Justification of Red List Category
This species has not been recorded since the type specimen was collected in 1866, and it was not found during recent surveys since 1998. Very little forest remains within its presumed range and habitat destruction has been extensive and is continuing. However, it cannot be assumed to be Extinct, because there have been some local reports including a recent video that may be of the species, and some Asian scops-owls survive even in degraded habitats. Thus, thorough surveys are required. Any remaining population is likely to be tiny, and for these reasons it is treated as Critically Endangered.
The population is estimated to number fewer than 50 individuals and mature individuals, based on analyses of recent searches and reports, the extent of habitat destruction within its range, and the conclusion that it seems likely that any surviving population will prove minute.
The population is suspected to be stable in the absence of evidence for any declines or substantial threats.
Otus siaoensis is only known from the holotype collected in 1866 on the island of Siau, north of Sulawesi, Indonesia. Given the small size of this island and its generally unvegetated volcanic upper reaches, the original population was probably always modest in size, and any surviving population must be tiny, given that little forest remains. There is some suggestion that the species might survive, on the basis of accounts given by local people; however, a recent survey of nocturnal birds in northern Sulawesi spent 32 days on Siau Island and failed to confirm that the species still occurs there. However, a scops-owl was apparently caught within a building on Siau in December 2017 and a video recorded (T. Nando in litt. 2017): work is ongoing to establish whether this individual can be matched to the holotype of Otus siaoensis. Additionally, semi-structured interviews revealed that small owls do occur on the island and one unidentified call was heard. These reports remain unconfirmed (Hunowi 2006), but a recent sound recording is thought to relate to this species and further searches are planned (N. Brickle in litt. 2007, 2008, 2012). Several further searches in 2009, 2014 and 2015 failed to locate the species, and the origin of an owl-like call recorded in several forest fragments remain uncertain (Sykes 2009).
There are no ecological data, although it is reasonable to assume that the species is a forest dweller, in common with its close congeners. A call thought to relate to this species has been heard in degraded forest on steep slopes (N. Brickle in litt. 2012).
Siau is currently experiencing rapid deforestation. In 1995, there was some lowland forest around Lake Kepetta in the south of the island, but this had been felled by 1998. In August 1998, the island was judged to have been largely converted to mixed plantation and scrub, but small patches of low trees survived. In October 1998, a five-day survey determined that only 50 ha of forest remained, all above 800 m on Gunung Tamata, in the centre of the island.
Conservation Actions Underway
CITES Appendix II. In October 1998, five days were spent on the island of Tagulandang, just south of and almost as large as Siau, but only a few hectares of forest were found to remain, all above 600 m. The Wildlife Conservation Society is providing financial and technical support to PALS, a local NGO from North Sulawesi, to conduct extensive surveys of Siau Island to locate the species. If found, immediate conservation measures will be implemented (N. Brickle in litt. 2007, 2008).
17 cm. Small, forest-dwelling owl. Typical scops-owl with relatively large head and feet, very finely barred wings and tail. Similar spp. The only scops-owl on Siau, however there is the possibility of vagrant Oriental Scops-owl Otus sunia. Voice Undocumented. Taxonomy Previously considered conspecific with Moluccan Scops-owl O. magicus; recent research has shown it to be a valid species on the basis of morphological features.
Text account compilers
Bird, J., Butchart, S., Benstead, P., Derhé, M., Khwaja, N., Martin, R., Symes, A., Tobias, J.
Nando, T., Collar, N., Martin, R., Butchart, S., Ding Li, Y., Brickle, N.
BirdLife International (2020) Species factsheet: Otus siaoensis. Downloaded from http://www.birdlife.org on 23/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/10/2020.