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Bubo scandiacus 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Strigiformes Strigidae

Scientific Name: Bubo scandiacus (Linnaeus, 1758)
Regional Assessments:
Common Name(s):
English Snowy Owl
Synonym(s):
Bubo scandiaca
Taxonomic Source(s): Cramp, S. and Simmons, K.E.L. (eds). 1977-1994. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic. Oxford University Press, Oxford.
Taxonomic Notes: Bubo scandiacus (del Hoyo and Collar 2014) was previously listed as B. scandiaca.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2bd+3bd+4bd ver 3.1
Year Published: 2017
Date Assessed: 2017-10-01
Assessor(s): BirdLife International
Reviewer(s): Symes, A.
Contributor(s): Lehtiniemi, T., Therrien, J., Holt, D., Solheim, R., Gauthier, G. & O'Brien, T.
Facilitator/Compiler(s): Ekstrom, J., Butchart, S., Ashpole, J, Symes, A., Westrip, J.
Justification:
This iconic large owl of Arctic regions has been uplisted to Vulnerable as it is undergoing rapid population declines in North America and probably also in northern Europe and Russia. Drivers of the decline are uncertain but likely include climate change effecting prey availability, as well as collisions with vehicles and infrastructure. There remains some uncertainty about the overall rate of decline, and if it proves to be even higher the species may be eligible for further uplisting to Endangered.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species has a huge range across predominantly Arctic regions from western Scandinavia through northern Russia to Alaska (USA), northern Canada and Greenland (Denmark), and has also bred occasionally in Iceland and the UK. In winter birds move further south into the USA, northern Europe and north Asia.
The global population size was previously estimated to number approximately 200,000 individuals (Partners in Flight Science Committee 2013), however recent estimates are much lower, and it is now thought that the total population may number some c.14,000 pairs or even as low as 7,000-8,000 pairs (Potapov and Sale 2013).
Countries occurrence:
Native:
Canada; China; Faroe Islands; Finland; Greenland; Iceland; Japan; Kazakhstan; Latvia; Norway; Russian Federation (Central Asian Russia, Eastern Asian Russia, European Russia); Saint Pierre and Miquelon; Svalbard and Jan Mayen; Sweden; United Kingdom; United States
Vagrant:
Albania; Austria; Belarus; Belgium; Bermuda; Croatia; Czech Republic; Denmark; France; Germany; Hungary; Iran, Islamic Republic of; Ireland; Korea, Democratic People's Republic of; Korea, Republic of; Kyrgyzstan; Luxembourg; Mongolia; Montenegro; Netherlands; Pakistan; Poland; Portugal; Serbia; Slovakia; Turkmenistan; Ukraine
Additional data:
Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:38100000
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:No
Upper elevation limit (metres):300
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The 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 individuals or mature individuals), but recently, alternative methodologies have been presented 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. 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 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, they also suggested that the population size could be as low as 7,000-8,000 pairs (Potapov and Sale 2013).

The European population is estimated at 700-2,300 pairs, which equates to 1,400-4,600 mature individuals (BirdLife International 2015).





Trend Justification:  

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 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. 

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; T. Lehtiniemi in litt. 2017), and climate change will be likely having global impacts on this species rather than local impacts. Therefore the global decline over three 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 is likely to be undergoing global declines of 30-49% in three generations, or possibly even higher. 

Current Population Trend:Decreasing
Additional data:
Number of mature individuals:28000Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:No
Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:

Breeds on open tundra from near tree-line to edge of polar seas, with hummocks or rocks and sparse low vegetation and dwarf shrubs and lichen; locally also coastal fields and open moorland, usually at elevations below 300 m, except in Norway (where lemmings occur only on mountains at 1,000 m or higher). In winter, also marshes, fields and dunes (Holt et al. 2017).

Lemmings (LemmusDicrostonyx) and other voles (MicrotusClethrionomys) are major food items, at times probably exploited exclusively; other prey is taken according to availability, include other mammals to size of hares, birds to size of ptarmigans (Lagopus), ducks and medium-sized geese, occasionally fish, amphibians, crustaceans and beetles (Holt et al. 2017).

It is generally monogamous and often pairs for life; but with occasional polygyny and polyandry. The nest is a shallow scrape on ground, usually in a slightly elevated site  (Holt et al. 2017).

It is most active at dusk and dawn, but forages throughout the day in summer. It is mostly migratory and nomadic, with some remaining in the breeding area all year if conditions allow. Movements are unpredictable and related to abundance of prey species; thought to vary considerably from region to region across polar tundra, and intensity of movements fluctuates annually (Holt et al. 2017).

Systems:Terrestrial; Freshwater
Continuing decline in area, extent and/or quality of habitat:Unknown
Generation Length (years):12.1
Movement patterns:Full Migrant

Threats [top]

Major Threat(s): Harvesting of the species for food, feathers and claws by native peoples may have local impact on population, but unlikely to have any wider effect on total numbers. Many apparently die from starvation during irruptive southerly movements from arctic regions. Electrocution, aeroplane strikes, collision with vehicles and entanglement in fishing equipment have all been identified as sources of mortality in Alberta, Canada (Holt et al. 2017). Climate change has a significant impact on the onset of spring and snowmelt in the breeding areas which may change the availability of prey for the species (International Snowy Owl Working Group 2010).

Conservation Actions [top]

Conservation Actions: Conservation and research actions underway
An International Snowy Owl Working Group gathers Snowy Owl researchers from across the range of the species (breeding and non-breeding) from 9 countries. The group is working on a thorough status assessment for the species, including population size, precise distribution range, survival rate etc (J. F. Therrien in litt. 2017). Satellite tracking projects in the Canadian Arctic and Norway have helped document that any individuals make extensive movements, suggesting that the population may previously have been overestimated (R. Solheim and G. Gauthier in litt. 2017)

Conservation and research actions needed
Clarify population size and trend by carrying out coordinated surveys across breeding grounds during lemming peak years and repeating these in subsequent peak years. Work to enact policies designed to protect large birds from electrocution, vehicle and aeroplane strikes.


Citation: BirdLife International. 2017. Bubo scandiacus. The IUCN Red List of Threatened Species 2017: e.T22689055A119342767. . Downloaded on 15 December 2017.
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