This discussion was first published as part of the 2017 Red List update. At the time a decision regarding the status of several was pended, but to enable potential reassessment of these species as part of the 2018 Red List update this post remains open and the date of posting has been updated.
BirdLife Species factsheet for Nicobar Scops-owl: http://datazone.birdlife.org/species/factsheet/nicobar-scops-owl-otus-alius
Nicobar Scops-owl, Otus alius, is an endemic species of the Nicobar Islands. It is currently listed as Data Deficient on the basis that there had only an extremely limited number of reports of this species; two specimens collected at Campbell Bay, Great Nicobar Island (BirdLife International 2001) and one individual caught and photographed on Teressa Island in 2003 (P. Rasmussen in litt. 2005). This information was insufficient for an accurate evaluation of the species’s Red List status, but now more information regarding this species is available.
Recently, its call has become better known, and has been stated that the species was particularly common on Great Nicobar (P. Singh per Rasmussen and Anderton 2012), and remains so common that people may no longer look for it as a rare/uncommon species to see (S. Dalvi to P. Rasmussen per P. Rasmussen in litt. 2016). Therefore, it may be possible to attempt a population size estimate for Great Nicobar at least. Using high population density estimates for congeners, and assuming only a proportion of its range is occupied would give a population size of 3,200 mature individuals for Great Nicobar. As the species has been found on Teressa Island, it may occur on further islands in the Nicobar group, although some of the more northerly islands have been surveyed and the species not found. Therefore, the global population size may be best placed in the range of 2,500-9,999 mature individuals.
The species is currently considered to be stable as there is currently no evidence for any decline, and there are not any substantial threats. However, forest habitat on Great Nicobar is actually under threat from a range of processes, particularly due to agricultural and settlement expansions, as well as road development projects. The Tsunami of 26th December 2004 also may have impacted upon this species, as not only did it destroy areas of this species’s habitat, but it has also exacerbated the original threats to coastal forest, with the people displaced by the Tsunami clearing areas to build houses and grow crops (K. Sivakumar in litt. 2005). Additionally, the use of pesticides and insecticides within the species’s range may be impacting its food source (S. Pande in litt. 2016), and there may be a low level of direct mortality of individuals as airguns are common and bird trapping does occur (S. Pande in litt. 2016), though the extent to which these practices affect this species is uncertain. When all of these potential threats are taken together, though, it is plausible to infer that the species may be undergoing a slow decline.
Despite having a small estimated population size, which is inferred to be in decline, this species still is likely not to warrant listing as Vulnerable. The rate of decline is unlikely to approach 30% over 3 generations and so would not warrant listing under criterion A. The number of locations* where this species is found is likely >>10, as the main threat is probably habitat loss through low-level deforestation, and so the species would not warrant listing under criterion B or D2. The population size estimate is too large to qualify under criterion D1, and to the best of our knowledge there has been no quantitative assessment of the probability of extinction of this species (criterion E). That leaves only criterion C. Criterion C1 cannot be used in this instance because there has been no direct estimation of the rate of decline. This species also likely does not meet the threshold for Vulnerable under criterion C2 (2,500-9,999 mature individuals where each subpopulation contains fewer than 1,000 mature individuals(i) or all individuals are in 1 subpopulation (ii)). This does depend upon the above population size estimate for Great Nicobar as if this value may be considered too high then the species may approach or meet the threshold for Vulnerable under criterion C2a(i). Therefore, we request any comments or further information regarding the population size estimate for this species, but if it is considered that the above estimate may be appropriate then Nicobar Scops-owl would warrant listing as Least Concern.
*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).
BirdLife International. 2001. Threatened birds of Asia: the BirdLife International Red Data Book. BirdLife International, Cambridge, U.K.
IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. Gland, Switzerland and Cambridge, UK: IUCN Species Survival Commission.
IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN.
Rasmussen, P. C.; Anderton, J. C. Birds of South Asia. The Ripley Guide. Volume 2: Attributes and Status. Second Edition. National Museum of Natural History – Smithsonian Institution, Michigan State University and Lynx Edicions, Washington, D. C., Michigan and Barcelona.