Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Partners in Flight Science Committee (2020a) estimated the population in the USA and Canada to be c.150,000 individuals, and the global population to be c.520,000 individuals. The European population is estimated at 312,000-512,000 pairs, which equates to 624,000-1,030,000 mature individuals (BirdLife International In prep.). Europe forms approximately 28% of the global range, so the global population size is suspected to number 2,230,000-3,680,000 mature individuals, although further validation of this estimate is needed.
Trends in North America are not well known as local numbers rise and fall, but several studies suggest an overall decline, often attributed to loss of habitat (Marks et al. 2020). Analysis of results from the Christmas Bird Count suggest a decline of more than 50% since 1970 (Partners in Flight 2020b). In Europe the population size trend is unknown (BirdLife International In prep.).
Declines in Britain are thought to be partly due to the expanding population of Tawny Owl (Strix aluco), competing for space, food and nest sites (Hagemeijer and Blair 1997, Olsen 1999). Agricultural intensification and declining vole populations are also driving declines in Europe (Hagemeijer and Blair 1997, Aschwanden et al. 2005). Locally, threats include pesticide use, persecution and road traffic collisions (König and Weick 2008). Loss of riparian woodlands, grassland and other open habitats to development is considered a threat in the U.S.A. (Olsen 1999). Occasionally shot by bird hunters in Montana and Idaho (Marks et al. 2020).
Conservation actions underway
Listed on CITES Appendix II, Raptors MoU Category 2, the Migratory Bird Treaty Act and Bern Convention Appendix II. Monitored by systematic breeding bird surveys in 14 European countries, constituting 33% of the European countries in which it breeds (Derlink et al. 2018). Covered by the Christmas Bird Count. In Britain, the species has benefited from the provision of artificial nest sites (Garner 1982).
Conservation actions proposed
In the west of its range, suggested management strategies include maintenance of healthy riparian stands, preservation of grassland and marshes, and planting of conifers near open habitats (Marks et al 2020).
Text account compilers
Ashpole, J, Butchart, S. & Ekstrom, J.
BirdLife International (2022) Species factsheet: Asio otus. Downloaded from http://www.birdlife.org on 22/05/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/05/2022.