Justification of Red List Category
This species is listed as Endangered because it has an extremely small population, which is probably stable. Its population size and very small range on one island make it susceptible to stochastic events, such as extreme weather events and the introduction of alien taxa.
Currie et al. (2004a) estimated 125-142 territories (i.e. possibly 250-284 mature individuals) in 2001/2002 based on modelling altitude and habitat suitability. Given the uncertainty in these extrapolations and the time since the surveys it is plausible that the population now falls below 250 mature individuals, hence the range 249-300 mature individuals is used here.
There is no data on the current population trend (D. Currie in litt. 2004; R. Fanchette in litt. 2005), but it is suspected to be stable, since most available habitat is occupied and the area of habitat is probably stable (R. Bristol in litt. 2005), with a reduction reported at the lower limits of the species's range (e.g. La Misère), mainly owing to housing development (G. Rocamora in litt. 2007).
Otus insularis is endemic to Mahé in the Seychelles. The population size was previously estimated at 90-180 pairs (Rocamora 1997; Watson 2000b). However, modelling according to altitude and vegetation (thus excluding unsuitable habitat) produced an estimate of 125-142 territories, or 250-284 mature individuals, in a c.31 km2 range (Currie et al. 2004a). There are no data on the current population trend (Safford and Rocamora 2013; R. Fanchette in litt. 2005; D. Currie in litt. 2004). However, it is highly unlikely to be undergoing significant declines, since most available habitat is occupied and the area of habitat is probably stable (R. Bristol in litt. 2005). The population may have been more or less stable since the mid-1970s (Rocamora 1997; Watson 2000b). Eight of 12 sites where pairs were regularly seen in 1975-1976 were visited again in 1993 and pairs were detected at all eight sites (Watson 2000). However, some sites that used to be occupied on the borders of the Morne Seychellois National Park appear to have now been deserted, probably due to residential encroachment and / or human disturbance (Safford and Rocamora 2013).
It favours upland (>400 m) mixed forest with native and introduced tree species and a high canopy, which is often mist-shrouded, and generally in areas of high rainfall (Rocamora 1997; Currie et al. 2004a), in valleys and on sheltered slopes. It also may be found in the vicinity of tea plantations and residential areas near forest (Rocamora 1997). The species's increased frequency at higher elevations may be associated with a preference for less-disturbed forest that as a result is dominated by native tree species, although it is found in forested areas in close proximity to urban and agricultural areas (Currie et al. 2004a). Between 250 and 600 m it inhabits secondary forest, which is dominated by exotics (Mellanby et al. 1996). It has been recorded above 700 m and suitable habitat exists up to the summit of Morne Seychellois at 906 m (D. Currie in litt. 2012). Its previously supposed association with 'boulder fields' is probably ecologically meaningless because of the ubiquitous nature of such terrain (Currie et al. 2004a; Currie et al. 2002). Territories are c.20-25 ha (Currie et al. 2004a). It has been observed from low in the understorey up to the lower canopy (Mellanby et al. 1996). Main prey items discovered from pellet analysis were Orthoptera, Coleoptera and Araneae, and vertebrates may be taken (Currie et al. 2002). Similarly, during observations at two nests, the majority of items fed to nestlings were invertebrates, mostly Orthoptera, arachnids and Lepidoptera (Currie et al. 2003). These observations on the species's diet suggest that it forages on foliage and tree trunks, not just on the ground (Currie et al. 2003). Nests are found within wooded areas, which are made up mainly of exotic vegetation (Fanchette et al. 2000). Eight nests have been found by scientists, all in the cavities of two relatively uncommon tree species, the native Dillenia ferruginea and introduced Pterocarpus indicus, at heights of 7-25 m (Currie et al. 2002; Currie et al. 2004b). P. indicus may have become important in the life history of the species if it replaced native trees that had originally provided important nest-sites J. A. Mortimer in litt. 2005). Nests are usually found in live trees located amongst dense vegetation (R. Fanchette in litt. 2005). A single egg is laid; congeners normally lay two, but Seychelles land birds characteristically lay a single egg (Watson 1978, Currie et al. 2002, Currie et al. 2004b). Observations at two nests revealed that incubation lasted for 3-4 weeks and the fledging period was 4-6 weeks (Currie et al. 2004b). The species can probably breed year-round with peaks in nesting around May and October (Watson 2000, Currie et al. 2004b). Pairs can initiate re-nesting soon after nest failure (Currie et al. 2002; Currie et al. 2004b). Breeding success is recorded as low at c.0.5 fledglings/territory/year (Currie et al. 2002; Currie et al. 2004b), although this may be high enough to maintain population stability (D. Currie in litt. 2007).
Some lowland habitat destruction, at the lower limit of the species's range, is occurring due to housing and other developments (Rocamora 1997, G. Rocamora in litt. 2007, N. Doak in litt. 2007), which may have resulted in the abandonment of some territories (Safford and Rocamora 2013). However, highland forest on Mahé that was being cleared on a small scale for timber and tea cultivation (Rocamora 1997, A. Skerrett in litt. 1999), no longer is (G. Rocamora in litt. 2016). Forest clearance was extensive in the 19th and 20th centuries, but such rates unlikely to occur again (D. Currie in litt. 2007). Presently, localised forest clearance, e.g. for cinnamon Cinnamomum verum coppicing and governmentral forestry activities may impact specific pairs (D. Currie in litt. 2007), for example localised forestry activity is thought to have caused the desertion of one nest and the shifting of several pairs by over 300 m (Currie et al. 2004b). If areas south of the national park were opened up to development the species could suffer a severe reduction in population size (G. Rocamora in litt. 2007). Promotion of ecotourism in the uplands, resulting in the creation of new trails and increased disturbance, may be a localised threat (N. J. Shah in litt. 2000). Introduced species including rats, cats and Barn Owls Tyto alba are likely predators of nests and adults (Rocamora 1997, A. Skerrett in litt. 1999, Currie et al. 2004b, A. Skerrett in litt. 1999). Black rats Rattus rattus are very likely to have predated two or three of the few nests so far discovered for this species (Fanchette et al. 2000, Currie et al. 2002, Currie et al. 2004b). The Common Mynah Acridotheres tristis is a potential nest-site competitor (Currie et al. 2004b). Rattus rattus and A. tristis both occur at high densities on Mahé, and T. alba is often present in O. insularis territories (Currie et al. 2004b). The impact of introduced species on the breeding success of O. insularis is unknown (Currie et al. 2004b). Cinnamon significantly encroaches habitat, but effects on the species are unknown (N. Doak in litt. 2007). Over recent years, P. indicus has been decimated by a fungal disease and has suffered widespread local extinction on Mahé, resulting in a drastic reduction in suitable nest-sites (P. Matyot in litt. 2005; G. Rocamora in litt. 2007). Climate change presents a long-term threat to the species (R. Fanchette in litt. 2005), probably through increases in extreme weather events (G. Rocamora in litt. 2007). Storms might cause damage to Albizia-dominated forest, as it is prone to wind damage (D. Currie in litt. 2007). The existence of only one island population leaves this species vulnerable to catastrophic events such as the introduction of a novel predator or disease (D. Currie in litt. 2007, G. Rocamora in litt. 2007).
Conservation Actions Underway
CITES Appendix II. The species is protected by law in Seychelles under the Animals and Bird Protection Act (Currie et al. 2002). Much of the highland forest where the species occurs is incorporated into the Morne Seychellois National Park (MSNP), although the park covers only c.55% of the species's maximum predicted range (Currie et al. 2004a). A second protected area of 1,000 ha, south of the MSNP, proposed in 2000-2001, would increase the protection of the species's range to 80% (Currie et al. 2002; Currie et al. 2004a; D. Currie in litt. 2007). Some other sites are also classified as Sensitive Areas under the Environment Protection Act (S. Parr and N. J. Shah in litt. 1999). A stakeholder agreed action plan highlighted key conservation management priorities for this species (Currie et al. 2002). Importantly, there appears to be few realistic options for increasing its range on Mahé and few options for translocation programmes, given that the most suitable island (Silhouette) may hold only 20 territories (based on the Mahé model) and similarly hosts a suite of alien predators (Currie et al. 2002; Currie et al. 2004a).
20-22 cm. Small, eared owl. Only one colour form: greyish-brown with rufous on underparts and around facial disc. Heavily barred, streaked and vermiculated. Unfeathered tarsi and toes. Eyes large, bright yellow to orange-red. Voice Loud, far-carrying, rasping, continuous waugh waugh and various tok tok notes. Hints Best located by call at dusk or dawn.
Text account compilers
Ekstrom, J., Pilgrim, J., Shutes, S., Symes, A., Taylor, J., Warren, B. & Westrip, J.
Bristol, R., Currie, D., Doak, N., Lucking, R., Parr, S., Rocamora, G., Shah, N. & Skerrett, A.
BirdLife International (2020) Species factsheet: Otus insularis. Downloaded from http://www.birdlife.org on 16/02/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/02/2020.