Archived 2017 topics: Snowy Owl (Bubo scandiacus): uplist from Least Concern to Vulnerable?

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.

 

References

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.

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6 Responses to Archived 2017 topics: Snowy Owl (Bubo scandiacus): uplist from Least Concern to Vulnerable?

  1. Teemu Lehtiniemi says:

    In Finland number of Snowy Owls seen outside the breeding range (mainly spring and winter) has decreased some 60 % during this century (see https://lintulehti.birdlife.fi:8443/pdf/artikkelit/1923/tiedosto/Linnut_VK2015_030-039_Uhanalaiset_artikkelit_1923.pdf#view=FitH figure 4). Although the yearly sums are pretty low and highly fluctuating (4-227 / year) the trend seems clear and supports the analysis above. Birds seen out of the breeding area are evidently mostly Russian, because there is no correlation between the number of territories in very northern Finland and occurrence outside the breeding range.

    Our breeding population is very marginal on the edge of large breeding range, but breeding is more regular comparing to the end of 20th century. During the 1970’s- 1990’s we had known breeding Snowy Owls only in three years, but during the period 2000-2015, we have had known breeding pairs in seven years (maximum 10 pairs in 3 years). Increase reflects to better monitoring of the core breeding area, but it seems that Snowy Owl is really more regular breeder than it was in the late 20th century.

  2. JF Therrien says:

    With several of my colleagues actually conducting field work in remote places of the Arctic at this very moment (with very limited access to internet), this comment is on behalf of all members of the International Snowy Owl Working Group, which held its 4th gathering a few months ago (Boston, March 2017). The group gathers snowy owl researchers from across the range of the species (breeding and non-breeding) from 9 countries. During the meeting, the group reached the conclusion that the snowy owl status should be re-evaluated, considering the very points mentioned above such as DNA analyses by Marthinsen et al. (2009), as well as population estimates by Potapov and Sale (2013) and Holt et al. (2015).
    We are indeed currently working on a thorough status assessment for the species (including population size, precise and actual distribution range, survival rate, etc), which will most likely provide support for uplisting its status to vulnerable. So we support entirely this proposal.

  3. Denver Holt says:

    I am clearly in favor of re-evaluating the Snowy Owl population estimates worldwide. In fact we have no idea what the historic population was. It may have been small already. In my study area in Barrow, AK, both Snowy Owls and Brown and Collared lemmings are declining significantly over 25 years. Historically however, except for a few studies of brief duration, I do not know with any confidence what the populations were like at Barrow in the past 100 years. Perhaps the owls have just moved to better areas and the population is the same – and perhaps not. Furthermore, it seems to me that all these population estimates – whether true or not – are best guesses. I would like to somehow, and if possible, try to figure out, and simultaneously conduct an international survey to get a better idea of the owls population status on the breeding grounds. This will be no easy task. I mention my concerns in the updated Snowy Owl BNA species account (2015). If we just use existing information, and conduct another population estimate, and extrapolate, we are still guessing. If we ever have to go to court for conservation or management action, it may be difficult to get support based upon guesses. On the other hand, perhaps Christmas Bird Count data, or another survey method – at least in Canada and the U.S. could provide some meaningful results. Can we get the Europeans to conduct a similar count? Anyway, I do not mean to discredit the efforts of others, I just have concerns extrapolating. Lastly, I have been researching and surveying owls for 40 years. One thing stands out to me. Each time we initiated surveys for owls – some species believed to be common, others with regional status, such a species of concern, vulnerable, threatened, etc., we found more owls than we thought and located new areas not know before. I hope this helps.

  4. Roar Solheim says:

    The Norwegian Snowy Owl team are very confident that a re-evaluation of the status of the Snowy Owl worldwide is highly over-due. Although it is hardly possible to get a total population count for the whole Arctic within the same breeding season, we do have enough data on migration of the different ”sub”populations and their breeding grounds that we can make some pretty good assumptions on population sizes, at least for the Fennoiscandia-West-Russian part of the Snowy Owl´s breeding range. The breeding owls we have satellite-tagged in Norway move all the way to the Taymyr peninsula, covering half of the Russian Arctic. The number of breeding pairs found in Fennoscandia during the last two lemming peak years (2011 and 2015) have numbered around 50. Considering the efforts put into searching for breeding owls using helicopters, we are fairly confident that the total number of breeding Snowy Owls both these last two seasons has been lower than 100 pairs. The last record year of breeding Snowy owls in Fennoscandia was 1978, when as many as 200 pairs may have bred in Sweden and Norway. Denver Holt´s point that owls may move to other breeding areas may of course be a potential explanation for the decline we have seen in numbers, but we find it far more likely that there has been a marked population decline in our part of the species´ range during the last 40-60 years. The far distances ”our” owls move into Russia also point to a much lower total number of adult birds from Taymyr to Scandinavia. A total population of just a few hundred pairs as a worst scenario is not unlikely.
    For the Fennoscandian-Russian population we do not have the option of winter counts, as the satellite owls winter in the high Arctic. Snowy Owls are reported observed in steppe areas of Russia/Kazakhstan. But no winter censuses have been carried out in these remote areas as to our knowledge. When we have had birds moving south into Sweden and Norway during winter, these have usually been young birds (juveniles or one year old individuals). The last such occurance of several non-breeding Snowy Owls was in year 2000. Our only option for doing Snowy Owl census work is thus searching for breeding pairs during lemming and vole peak years. The next such peak is expected in 2019.

  5. Gilles Gauthier says:

    I have been studying Snowy owls in the Canadian Arctic for the past 20 years with several Canadian colleagues and especially Jean-François Therrien (who made a comment in this orum). I am also a member of International Snowy Owl Working Group. I totally support the initiative of re-evaluating the status of the species as I strongly believe that population estimates used to make the previous assessment are much too high. We have been tracking snowy owls with satellite transmitters in the eastern Canadian Arctic for the last 10 years and we have documented very extensive movements from year to year. Thus, many individuals seen in different areas in differnt years may actually be the same birds. I believe that the more recent population estimates cited above are more realistic, though I recognize that there is still great uncertainties around these numbers. Nonetheless, I agree that the status of vulnerable species for the Snowy owl is totally justified.

  6. Andy Symes (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2017 Red List would be to list:

    Snowy Owl as Vulnerable under criterion A2bd+3bd+4bd.

    There is now a period for further comments until the final deadline of 4 August, after which the recommended categorisations will be put forward to IUCN.
    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2017 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.