Great Grey Owl Strix nebulosa


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). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very 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.

Population justification
The global population is estimated to number 120,000 individuals (Partners in Flight 2020), which equates to 80,000 mature individuals. The North American population is estimated at 58,000 individuals (Partners in Flight 2020), or 38,700 mature individuals. The European Population is estimated at 12,400-19,900 mature individuals (BirdLife International in prep.). Europe forms approximately 13% of the global range, so a very preliminary estimate of the global population size is 95,300-153,100 mature individuals, although further validation of this estimate is needed. The population is precautionarily placed in the band 50,000-99,999 mature individuals, but the actual population could be considerably larger.

Trend justification
The overall trend is likely to be increasing. This species has undergone a significant large increase between 1970-2017 in North America (Partners in Flight 2021), and in Europe the population size is estimated to be stable (BirdLife International in prep.).


The species is affected by global warming, which if it persists will continue to move the species’s range northwards (Hagemeijer and Blair 1997). Populations fluctuate in line with vole numbers (Cornulier et al. 2013). Locally, hunting may still be a threat (König 2008). It is also vulnerable to road traffic collisions and loss of habitat from forestry (Holt et al. 1999), although data from Global Forest Watch (2021) suggests that the rate of forest loss over the past three generation lengths (23.64 years [Bird et al. 2020]) has been <15%. Collisions with power lines and cables are also a threat. In North America timber harvesting, collisions with vehicles, strychnine poisoning of pocket gophers, disturbance at foraging habitats due to development of campsites, grazing, peat extraction and agriculture have all been identified as potential threats (Holt et al. 1999). The species is known to be vulnerable to West Nile Virus (Lopes et al. 2007).

Conservation actions

Conservation Actions Underway
This species is listed on CITES Appendix II.


Text account compilers
Clark, J.

Ashpole, J, Butchart, S. & Ekstrom, J.

Recommended citation
BirdLife International (2023) Species factsheet: Strix nebulosa. Downloaded from on 26/09/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 26/09/2023.