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Snowy Owl

Bubo scandiacus

Order:
Strigiformes
Family:
Strigidae
Sections

Distribution, Migration and Habitat

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Figure 1. Breeding and wintering distribution of Snowy Owls in North America.
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eBird range map for Snowy Owl

Generated from eBird observations (Year-Round, 1900-2017)

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Figure 3. Frequency of Snowy Owl occurrence, Christmas Bird Counts 1960-1981.

Frequency = the proportion of counts reporting owls.

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Snowy Owl breeding habitat, Bathurst Island, Nunavut, June.

Snowy Owls favor wide-open expanses of tundra for breeding. During winter they are found in more varied habitats, but perhaps unsurprisingly they still favor open areas frequenting farmlands, beaches, and airports. They generally shun high elevation montane areas., Jun 20, 2008; photographer Gerrit Vyn

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Snowy Owl nest and eggs, Barrow, AK, June.

Snowy Owls nest on the ground in barren arctic tundra. , Jun 05, 2006; photographer Gerrit Vyn

Distribution in the Americas

Breeding Range

Breeding latitude from about 60⁰ to 82⁰ N, most often associated with the distribution of lemmings (Dicrostonyx and Lemmus), although sometimes with that of other species of mammals and seabirds.

In North America in the w. Aleutians (Attu, Buldir), Hall I. (Bering Sea), and from n. Alaska (http://www.fws.gov/alaska/nwr/arctic/birdlist.htm) and throughout the Canadian Arctic Islands north to Ellesmere I., south to coastal w. Alaska (Hooper Bay), n. Yukon (primarily Herschel I.; Sinclair et al. 2003), n. Mackenzie, s. Keewatin, ne. Manitoba (Churchill; http://www.birdatlas.mb.ca/mbdata/maps.jsp?lang=en), n. Quebec and n. Labrador (Todd 1963). See also Figure 1 and AOU 1998 and supplements for specific locations.

Breeding sites are not always occupied annually owing to fluctuating food resources and this owl's nomadic habits. Perhaps the first nest ever recorded in North America, by non-native people, was located in Grinnell Land at 82⁰ 40' N, 20 June 1876 (see Bent 1938).

Winter Range

When food is available the Snowy Owl is one of few avian species capable of withstanding Arctic winters – both in terrestrial and marine environments. Indeed, it has been recorded wintering at 82⁰ N (Hart 1880, also in Gessaman 1972, 1978, see also Manning et al. 1956 for Banks I., Canada). Thus able to winter at breeding latitudes but also found south throughout s. Canada and the n. United States; rarely south to latitudes of central California, Colorado, Florida, Georgia, Kentucky, Louisiana, Nevada, Oklahoma, South Carolina, Texas, Utah (Bent 1938, AOU 1998). See Figure 1 and eBird data (Dec-Feb for all years).

Two reportedly shot in Bass Cove, Bermuda in 1843 (Bent 1938, AOU 1998), and one photographed in Bermuda on 28 Nov 2013 (see Bernews 28 Nov 2013, Bermuda and Bermuda Audubon Society).

During winter, often associated with open water, e.g., known to winter on or near pack ice in the Bering Sea (Fay and Cade 1959, Irving et al. 1970, McRoy et al. 1971). Recent satellite tracking data indicate the ability to winter on pack-ice, probably near leads, cracks in ice, and polynyas (Fuller at al. 2003, Therrien et al. 2011). Although it is tempting to infer satellite data as new information, Eskimos hunters have known about these behaviors for centuries. Most irruptions occur more regionally as in winter 2013/2014 from Great Lakes to New England.

During the winter irruption of 2011/2012, irruption migration was widespread, with Snowy Owls recorded in large numbers from Atlantic to Pacific coasts, including 35 states within the continental USA and all southern Canadian provinces, with individuals recorded as far south as Arkansas, Oklahoma, Texas, Utah, and S. Carolina (see eBird 2012, Dec- Feb map). One Snowy Owl somehow reached Hawaii (see below).

Distribution Outside the Americas

Breeding Range

From n. Greenland, n. Scandinavia, n. Russia (including Wrangel I., s. Novaya Zemlya, and n. Siberia) south to the limits of tundra in Eurasia and the Commander Is.; rarely to the British Isles and Iceland (Mikkola 1983, Cramp 1985, Potapov and Sale 2012). Has nested on Fetlar I. (60⁰ 39' N; probably the most southerly breeding record) in the Shetland Islands, UK (Tulloch 1968); suspected nesting on other Shetland Islands, at least historically (Saxby 1863, 1874).

Winter Range

Irregular from breeding range south to Iceland, British Isles, n. continental Europe, central Russia, n. China, and Sakhalin (Cramp 1985). Accidental in e. European countries, and in the Azores, the Mediterranean region, Iran, nw. India, and Japan.

In November 2011, one Snowy Owl arrived at the Honolulu International Airport, Hawaii. It seems highly unlikely this individual flew the entire distance without stopping; as the species is known to board ships at sea, it seems logical to conclude it used ships as a stopover during this journey; see numerous stories on the internet – Snowy Owl/ Hawaii). This represents the most southernmost record for the species.

Nature of Migration

Many Snowy Owls appear to be regular migrants, while others spend the winter in or near arctic breeding grounds. However, variation in numbers, age, and sex make each year different and lead to speculation about population demographics and distribution. It was believed that Snowy Owls migrated south from their Arctic breeding grounds when lemming populations declined during the purported 3-4 or 5-6 year lemming (and perhaps hare (Lepus) cycle (Bent 1938, Snyder 1943, Shelford 1943, 1945, Gross 1947, Chitty 1950, Godfrey 1986). Occasionally Snowy Owl “flights” occur in two successive winters, the second involving smaller numbers (Godfrey 1986).

Such speculation was understandable, as breeding Snowy Owls are known to prey almost exclusively on lemmings; e.g., in North America, 24 major invasions were recorded between 1833 and 1945, in various regions with varying amplitude (Gross 1947). These invasions were correlated with high populations of Arctic Fox and other lemming predators, leading to the conclusion that Snowy Owls occurred when lemming populations declined, on average every 3-5 yr. This led in turn to the idea that Snowy Owls invasions could be predicted (Gross 1947).

Indeed, in some years very large numbers of Snowy Owls migrate south of their breeding grounds to s. Canada and the n. U.S. This is often referred to as an incursion, irruption, invasion, great flight, nomadism, vagrant migration, wandering (see Holt and Zetterberg 2008). These migrations consist of mostly young owls in their first year of life, about 5 mo old, but various age classes of adults occur as well (e.g., see Robbins and Otte 2013). The owls usually arrive on wintering grounds from late Oct and Nov, but in some years earlier. There is no quantitative definition of irruptions; amplitude can vary greatly from irruption to irruption.

At times the link between Snowy Owl irruptions and the lemming cycle is convincing, and at other times it is not. Unfortunately, there are no large-scale synchronous data sets on lemming numbers and Snowy Owl breeding productivity in the North American Arctic. Indeed, lemming research on the north slope of Alaska suggests that statewide synchrony in lemmings populations does not exist (Pitelka and Batzli 1993, DWH unpubl. data). Similar data for lemmings reported from other areas of Canada give mixed results (Krebs 1993).

The migration irruption of 2011/2012 was one of the most widespread on a continental basis in recent years and owls were recorded in every Canadian province and in 31 states within the U.S. This was followed by the 2013/2014 irruption that was more regional in nature, occurring from the Great Lakes to the Northeastern U.S., with many isolated reports further to the south including Florida, Louisiana, and Bermuda. N. Smith banded 176 Snowy Owls in Massachusetts during this period, mostly from Logan International Airport, Boston.

Thus reasons for large-scale movements remain unclear. However, food and weather certainly play a role, although there are no supporting data for the prey population decline. One fact is consistent, however: when large-scale movements occur, most individual Snowy Owls are young of the year. This suggests lemmings were abundant during the breeding season prior to the autumn migration, and that Snowy Owls had a productive breeding season (see Holt and Zetterberg 2008). Apparently, cyclic irruptions of Snowy Owls rarely occur in Europe, perhaps owing to the small area of tundra in this area (see Cramp 1985).

Kerlinger et al. (1985) explored Snowy Owl sighting and distribution records from Christmas Bird Counts (CBC), and American Bird / Audubon Field Notes (AFN) in one of the first quantitative attempts to confirm that winter irruptions occurred regularly at 4 yr intervals. They concluded there was no uniform distribution of wintering Snowy Owls for North America and that numbers fluctuated widely from year to year in eastern and western zones, with relatively low numbers of owls in most years but irruptions in some years. On the Great Plains of s. Canada and the n. U.S., the owls were not irruptive, instead being regular annual migrants with numbers ranging from 2-10 times that of other regions. There was no indication of cyclic events, and the region was considered prime Snowy Owl winter habitat.

Although a regular 3-4 yr cyclic interval / irruption was not supported by Kerlinger et al.'s 1985 time series analysis, irruptions did occur “frequently” at intervals of 3 and 4 yr. The authors concluded that irruptions occurred rarely continent-wide and rarely synchronously over wide geographic areas.

In another analysis, Kerlinger and Lein (1986) looked at 834 museum skins from 34 museums distributed throughout Canada and U.S. The authors divided Canada and the U.S. into three longitudinal and four latitudinal zones, to analyze distributional and age and sex of the museum specimens. They separated skins into four sex and age classes 1) adult female; 2) immature female; 3) adult male; 4) immature male, and tested three hypotheses: 1) body size; 2) arrival time; and 3) social dominance, related to winter geographic distribution of birds. Although there was distributional overlap in the four age-sex classes, they concluded immature males wintered furthest south, adults wintered north of immature birds and adult females wintered furthest north. They attributed this distribution to social dominance, with females dominant over males.

Their data also buttressed Kerlinger et al.'s (1985) results that Snowy Owls are regular winter visitors to the Great Plains of the s. Canada and n. U.S. Migrants to the eastern and western portions of s. Canada and the n. U.S. appear to represent irruption migrations.

While these data were convincing, few museum specimens were present from high northern latitudes where both male and female Snowy Owls winter. Thus, there may be some biases, and field observations are needed to corroborate results. Furthermore, if social dominance is a factor, this may not fully explain why males migrate hundreds of miles south of females.

In yet another study, looking at Snowy Owl winter population ecology, Kerlinger and Lein (1988a) once again used CBC data, AFN / American Birds, and road counts from 1961-1985, to decipher long-term patterns of abundance on the northern Great Plains of North America (Alberta, Manitoba, Saskatchewan; Montana, N. and S. Dakota). The authors concluded Snowy Owl abundance did not fluctuate synchronously on the northern Great Plains over a 24 yr period, and that distribution was patchy in space and time, within or between years.

In one review from the Pacific Northwest, Patterson (2007) reported that irruptions occurred at approximately 8-12 yr intervals. However, the continent-wide irruption migration of the winter 2011/2012 was followed by a sequential irruption in the Pacific Northwest during the winter of 2012/2013, buttressing Godfrey's (1986) statement that irruptions can occur in consecutive winters, although amplitude varies.

If lemmings are abundant, some Snowy Owls winter in n. Alaska, sometimes near breeding grounds (Bailey 1948, Pitelka, 1955a,b, DWH); this has been known by Eskimos for centuries. The first satellite tracking data for this species from Barrow, AK, showed that some post-breeding females remained in the Arctic all winter and migrated in an east-west direction from Alaska to Russia (Fuller et al. 2003). These owls appeared to spend time at sea where it was believed they hunted sea ducks and sea birds in areas of open water, such as polynyas or leads. These satellite data confirm winter observations of Snowy Owls from Eskimo hunters, bird and mammal observers on ice-breaking ships, and other winter explorers (Hart 1880, Manning et al. 1956, Fay and Cade 1959, Irving et al. 1970, McRoy et al. 1971, Robertson and Gilchrist 2003).

Although most large-scale migration or irruption migrations are young owls in their first year of life, some adult females and males also move south. One problem, however, is that many after-hatch-year females still look heavily barred and could be incorrectly aged if not in hand to examine molt. Finally, winter numbers of Snowy Owls vary from year to year and are likely tied to prey populations during the previous breeding season. Whether these irruption migrations are really due to lack of food in northern areas, or to a combination of other factors, remains unresolved (Holt and Zetterberg 2008).

Timing and Routes of Migration

In North America, some Snowy Owls migrate southward during Arctic winters while some remain in the Arctic. Not all routes of migration are known, but coastlines, prairies, river valleys, and perhaps mountain ridgelines help guide direction. Of the migratory owls that leave the Arctic, the earliest ones arrive on wintering grounds in s. Canada and the n. U.S. towards the end of Oct, but usually mid-to-late Nov (see Bent 1938, Gross 1947, Parmelee 1992, Smith 1997). During a 2 yr study, Kerlinger and Lein (1988) suggested a “wave” of migrants in Alberta, with the first showing up by late Nov, followed by a second wave in mid-Dec, and a third in early Jan. Adult females were seen before males. During a 15 yr study (1981-1997) at Logan Airport, along the Atlantic coast (East Boston, MA), most Snowy Owls arrived in mid-Nov and left by late-Apr, with the earliest date of arrival 22 Oct and the latest departure 07 Jul (Smith 1997).

Birding records and satellite tracking buttress some of the north-south migration pattern, but satellite tracking often shows erratic movements (Fuller et al. 2003, Therrien et al. 2011; see also satellite tracking studies by N. Smith, R. Solheim, D. Zazelenchuk). Fuller et al. (2003) suggested the non-traditional east-west long distance movements observed among Snowy Owls from Barrow, AK, allowed them to adapt to areas where food resources were patchy – a reasonable explanation.

By Mar or Apr, Snowy Owls begin to move north, back to Arctic tundra. On occasion, a few wintering owls linger on wintering grounds well into spring and summer. Reasons for this are unknown, but records of Snowy Owls exist in May (Massachusetts), Jun (New Hampshire), and Jul (Labrador) (in Bent 1938). During the large-scale irruption migration of winter 2011/2012, Snowy Owls were seen in July in Washington and Oregon. In most cases these owls appeared to be birds in their first year of life (i.e., non-breeders).

Banding Records

Figure 8. Between 1924 and 2014, 5,032 Snowy Owls were banded in North America -- in all Canadian Provinces and 21 states within the U.S. Where known, sex ratio was approximately 36.8% (n = 1,851) female, 30.1% (n = 1,514) male, and 33.1% (n = 1,667) unknown. Of the banded owls, approximately 20% were banded as nestlings, mostly from Barrow, AK.

Encounter rate for these birds was low (8.7% -- 438 of 5,032), with records coming from 9 Canadian Provinces, 1 Canadian Territory, 16 U.S. states, and Russia. Of these 438 encounters, 35.6% (N = 156) occurred outside the banding site. Only 54 (12.3%) of the encounters were recaptures; 331 (75.6%) were found dead, injured, shot or entangled. Visual confirmation by telescoping, color markers, or other means was recorded for 40 (9.1%) of the encountered owls; the remaining 13 were unknown or miscellaneous.

Sex ratio for encountered owls was 46.6% (n = 204) female and 34.7% (n = 152) male, with 18.7% (n = 82) unknown. (N.B., sexing in the field is difficult so these data are to some extent estimates). Encountered owls were originally aged as 205 hatch or second year birds (46.8%) and 163 older (37.2%). Only 24 (5.4%) of the 438 encounters were banded as nestlings.

Where exact banding and encounter dates are known, the mean time interval was 2.01 yr, n = 390, range 23 d to 16 yr). The longest movement came from a nestling banded near Cambridge Bay, Nunavut, Canada and encountered 2 yr later along the Strait of Tartary, Russia, approximately 5,600 km distance. Another banded as a nestling from Barrow, AK, was encountered 4,800 km away at North Bay, Ontario, Canada. Other owls banded at Nunavut have been encountered in: Maine (3,200 km), Ontario (3,000 km), Wisconsin (2,700 km), and Quebec (2,200 km). A nestling banded at Cambridge Bay, Nunavut, Canada was encountered 1,700 km away in N. Dakota.

Areas with high rates of encounter areas, away from the origin of banding: Minnesota (121), Alberta (65), Wisconsin (53), Ontario (41), and Massachusetts (31).

Migratory Behavior

Little known. Individuals are not known to migrate together, but data from satellite-tracked owls showed individuals sometimes moved on similar dates and directions, likely using similar routes during migration (Fuller et al. 2003).

Observations from ships at sea also indicate that small groups may move at the same times and perhaps even together (see below). There are numerous reports of Snowy Owls boarding ships at sea; e.g., two boarded a ship ~ 500 km off the coast of Newfoundland, while another boarded a ship en route from Nova Scotia to Iceland, ~ 800 km from land (Gross 1947). During the irruption migration of winter 2013/2014 from the Great Lakes to the ne. U.S., at least nine Snowy Owls boarded a ship during a storm off the coast of Newfoundland, Canada. Apparently the owls stayed on board until arriving off the coast of Spain, France and eventually the Netherlands. See www.rtlnieuws.nl/nieuws/laatste-videos-nieuws/sneeuwuil-neemt-gewoon-de-boot-naar-nederland, among other Dutch stories.

“About a dozen” Snowy Owls boarded an ice-breaker vessel approximately 100 km out to sea (71°23'N; 133°51'W), from Tuktoyaktuk, in the Mackenzie River Delta, Northwest Territories, Canada, on 29 Sep 2008 (D. Hutchinson, pers. comm.). The owls appeared on the ship rather suddenly and stayed approximately 12 h. Photographs suggested most of the birds were young of the year. In another report, 5 Snowy Owls roosted on a Shell Oil GPS antenna about 30 km off the coast of Alaska (A. M. Macrander, pers. comm).

Control and Physiology of Migration

No information, but see Gessaman (1972, 1978) Siegfried et al. (1975) for related information.

Satellite tracking studies since the late 1990's have buttressed information from observations and banding studies, and provided many new insights into Snowy Owl movements. Some of these data support the traditional north – south migration, while others indicate east-west movements, and even erratic movements. Further, these data hint of long-term memory of travel routes by Snowy Owls. Currently the only published satellite tracking data for Snowy Owls is that of Fuller et al. (2003), and Therrien et al. (2011a), both from breeding grounds.

Since 2000, 22 transmitters have been deployed on wintering Snowy Owls from Logan Airport, Boston, MA (N. Smith, unpubl. data). Fifteen of these owls migrated north beyond Saint Lawrence Straight, Quebec, Canada. Eight of these owls summered from n. Quebec to Baffin Island. Seven of these 8 owls left summering grounds returning south. Five of the owls wintered in se. Canada / ne. U.S. By spring, these five owls returned north and three summered in n. Canada. Apparently the transmitters stopped functioning on all owls by this second summer (N. Smith, unpubl. data).

The movement data indicated these owls often moved quickly, covering hundreds of kilometers in a few days, and then settled in apparent stopover areas (i.e. Saint Lawrence Straight, Quebec) for prolonged periods, eventually moving on again. This behavior was consistent on both north and south migrations. The owls tended to migrate north along western longitudes and south along eastern longitudes (N. Smith, unpubl. data).

In Feb 2012, a transmitter attached to a female at Logan Airport, Boston, MA enabled Smith to track an owl to Nunavut, Canada. The owl migrated north along Hudson Bay's eastern shore during spring migration and returned south along Hudson Bay's western shore during the autumn migration. It eventually returned to Logan Airport the following Nov. Satellite data indicated a 10,500 km (7000 mile) round trip.

Are the movements exhibited by satellite-tracking considered migration or other? Clearly in some cases satellite-tracked owls moved in typical north-south migrations, but others remained in the Arctic and showed more of an east-west movement (Fuller et al. (2003), or apparently erratic movements (Therrien et al. 2011a). Thus, Snowy Owls may use several strategies to cope with winter. Unfortunately, data may be skewed to females because few males have been tracked by satellite.

Habitat

Breeding Range

Arctic tundra habitat throughout its circumpolar range. These include desert Arctic tundra, wet tundra, coastal tundra, and Arctic islands. Less common in low shrub-like inland tundra and slopes nearing tree line. In all Arctic habitats prefers areas with distinct promontories for nest sites, roosting, and hunting posts. Will use any habitat where prey are available, including marshes, rivers, and lakes. In many areas, nests along coastlines or not far away (see Cramp 1985, Parmelee 1992, Holt et al. 1999). See also Breeding: nest site.

Spring And Fall Migration

Appears to prefer open habitats, such as coastlines and prairies. However, some individuals must fly over forests and mountains to reach tundra habitats for spring nesting, and open habitats for wintering. No specific habitat described for migration, but coastlines and prairies are probably important. Know to fly from mainland North America and Europe to distant arctic islands and back.

Winter Range

From snow-covered tundra and open water within the ice pack, south to rangelands, farmlands, coast lines, marshes, islands, large forest clearings, and cities and towns bordered by open habitats (Kerlinger et al. 1985, Parmelee 1992, Fuller et al. 2003, Detienne et al. 2008, Therrien et al. 2011a).

South of tundra, winter habitat resembles open flat areas reminiscent of tundra. On the plains of Alberta, observations of wintering Snowy Owls indicated they spent 44% of time in stubble-fields, 30% in summer-fallow, 14% in hayfield, and the rest in pasture, grassland, and sloughs (Lein and Boxall 1979). In a similar study from the same area, Lein and Weber (1979) recognized five habitat types (residential, summer-fallow, stubble-field, hayfield, pasture and slough). The owls were recorded more often than expected on stubble and hayfields, than the other habitats. Stubble-fields were clearly the most frequently used habitat (Lein and Weber 1979). The authors felt these habitats maintained most of the prey species the owls hunted.

Although technically not a marine bird, the Snowy Owl is known to winter in coastal areas south of its breeding range, and also in areas of open seawater within the Arctic. Eskimo marine mammal hunters have long known that Snowy Owls hunt along leads or other open areas of water during winter and early spring. Observers on ships reported Snowy Owls wintering at sea in the Arctic (Fay and Cade 1959, Irving et al. 1970, McRoy et al. 1971). Sea ducks and alcids are usually present in such open water leads, and are hunted by the owls (McRoy et al. 1971, Gilchrist and Robertson 2000, Robertson and Gilchrist 2003). Satellite tracking data (Fuller at al. 2003, Therrien et al. 2011a) buttress the above observations, showing that Snowy Owls often winter on sea ice near open water, and in darkness.

Fossil History

Owls are well represented in the fossil record of Europe and North America (Brodkorb 1971, Olson 1985). Indeed, remains of Nyctea scandiaca (i.e. Snowy Owl) have been reported from European prehistoric sites in: Austria, Azerbaijan, Czechoslovakia, England, France, Germany, Hungary, Italy, Poland, Sardinia, and Spain (Brodkorb 1971).

In North America, remains from Pleistocene deposits in Alaska include: Cape Prince of Wales, Little Kiska I., St. Lawrence I., and in Illinois, the Emmons, Schild and Kruger sites (Brodkorb 1971). Also from Gatineau, Quebec, Canada (Harrington 2003a,b).

An extinct, somewhat more robust Snowy Owl, with 2% longer and 6% thicker bones than the present-day species, is known only from glacial deposits in s. France; described as Nyctea scandiaca gallica (Mourer-Chauviré 1975, in Voous 1988).

Fossil remains of at least 84 Snowy Owls were found in a cave at Pessac-sur-Dordogne, France. Most bones were claws and toes and indicated their use as ornaments. However using Snowy Owls as a food source is also likely (Mourer-Chauvire 1979, in Voous 1988).

The etching of a pair of Snowy Owls and their chicks by Paleolithic people from the late Pleistocene of Europe was discovered on the rock face of a cave, at Les Trois Frères, Ariège, France (Burton 1973, p. 18). Other Snowy Owl cave paintings were reported from caves in Magdelenian of Le Portel (Breuil and Jeannel 1955 in Andrews 1990), and from Aurignacian of Grotte des Trois Fréres (Breuil 1959 in Andrews 1990). It is not known if the report by Burton (1973) and Breuil (1959, in Andrews 1990) were from the same cave. Nonetheless, this was a geological period when Arctic tundra extended south, likely rendering much of France suitable nesting habitat for the species (Burton 1973).

Also see O. Potapova (in Potapov and Sale 2012) for the paleo-geographic history of Snowy Owls, emphasizing Europe.

Recommended Citation

Holt, Denver W., Matt D. Larson, Norman Smith, Dave L. Evans and David F. Parmalee.(2015).Snowy Owl (Bubo scandiacus), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/snoowl1

DOI: 10.2173/bna.10