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Great Grey Owl Strix nebulosa

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 fluctuating, 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.

Taxonomic source(s)
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: # _the_WP15.xls#.
Cramp, S.; Perrins, C. M. 1977-1994. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic. Oxford University Press, Oxford.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Population justification
The global population is estimated to number approximately 190,000 individuals which equates to 127,000 mature individuals (Partners in Flight Science Committee 2013). The North American population is estimated at 90,000 individuals or 60,000 mature individuals (Partners in Flight Science Committee 2013). The European population is estimated at 1,900-7,500 pairs, which equates to 3,900-15,000 mature individuals (BirdLife International 2015). Europe forms approximately 13% of the global range, so a very preliminary estimate of the global population size is 30,000-115,000 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 large and statistically significant increase over the last 40 years in North America (4900% increase over 40 years, equating to a 166% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Note, however, that these surveys cover less than 50% of the species's range in North America. In Europe the population size is also estimated to be increasing (BirdLife International 2015).

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). 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).

BirdLife International. 2015. European Red List of Birds. Office for Official Publications of the European Communities, Luxembourg.

Cornulier, T., Yoccoz, N.G., Bretagnolle, V., Brommer, J.E., Butet, A., Ecke, F., Elston, D.A., Framstad, E., Henttonen, H., Hörnfeldt, B., Huitu, O., Imholt, C., Ims, R.A., Jacob, J., Jędrzejewska, B., Millon, A., Petty, S.J., Pietiäinen, H., Tkaadlec, E., Zub, K. and Lambin, X. 2013. Europe-wide dampening of population cycles in keystone herbivores. Science 340(6128): 63-66.

Hagemeijer, E.J.M. and Blair, M.J. 1997. The EBCC atlas of European breeding birds: their distribution and abundance. T. and A. D. Poyser, London.

Holt, D.W., Berkley, R., Deppe, C., Enríquez Rocha, P., Petersen, J.L., Rangel Salazar, J.L., Segars, K.P. and Wood, K.L. 1999. Great Grey Owl (Strix nebulosa). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. and de Juana, E. (eds), Handbook of the Birds of the World Alive, Lynx Edicions, Barcelona.

IUCN. 2015. The IUCN Red List of Threatened Species. Version 2015-4. Available at: (Accessed: 19 November 2015).

König, C. and Weick, F. 2008. Owls of the World. Christopher Helm, London.

Lopes, H., Redig, P., Glaser, A., Armien, A. and Wünschmann, A. 2007. Clinical Findings, Lesions, and Viral Antigen Distribution in Great Gray Owls (Strix nebulosa) and Barred Owls (Strix varia) with Spontaneous West Nile Virus Infection. Avian Diseases 51(1): 140-145.

Partners in Flight Science Committee. 2013. Population Estimates Database, version 2013. Available at: (Accessed: 09/07/2015).

Further web sources of information
Detailed regional assessment and species account from the European Red List of Birds (BirdLife International, 2015)

Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)

Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Butchart, S., Ekstrom, J. & Ashpole, J

IUCN Red List evaluators
Butchart, S. & Symes, A.

Recommended citation
BirdLife International (2015) Species factsheet: Strix nebulosa. Downloaded from on 29/11/2015. Recommended citation for factsheets for more than one species: BirdLife International (2015) IUCN Red List for birds. Downloaded from on 29/11/2015.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Great grey owl (Strix nebulosa) 0

Key facts
Current IUCN Red List category Least Concern
Family Strigidae (Typical Owls)
Species name author Forster, 1772
Population size 50000-99999 mature individuals
Population trend Increasing
Distribution size (breeding/resident) 19,800,000 km2
Country endemic? No
Links to further information
- Additional Information on this species
- 2015 European Red List assessment