principe was apparently virtually exterminated in the early 20th century, but was present across most of the island by the end of that century and was referred to as vermin in plantations as early as 1958 (Dutton 1994). It is therefore likely, though untested, that the Mona Monkey population in the remote areas of Principe increased in recent decades. While predation has not been demonstrated for nests of Principe Scops-owl, it is plausible from the observed apparent predation of a Principe Thrush nest and predation of experimental nests with quail eggs by Mona Monkeys (Guedes et al. 2021). Black Rats were probably established on Principe around 1500 and quickly became widespread (Dutton 1994), hence although a potential severe nest predator and capable of accessing almost all nests, the scops-owl has persisted alongside rats for over 500 years. If eggs are occasionally taken, it would not seem to be at levels likely to cause significant population declines. There is a theoretical potential threat to the species from feral cats through additional mortality, though there is no evidence for this. Cats have been implicated in the extinction of one owl subspecies, Micrathene whitneyi graysoni from the island of Socorro, but that was in conjunction with severe overgrazing by introduced sheep (Ortiz-Alcaraz et al. 2019). The present species is considered at far lower risk of significant impacts from cat predation within intact native forest, and the opportunity for such predation is probably very limited. The civet is a poor climber and not likely to affect this species.
The abundance of the native Grey Parrot Psittacus erithacus on Principe (Valle et al. 2020) is suggested as a potentially affecting the population size of the species and the two species appear to be each others' main competition for suitable nest holes in the protected area of native forest (Freitas 2019, Freitas et al. 2023). However, existing knowledge of the Otus on Principe is that it is the owl that occupies parrot nesting cavities rather than the other way around (Melo and Dallimer 2009). Reports from those familiar with the birds of the forest prior to the recent formal description of the species relate to scops-owls found in holes being searched for nesting Grey Parrots (Melo and Dallimer 2009). As a natural relationship, there seems little evidence for this representing a direct threat to the species nor of it being modified by human actions to become one.
Conservation and Research Actions Underway
Príncipe was recognised as a UNESCO Biosphere Reserve in 2012, and it appears virtually the entire species range falls within the Príncipe Obo Natural Park. It shares this range with Principe Thrush Turdus xanthorhynchus for which a single species conservation action has been developed: this includes a requirement for population monitoring that has been implemented through transect survey. There are ongoing projects supporting Biodiversity Conservation, Protected Area management, and sustainable management of forests in Sao Tomé and Príncipe, like the ECOFAC6 initiative 2018-2022.
Conservation and Research Actions Proposed
Conduct regular distance sampling surveys to generate population and occupancy trend information for this species as for Principe Thrush. Develop a single species conservation action plan for Otus bikegila, or produce an updated combined species action plan to complement and reinforce conservation actions for Principe's threatened bird species. Monitor nests to evaluate threat posed by Mona Monkey Cercopithicus mona. Investigate the feasibility of reducing densities of Mona Monkey in collaboration with local hunters in core areas of the range of the scops-owl (Freitas et al. 2023). Ensure that proposed development activities conform with the legal protection accorded to the protected area, and lobby to ensure that the maintenance of the existing extent of suitable habitat is a planning consideration in any development that may affect the area.
c. 17-18 cm. A typical small scops-owl and very similar to Sao Tome Scops-owl Otus hartlaubi. Distinguished by voice, which is similar to Sokoke Scops-owl O. ireneae in having short and quite rapidly repeated notes. Occurs in rufous and grey-brown morphs.
Text account compilers
Martin, R.
Contributors
de Lima, R.F.
Recommended citation
BirdLife International (2024) Species factsheet: Principe Scops-owl Otus bikegila. Downloaded from
https://datazone.birdlife.org/species/factsheet/principe-scops-owl-otus-bikegila on 22/12/2024.
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 22/12/2024.