Snowy Owl, Bubo scandiacus, is currently listed as Least Concern as it has not been thought to approach the threshold for listing as Vulnerable under any criterion. It has a very large range spanning across predominantly Arctic regions in the Northern Hemisphere.
Its population size was estimated to number approximately 200,000 individuals (Partners in Flight Science Committee 2013) (although there is some uncertainty over whether this refers to all individuals or only mature individuals), but recently, alternative methodologies have been presented at estimating the global population, which give far lower figures. Potapov and Sale (2013) presented a ‘Loose Boid’ method of estimating population size. They concluded that instead of being evenly distributed across the tundra, snowy owls could be found in seven different loose boids or very thinly distributed groups which may move throughout given areas in line with conditions; in particular food availability. The largest of these boids was suggested to be in central northern Canada and could contain 4,000 pairs (Potapov and Sale 2013). In total, they estimated that, on average, each boid may contain 2,000 pairs and so the global population size would be c.14,000 pairs (Potapov and Sale 2013) or 28,000 mature individuals, which fits with a maximal estimate of 14,000 females suggested by DNA analyses by Marthinsen et al. (2009). However, Potapov and Sale did suggest the population size could be as low as 7,000-8,000 pairs (Potapov and Sale 2013). These population estimates are obviously far lower than previously used, but still they are sufficiently large that this species would not approach the threshold for Vulnerable as a result of its population size, and its Extent of Occurrence is very large and hence would not meet approach the threshold for Vulnerable under criterion B.
The Snowy Owl may, however, be being undergoing high rates of population decline. It is affected by human activity directly, with mortality occurring as a result of entanglement in fishing equipment, electrocution, plane strike and vehicle collisions all being reported from Alberta, Canada (Holt et al. 2015). Illegal hunting and harvesting of individuals also occurs, though the harvest by native people is not thought to have a significant effect. Climate change is also likely to be a significant threat to this species, as it impacts upon the start of spring and the snowmelt in the species’s breeding areas, which can affect prey availability (International Snowy Owl Working Group 2010).
High rates of population decline have been reported in at least the American and Canadian part of its range, with Rosenberg et al. (2016) estimating a 64% decline in Snowy Owl populations in U.S.A. and Canada between 1970 and 2014; with an estimated population in these two countries of <30,000 individuals. Extrapolating backwards this would equate to a decline of c.58% over 3 generations (c.36 years) in the population in these countries. The population figures used by Rosenberg et al. (2016) would appear to continue to use the same criteria that were used to estimate a global population of 200,000 individuals in 2013; and so trend data should still hold as methodologies of generating estimates have been kept relatively consistent – as this deals with proportional change.
This trend data can then be used in conjunction with Potapov and Sale’s (2013) ‘Loose Boids’. By sub-dividing the global population into these thinly distributed groups and assuming 4,000 pairs are found in the central northern Canadian Boid, this would then mean that on average c.1,667 pairs are found in each other grouping. One of the other 6 boids proposed by Potapov and Sale (2013) is restricted to North America [on Wrangel Island] and one more may move into North America [ranging from the Indrigirka River in Russia to Victoria Island in Canada]. Therefore, there may be between 5,667 and 7,333 pairs in North America at a given time; equating to 6,667-8,333 pairs outside of this range. Taking a very crude view that declines have only occurred in North America, and extrapolating backwards, the population estimates for this region would equate to global population declines over the past 3 generations in the range of 35.7-41.8%. This is not the case though, as the Snowy Owl is known to have declined in the Western Palearctic (e.g. Portenko 1972; Solheim 1994, 2004; I. J. Øien in litt. 2014), and climate change will be likely having global impacts on this species rather than local impacts. Therefore the global decline over 3 generations may in fact be more similar to that for North America alone – 58%. It should be noted that Snowy Owl populations do fluctuate (BirdLife International 2015) and so this may affect population trend estimates, but given the estimates presented, and the potential for threats to continue into the future then this species likely warrants listing at least as Vulnerable under criteria A2bd+3bd+4bd (past, future and ongoing decline of 30-49% over three generations where the causes of the reduction have not ceased OR aren’t understood OR may not be reversible); though we request any further evidence of declines in Eurasia to see whether it might qualify as Endangered (decline of 50-79% over three generations).
We welcome any further comments on this proposed uplisting.
BirdLife International. 2015. European Red List of Birds. Office for Official Publications of the European Communities, Luxembourg.
Holt, W.; Berkley, R.; Deppe, C.; Enríquez Rocha, P.; Petersen, J. L.; Rangel Salazar, J. L.; Segars, K. P.; Wood, K. L.; Garcia, E. F. J. 2015. Snowy Owl (Bubo scandiacus). 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.
International Snowy Owl Working Group. 2010. International Snowy Owl Working Group, Resolution Document, Second meeting, Saskatoon February 2010.
Marthinsen, G.; Wennerberg, L.; Solheim, R.; Lifjeld, J. T. 2009. No phylogeographic structure in the circumpolar snowy owl (Bubo scandiacus). Conserv. Genet. 10: 923-933.
Partners in Flight Science Committee. 2013. Population Estimates Database, version 2013. Available at: http://rmbo.org/pifpopestimates. (Accessed: 09/07/2015).
Portenko, L. A. 1972. Die Schnee-Eule, Nyctea scandiaca. A. Ziemsen Verlag, Wittenberg Luterstadt
Potapov, E.; Sale, R. 2013. Chapter 8 Numbers and Population Density. Pp 159-198 in
Potapov, E.; Sale, R. (eds). The Snowy Owl. T & AD Poyser, London.
Rosenberg, K. V.; Kennedy, J. A.; Dettmers, R.; Ford, R. P.; Reynolds, D.; Alexander, J. D.; Beardmore, C. J.; Blancher, P. J.; Bogart, R. E.; Butcher, G. S.; Camfield, A. F.; Couturier, A.; Demarest, D. W.; Easton, W. E.; Giocomo, J. J.; Keller, R. H.; Mini, A. E.; Panjabi, A. O.; Pashley, D. N.; Rich, T. D.; Ruth, J. M.; Stabins, H.; Stanton, J.; Will., T. 2016. Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.
Solheim, R. 1994. Snøugle Nyctea scandiaca. P. 272 in: Gjershaug, J. O.; Thingstad, P. G.; Eldøy, S.; Byrkjeland, S. (eds) Norsk fugleatlas. NOF, Klæbu.
Solheim, R. 2004. 30 år uten snøugle. Vår fuglefauna 27: 102–108.