The snowy owl (''Bubo scandiacus''), also known as the polar owl, the white owl and the Arctic owl, is a large, white owl of the true owl family. Snowy owls are native to the Arctic regions of both North America and the Palearctic, breeding mostly on the tundra. It has a number of unique adaptations to its habitat and lifestyle, which are quite distinct from other extant owls. One of the largest species of owl, it is the only owl with largely white plumage. Males tend to be a purer white overall while females tend to more have more extensive flecks of dark brown.Holt, D. W., M. D. Larson, N. Smith, D. L. Evans, and D. F. Parmelee (2020). ''Snowy Owl (Bubo scandiacus)'', version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. Juvenile male snowy owls have dark markings that may appear similar to females until maturity, at which point they typically turn whiter. The composition of brown markings about the wing, although not foolproof, is the most reliable technique to age and sex individual snowy owls.Solheim, R. (2012). ''Wing feather moult and age determination of Snowy Owls Bubo scandiacus''. Ornis Norvegica (2012), 35: 48–67
Most owls sleep during the day and hunt at night, but the snowy owl is often active during the day, especially in the summertime. The snowy owl is both a specialized and generalist hunter. Its breeding efforts and entirely global population are closely tied to the availability of tundra-dwelling lemmings but in the non-breeding season and occasionally during breeding the snowy owl can adapt to almost any available prey, most often other small mammals and northerly water birds (as well as, opportunistically, carrion). Snowy owls typically nest on a small rise on the ground of the tundra.Hume, R. (1991). ''Owls of the world''. Running Press, Philadelphia. The snowy owl lays a very large clutch of eggs, often from about 5 to 11, with the laying and hatching of eggs considerably staggered. Despite the short Arctic summer, the development of the young takes a relatively long time and independence is sought in autumn.
The snowy owl is a nomadic bird, rarely breeding at the same locations or with the same mates on an annual basis and often not breeding at all if prey is unavailable. A largely migratory bird, snowy owls can wander almost anywhere close to the Arctic, sometimes unpredictably irrupting to the south in large numbers.Sindelar Jr., C. (1966). ''A comparison of five consecutive Snowy Owl invasions in Wisconsin''. Passenger Pigeon, 28(10), 108. Given the difficulty of surveying such an unpredictable bird, there was little in depth knowledge historically about the snowy owl's status. However, recent data suggests the species is declining precipitously.Bent, A. C. (1938). ''Life Histories of North American Birds of Prey (part 2), Orders Falconiformes and Stringiformes (Vol. 170)''. US Government Printing Office. Whereas the global population was once estimated at over 200,000 individuals, recent data suggests that there are probably fewer than 100,000 individuals globally and that the number of successful breeding pairs is 28,000 or even considerably less.Marthinsen, G., Wennerberg, L., Solheim, R. & Lifjeld, J.T. (2009). ''No phylogeographic structure in the circumpolar snowy owl (Bubo scandiacus)''. Conservation Genetics. 10(4): 923–933. While the causes are not well-understood, numerous, complex environment factors often correlated with global warming are probably at the forefront of the fragility of the snowy owl's existence.
Taxonomy
The snowy owl was one of the many bird species originally described by Carl Linnaeus in his landmark 1758 10th edition of ''Systema Naturae'', where it was given the binomial name ''Strix scandiaca''. The genus name ''Bubo'' is Latin for an horned owl and ''scandiacus'' is New Latin for of Scandinavia. The former genera name ''Nyctea'' is derivation of Greek meaning "night". Linnaeus originally described the different plumages of this owl as separate species, with the male specimens of snowy owls being considered ''Strix scandiaca'' and the likely females considered as ''Strix nyctea''. Until recently, the snowy owl was regarded as the sole member of a distinct genus, as ''Nyctea scandiaca'', but mtDNA cytochrome ''b'' sequence data shows that it is very closely related to the horned owls in the genus ''Bubo'' and the species is now thusly often considered inclusive with that genus.Wink, M. & Heidrich, P. (2000). ''Molecular systematics of owls (Strigiformes) based on DNA-sequences of the mitochondrial cytochrome b gene''. Pp. 819–828 in: Chancellor, R.D. & Meyburg, B.U. eds. (2000). ''Raptors at Risk. Proceedings of the V World Conference on Birds of Prey and Owls''. Midrand, Johannesburg, 4–11 August 1998. WWGBP & Hancock House, Berlin & Blaine, Washington. However, some authorities debate this classification, still preferring ''Nyctea''. Often authorities are motivated to retain the separate genus on the grounds of osteological distinctions.Ford, N. L. (1967). ''A systematic study of the owls based on comparative osteology''. PhD diss, Univ. of Michigan, Ann Arbor.
Genetic testing revealed a reasonably distinct genetic makeup for snowy owls, being about 8% genetically distinct from other ''Bubo'' owls, perhaps giving credence to those who count the species as separate under ''Nyctea''. However, a fairly recent shared origin in evolutionary history has been illustrated through a combination of genetic study and fossil review and there is little, other than osteology of the tarsometatarsus, to outright distinguish the snowy owl from other modern species like the Eurasian eagle-owl (''Bubo bubo''). Genetic testing has indicated that the snowy owl may have diverged from related species at around 4 million years ago. Furthermore, it has determined that the living species genetically most closely related to the snowy owl is the great horned owl (''Bubo virginianus''). On a broader scale, owls in general have, through genetic materials, been determined to be a highly distinct group, with outwardly similar groups such as Caprimulgiformes revealed to not be at all closely related. Within the owl order, typical owls are highly divergent from barn-owls.Wink, M., A.-A. El-Sayed, H. Sauer-Gürth and J. Gonzalez. (2009). ''Molecular phylogeny of owls (Strigiformes) inferred from DNA sequences of the mitochondrial cytochrome b and the nuclear RAG-1 gene''. Ardea 97 (4):581–591. Furthermore, the ''Bubo'' genus likely clustered at some point during the evolutionary process with other largish owls, such as ''Strix'', ''Pulsatrix'' and ''Ciccaba'', based on broad similarities in their voice, reproductive behaviors (i.e. hooting postures) and a similar number and structure of chromosomes and autosomes. A number, but not all, of extant typical owls seem to have evolved from an ancient shared common ancestor with the ''Bubo'' owls.Schmutz, S. M., & Moker, J. S. (1991). ''A cytogenetic comparison of some North American owl species''. Genome, 34(5), 714–717. In addition to the question of relationship of the traditional ''Bubo'' owls to the snowy owls, ongoing ambiguity of the relationship of other similarly large-sized owls has been persistent. These have sometimes either been included in the genus or within separate genera, i.e. the ''Ketupu'' or fish owls and the ''Scotopelia'' or fishing owls. Despite the adaptive distinctions, the grouping of these large owls (i.e. ''Bubo'', snowy, fish and perhaps fishing owls) appears to be borne out via research of karyotypes.''Owls of the World: A Photographic Guide'' by Mikkola, H. Firefly Books (2012),
The fossil history of snowy owls is fairly well documented despite some early confusion on how to distinguish the skeletal structure of the snowy owls from eagle-owls.Brodkorb, P. (1971). ''Catalogue of fossil birds, Part 4 (Columbiformes through Piciformes)''. Bulletin of the Florida State Museum, Biological Sciences 15 (4). It was determined that the snowy owl once was distributed much more widely and far farther to the south during the Quaternary glaciation when much of the Northern Hemisphere was in the midst of an ice age. Fossil records shows that snowy owls once could be found in Austria, Azerbaijan, Czechoslovakia, England, France, Germany, Hungary, Italy, Poland, Sardinia and Spain as well as in the Americas in Cape Prince of Wales, Little Kiska Island, St. Lawrence Island, and in Illinois. In the Late Pleistocene the range expanded southward even more so to Bulgaria (80,000–16,000 years, Kozarnika Cave, W Bulgaria). and much of the Italian Peninsula. Pleistocene era fossil from France, i.e. ''B. s. gallica'', showed that the snowy owls of the time were somewhat bulkier (though still notably smaller than contemporary eagle-owls of the times, which were larger than the eagle-owls of today) and ostelogically more sexually dimorphic in size than the modern form (9.9% dimorphism in favor of females in the fossils against 4.8% in the same features today).Mourer-Chauviré, C. (1975). ''Les oiseaux du Pléistocène moyen et supérieur de France''. 2ème fascicule (Vol. 64, No. 2). Persée-Portail des revues scientifiques en SHS. There are no subspecific or other geographical variations reported in the modern snowy owls, with individuals of vastly different origins breeding together readily due to their nomadic habits. Despite apparent variations in body size, environment conditions are the likely variant rather than genetics. No evidence could be found of phylogeographic variation could be found in snowy owls upon testing. Furthermore, the snowy owl appears to have a similar level of genetic diversity as other European owls.
Hybrids
Snowy owls are not known to interbreed with other owl species in the wild, and accordingly, no hybrids of snowy owls and other owl species have yet been sighted in the wild. However, a hobby falconer in Kollnburg, Germany, managed to successfully breed hybrids from a male snowy owl and a female Eurasian eagle-owl (''Bubo bubo'') in 2013. The two resulting male hybrid owls possessed the prominent ear tufts (generally absent in snowy owls), general size, orange eyes, and the same pattern of black markings on their plumage from their Eurasian eagle-owl mother, while retaining the generally black-and-white plumage colours from their snowy owl father. The hybrids were dubbed "''Schnuhus''", a portmanteau of the German words for snowy owl and Eurasian eagle-owl (''Schnee-Eule'' and ''Uhu'', respectively). As of 2014, the hybrids had grown to maturity and were healthy.
Description
The snowy owl, of course, is mostly white. They are purer white than predatory mammals like polar bears (''Ursus maritimus'') and Arctic fox (''Vulpes lagopus''). Often when seen in the field, these owls can resemble a pale rock or a lump of snow on the ground. It usually appears to lack ear tufts but very short (and probably vestigial) tufts can be erected in some situations, perhaps most frequently by the female when she is sitting on the nest. The ear tufts measure about and consist of about 10 small feathers. The snowy owl has bright yellow eyes. The head is relatively small and, even for the relatively simply adapted hearing mechanism of a ''Bubo'' owl, the facial disc is shallow and the ear is uncomplicated. 1 male had ear slits of merely on left and on the right. Females are almost invariably more duskily patterned than like-age males. In mature males, the upper parts are plain white with usually a few dark spots on the miniature ear-tufts, about the head and the tips of some primaries and secondaries whilst the underside is often pure white. Despite their reputation for being purely white, only 3 out of 129 Russian museum specimens of adult males showed an almost complete absence of darker spots. The adult female is usually considerably more spotted and often slightly barred with dark brown on the crown and the underparts. Her flight and tail feathers are faintly barred brown while the underparts are white in base color with brown spotting and barring on the flanks and upper breast. In confusingly plumaged snowy owls, the sex can be determined by the shape of wing markings, which manifest as bars more so in females and spots in males.Lind, H. (1993). ''Different ecology in male and female wintering Snowy Owls Nyctea scandiaca L. in Sweden due to colour and size dimorphism''. Ornis Svecica 3 (3–4):147–158. However, the very darkest males and the lightest females are nearly indistinguishable by plumage. On rare occasion, a female can appear almost pure white, as has been recorded in both the field and in captivity.McMorris, A. (2011). ''Snowy Owls: Age, Sex and Plumage''. Presentation Delaware Valley Ornithological Club. There is some evidence that some of the species grow paler with age after maturity.Dementiev, G. P., Gladkov, N. A., Ptushenko, E. S., Spangenberg, E. P., & Sudilovskaya, A. M. (1966). ''Birds of the Soviet Union, vol. 1''. Israel Program for Scientific Translations, Jerusalem. One study's conclusions were that males were usually but not always lighter and that correctly aging is extremely difficult, sometimes individuals either get lighter, darker or do not change their appearance with age. On the other hand, with close study, it is possible to visually identify even individual snowy owls using the pattern of markings on the wing, which can be somewhat unique in each individual. After a fresh moult, some adult females that previously appeared relatively pale newly evidenced dark, heavy markings. On the contrary, some banded individuals over at least four years were observed to have been almost entirely unchanged in the extent of their markings. In another very pale owl, the barn owl (''Tyto alba''), the sexual dimorphism of spotting appears to be driven by genetics while, in snowy owls, environment may be the dictating factor instead.
The chicks are initially grayish white but quickly transition to dark gray-brown in the mesoptile plumage. This type of plumage camouflages effectively against the variously colored lichens that dot the tundra ground. This is gradually replaced by plumage showing dark barring on white. At the point of fledging, the plumage often becomes irregularly mottled or blotched with dark and is mostly solidly dark gray-brown above with white eyebrows and other areas of the face white. Recently fledged young can already be sexed to a semi-reliable degree by the dark marking patterns about their wings.Seidensticker, M. T., D. W. Holt, J. Detienne, S. Talbot & Gray, K. (2011). ''Sexing young Snowy Owls''. Journal of Raptor Research 45 (4):281–289. The juvenile plumage resembles that of adult females but averages slightly darker on average. By their second moult fewer or more broken bars are usually evidenced on the wing. The extent of white and composition of wing patterns become more dimorphic by sex with each juvenile moult, culminating in the 4th or 5th pre-basic moult, wherein the owls are hard to distinguish from mature adults. Moults usually occur from July and September, non-breeding birds moulting later and more extensively, and are never extensive enough to render the owls flightless. Evidence indicates that snowy owls may attain adult plumage at 3 to 4 years of age, but fragmentary information suggests that some males are not fully mature and/or as fully white in plumage that they can attain until the 9th or 10th year.Ridgway, R., & Friedmann, H. (1914). ''The Birds of North and Middle America: A Descriptive Catalog of the Higher Groups, Genera, Species, and Subspecies of Birds Known to Occur in North America, from the Arctic Lands to the Isthmus of Panama, the West Indies and Other Islands of the Caribbean Sea, and the Galapagos Archipelago'' (Vol. 50). US Government Printing Office. Generally speaking, moults of snowy owls occur more quickly than do those of Eurasian eagle-owls.
The toes of the snowy owl are extremely thickly feathered white, while the claws are black. The toe feathers are the longest known of any owl, averaging at , against the great horned owl which has the 2nd longest toe feathers at a mean of Occasionally, snowy owls may show a faint blackish edge to the eyes and have a dark gray cere, though this is often not visible from the feather coverage, and a black bill. Unlike many other whitish birds, the snowy owl does not possess black wingtips, which is theorized to minimize wear-and-tear on the wing feathers in the other whitish bird types. The conspicuously notched primaries of the snowy owl appear to give an advantage over similar owls in long-distance flight and more extensive flapping flight. The snowy owl does have some of the noise-canceling serrations and comb-like wing feathers that render the flight of most owls functionally silent, but they have fewer than most related ''Bubo'' owls. Therefore, in combination with its less soft feathers, the flight of a snowy owl can be somewhat audible at close range. The flight of snowy owls tends to be steady and direct and is reminiscent to some of the flight of a large, slow-flying falcon. Though capable of occasional gliding flight, there is no evidence that snowy owls will soar. It is said that the species seldom exceeds a flying height of around even during passage. While the feet are sometimes described as "enormous", the tarsus is in osteological terms relatively short at 68% the length of those of a Eurasian eagle-owl but the claws are nearly as large, at 89% of the size of those of the eagle-owl. Despite its relatively short length, the tarsus is of similar circumference as in other ''Bubo'' owls. Also compared to an eagle-owl, the snowy owl has a relatively short decurved rostrum, a proportionately greater length to the interorbital roof and a much longer sclerotic ring surrounding the eyes while the anterior opening are the greatest known in any owl. Owls have extremely large eyes which are nearly the same size in large species such as the snowy owl as those of humans. The snowy owl's eye, at about in diameter, is slightly smaller than those of great horned and Eurasian eagle-owls but is slightly larger than those of some other large owls. Snowy owls must be able to see from great distances and in highly variable conditions but probably possess less acute night vision than many other owls. Based on the study of dioptres in different owl species, the snowy owl was determined to have eyesight better suited to long-range perception than to close discrimination, while some related species such as great horned owls could probably more successful perceive closer objects. Despite their visual limits, snowy owls may have up to 1.5 times more visual acuity than humans. Like other owls, snowy owls can probably perceive all colors but cannot perceive ultraviolet visual pigments. Owls have the largest brains of any bird (increasing in sync with the size of the owl species), with the size of the brain and eye related less to intelligence than perhaps to increased nocturnality and predatory behavior.
Size
The snowy owl is a very large owl. They are the largest avian predator of the High Arctic and one of the largest owls in the world. Snowy owls are about the sixth or seventh heaviest living owl on average, around the fifth longest and perhaps the third longest winged.Weidensaul, S. (2015). ''Owls of North America and the Caribbean''. Houghton Mifflin Harcourt. This species is the heaviest and longest winged owl (as well as the second longest) in North America, the second heaviest and longest winged owl in Europe (and third longest) but is outsized in bulk by about 3 to 4 other species in Asia. Despite being sometimes described as of similar size, the snowy owl is somewhat larger in all aspects of average size than the great horned owl while the similarly specialized taiga-dwelling great grey owl (''Strix nebulosa''), is longer in total length and of similar dimensions in standard measurements, but is shorter winged and much less heavy than the snowy owl. In Eurasia, the Eurasian eagle-owl is larger in all standards of measurements than the snowy owl not to mention two additional species each from Africa and Asia that are slightly to considerably heavier on average than the snowy owl.Mikkola, H. (1983). ''Owls of Europe''. T. & AD Poyser. Like most birds of prey, the snowy owl shows reverse sexual dimorphism relative to most non-raptorial birds in that females are larger than males. Sexual dimorphism that favors the female may have some correlation with being able to more effectively withstand food shortages such as during brooding as well as the rigors associated with incubating and brooding. Females are sometimes described as “giant” whereas males appear relatively “neat and compact”. However, the sexual dimorphism is relatively less pronounced compared to some other ''Bubo'' species.
Male snowy owls have been known to measure from in total length, with an average from four large samples of and a maximum length, perhaps in need of verification, of reportedly .Eckert, A. W. (1987). ''The Owls of North America, North of Mexico: All the Species and Subspecies Illustrated in Color and Fully Described''. Gramercy.Parmelee, D. F. (1972). ''Canada's incredible arctic owls''. Beaver no. summer:30–41.Priklonskiy, S.G. (1993). ''Snowy Owl — Nyctea scandiaca (Linnaeus, 1758)''. In: ''Birds of Russia and adjoining regions: Pterocliformes, Columbiformes, Cuculiformes, Strigiformes''. Moscow, p. 258–270. (in Russian).Keith, L.B. (1960). ''Observations of Snowy Owls at Delta, Manitoba''. Can. Field-Nat. 74:106–112. In wingspan, males may range from , with a mean of . In females, total length has been known to range from , with a mean of and an unverified maximum length of perhaps (if so they would have the second longest maximum length of any living owl, after only the great grey owl). Female wingspans have reportedly measured from , with a mean of . Despite one study claiming that snowy owl had the highest wing loading (i.e. grams per square cm of wing area) of any of 15 well-known owl species, more extensive sampling demonstratively illustrated that the wing loading of snowy owls is notably lower than Eurasian eagle- and great horned owls. The conspicuously long-winged profile of a flying snowy owl compared to these related species may cause some to compare their flight profile to a bulkier version of an enormous ''Buteo'' or a large falcon. Body mass in males can average from , with a median of and a full weight range of from six sources.Earhart, C. M., & Johnson, N. K. (1970). ''Size dimorphism and food habits of North American owls''. The Condor, 72(3), 251–264.Kerlinger, P., & Lein, M. R. (1988). ''Causes of Mortality, Fat Condition, and Weights of Wintering Snowy Owls''. Journal of Field Ornithology, 7–12. Body mass in females can average from , with a median of and a full weight range of . Larger than the aforementioned body mass studies, a massive pooled dataset at six wintering sites in North America showed that 995 males averaged at while 1,189 females were found to average .Chang, A. M., & Wiebe, K. L. (2016). ''Body condition in Snowy Owls wintering on the prairies is greater in females and older individuals and may contribute to sex-biased mortality''. The Auk: Ornithological Advances, 133(4), 738–746. Reported weights of down to for males and of for females are probably in reference to owls in a state of starvation.Pitelka, F. A., P. Q. Tomich & Treichel, G. W. (1955). ''Breeding behavior of jaegers and owls near Barrow, Alaska''. Condor 57:3–18. Such emaciated individuals are known to highly impaired and starvation deaths are probably not infrequent in winters with poor food accesses.Ryabitsev, V.K. (2011). ''Birds of the Urals, Ural Region, and Western Siberia: Guide and Identification Key'' (Ural’sk. Univ., Yekterinburg).Golovatin, M.G. & Paskhalniy, S.P. (2005). ''Ptitsy Polyarnogo Urala (Birds of the Polar Urals)'', Ekaterinburg, Siberia.
Standard measurements have been even more widely reported than length and wingspan. The wing chord of males can vary from , averaging from with a median of .Josephson, B. (1980). ''Aging and sexing snowy owls''. Journal of Field Ornithology . 51: 149- 160.Portenko, L. A. (1972). ''Die Schnee-Eule: Nyctea scandiaca'' (Vol. 454). A. Ziemsen. The wing chord of females can vary from , averaging from with a median of . The tail length of males can vary on average from , with a full range of and a median of . The tail length of females can average from , with a full range of and a median of . Data indicates that slightly longer wing chord and tail lengths were reported on average in Russian data than in American research, however the weights were not significantly different in the two regions. Less widely taken measurements include the culmen, which can measure from with a median average of in males and in females, and the total bill length which is from , with an average in both sexes of . Tarsal length in males averages about , with a range of , and averages about , with a range of , in females.
Identification
The snowy owl is certainly one of the most unmistakable owls (or perhaps even animals) in the world. No other species attains the signature white stippled sparsely with black-brown color of these birds, a coloring which renders their bright yellow eyes all the more detectable, nor possesses their obvious extremely long feathering. The only other owl to breed in the High Arctic is the short-eared owl (''Asio flammeus''). Both species inhabit open country, overlap in range and are often seen by day, but the short-eared is much smaller and more tan or straw-colored in coloration, with streaked brown on chest. Even the palest short-eared owls conspicuously differ and are darker than the snowy owl; additionally the short-eared most often hunts in extended flights.Pyle, P. (1997). ''Identification Guide to North American Birds, Part I: Columbidae to Ploceidae''. Slate Creek Press, Bolinas, CA, USA. More similar owls such as the Eurasian eagle-owl and the great horned owl attain a fairly pale, sometimes white-washed look in their northernmost races. These species do not normally breed nearly as far north as snowy owls but overlaps certainly do occur when snowy owls when the latter owl sometimes comes south in winter. However, even the most pale great horned and Eurasian eagle-owls are still considerably more heavily marked with darker base colors than snowy owls (the whitest eagle-owls are paler than the whitest great horned owls), possess much larger and more conspicuous ear tufts and lack the bicolored appearance of the darkest snowy owls. While the great horned owl has yellow eyes like the snowy owl, the Eurasian eagle-owl tends to have bright orange eyes. The open terrain habitats normally used by wintering snowy owls are also distinct from the typical edge and rocky habitats usually favored by the great horned and Eurasian eagle-owls, respectively.
Vocalizations
The snowy owl differ in their calls from other ''Bubo'' owls, with a much more barking quality to their version of a hooting song. Perhaps as many as 15 different calls by mature snowy owls have been documented.Evans, D. L. (1980). ''Vocalizations and territorial behavior of wintering Snowy Owls''. Am. Birds 34: 748–749.Sutton, G. M. (1932). ''The exploration of Southampton Island. Part II, Zoölogy. Section 2.-The birds of Southampton Island''. Memoirs of the Carnegie Museum 12 (2):1–275. The main vocalization is a monotonous sequence that normally contains 2–6 (but occasionally more), rough notes similar to the rhythm of a barking dog: ''krooh krooh krooh krooh''... The call may end with an emphatic ''aaoow'', which is somewhat reminiscent of the deep alarm call of a great black-backed gull (''Larus marinus''). They will call mainly from a perch but also sometimes do so in flight. The ''krooh'' call of the male snowy owl may perform multiple functions such as competitive exclusion of other males and advertising to females.Taylor, P.S. (1973). ''Breeding behaviour of the Snowy Owl''. Living Bird. 12: 137–154. The calls of this species may carry exceptionally far in the thin air of Arctic, certainly over more than , and maybe even to as much away. The female has a similar call to male but can be higher-pitched and/or more guttural as well as single notes which are often disyllabic, ''khuso''. Female snowy owls have also been known to utter chirps and high screaming notes, similar to those of the nestlings. Both sexes may at times give a series of clucking, squeals, grunts, hisses and cackles, perhaps such as in circumstances when they are excited. The alarm call is a loud, grating, hoarse ''keeea''. Another raspier bark is recorded, sometimes called a "watchman's rattle" call, and may be transcribed as ''rick, rick, rick'', ''ha, how, quack, quock'' or ''kre, kre, kre, kre, kre''. A female attacking to protect her nest was recorded to let out a crowed ''ca-ca-oh'' call, whilst other owls attacking to protect the nest did a loud version of the typical call while circling before dropping down.Sutton, G. M. & Parmelee, D. F. (1956). ''Breeding of the Snowy Owl in southeastern Baffin Island''. Condor 58:273–282. They may also clap their beak in response to threats or annoyances. While called clapping, it is believed this sound may actually be a clicking of the tongue, not the beak. Though largely only vocal in the breeding season, leading to some erroneous older accounts describing the snowy owl as completely silent, some vocalizations have been recorded in winter in the northern United States. Initially, the young of the snowy owl have a high pitched and soft begging call which develops into a strong, wheezy scream at around 2 weeks. At the point when the young owls leave the nest around 3 weeks, the shrill squeals they emit may allow the mothers to locate them.Parmelee, D. (1992). ''Snowy Owl (Nyctea scandiaca)''. No. 10 in: Poole et al. (1992–1993).
Distribution and habitat
Breeding range
The snowy owl is typically found in the northern circumpolar region, where it makes its summer home north of latitude 60° north though sometimes down to 55 degrees north. However, it is a particularly nomadic bird, and because population fluctuations in its prey species can force it to relocate, it has been known to breed at more southerly latitudes. Although the total breeding range includes a little over , only about have a high probability of breeding, i.e. breeding at no more than 3–9-year intervals. Snowy owls nest in the Arctic tundra of the northernmost stretches of Alaska, Northern Canada, and Eurosiberia. Between 1967 and 1975, snowy owls bred on the remote island of Fetlar in the Shetland Isles north of mainland Scotland, discovered by the Shetland RSPB warden, Bobby Tulloch. Females summered as recently as 1993, but their status in the British Isles is now that of a rare winter visitor to Shetland, the Outer Hebrides and the Cairngorms. Older records show that the snowy owls may have once semi-regularly bred elsewhere in the Shetlands. They range in northern Greenland (mostly Peary Land) and, rarely in "isolated parts of the highlands", Iceland.Manniche, A. L. V. (1910). ''The terrestrial mammals and birds of east Greenland; biological observations''. Medd. Grønland 45:1–200. Thence, they are found breeding at times across northern Eurasia such as in Spitsbergen and western and northern Scandinavia. In Norway, they normally breed in Troms og Finnmark and seldom down as far south as Hardangervidda and in Sweden perhaps down to the Scandinavian Mountains while breeding is very inconsistent in Finland.Barth, E. (1949). ''Norwegian Animal Life. Volume 2. Birds''.Jacobsen, K. O. (2005). ''Snøugle (Bubo Scandiacus) Norge. Hekkeforekomster i perioden 1968–2005''. Hekkeforekomster i perioden, 2005. They also range in much of northern Russia, including northern Siberia, Anadyr, Koryakland, Taymyr Peninsula, Yugorsky Peninsula, Sakha (especially the Chukochya River) and Sakhalin. Breeding have also been reported sporadically to the south in the Komi Republic and even the Kama River in southern Perm Krai. Although considered part of the regular range, the last breeding by snowy owls in the Kola Peninsula was not since the early 1980s; similarly, breeding maps show the species in Arkhangelsk Oblast and the Pay-Khoy Ridge but no breeding records known in at least 30 years in either. They range throughout most of the Arctic isles of Russia such as Novaya Zemlya, Severnaya Zemlya, New Siberian Islands, Wrangel Island, Commander and Hall Islands. In North America, the breeding range has been known in modern times to include the Aleutians (i.e. Buldir and Attu) and much of northern Alaska, most frequently from the Arctic National Wildlife Refuge to Utqiaġvik, and more sporadically down along the coastal-western parts such as through Nome, Hooper Bay, the Yukon Delta National Wildlife Refuge, and rarely even south to the Shumagin Islands. The snowy owl may breed extensively in northern Canada, largely making its home in the Arctic Archipelago. Their Canadian breeding range can include broadly Ellesmere Island up to Cape Sheridan, north coastal Labrador, the northern Hudson Bay, perhaps all of Nunavut (especially the Kivalliq Region), northeastern Manitoba, both most of northern mainland and insular Northwest Territories (including the delta of the Mackenzie River) and northern Yukon Territory (where breeding is mostly confined to Herschel Island).Parmelee, D. F., & MacDonald, S. D. (1960). ''The birds of west-central Ellesmere Island and adjacent areas (No. 63)''. Department of Northern Affairs and National Resources. Since breeding and distribution is very small, local and inconsistent in northern Europe, northern Canada and northern Alaska represent the core part of the breeding range for snowy owls along with several parts of northern and northeastern/coastal Russia.
Regular wintering range
During the wintering, many snowy owls leave the dark Arctic to migrate to regions further south. Southern limits of the regular winter range are difficult to delineate given the inconsistency of appearances south of the Arctic. Furthermore, not infrequently, many snowy owls will overwinter somewhere in the Arctic through the winter, though seldom appear to do so in the same sites where they have bred. Due in no small part to the difficulty and hazardousness of observation for biologists during these harsh times, there is very limited data on overwintering snowy owls in the tundra, including how many occur, where they winter and what their ecology is at this season. The regular wintering range has at times been thought to include Iceland, Ireland and Scotland and across northern Eurasia such as southern Scandinavia, the Baltics, central Russia, southwestern Siberia, Sakhalin southern Kamchatka and, rarely, north China and sometimes the Altai Republic. In North America, they occasionally regularly winter in the Aleutian island chain and do so broadly and with a fair amount of consistency in much of southern Canada, from British Columbia to Labrador.Godfrey, W. E. (1986). ''The Birds of Canada''. Revised Edition. National Museums of Canada, Ottawa, ON, Canada. Recent research has indicated that snowy owls regularly winter in several of the northern seas during wintertime, following the leads of sea ice as perching sites and presumably hunting mostly seabirds in polynyas.Therrien, J. F., Gauthier, G., & Bêty, J. (2011). ''An avian terrestrial predator of the Arctic relies on the marine ecosystem during winter''. Journal of Avian Biology, 42(4), 363–369. In February 1886, a snowy owl landed on the rigging of the Nova Scotia steamship ''Ulunda'' on the edge of the Grand Banks of Newfoundland, over from the nearest land. It was captured and later preserved at the Nova Scotia Museum.Gross, A. O. (1947). ''Cyclic invasions of the snowy owl and the migration of 1945–1946''. The Auk, 64(4), 584–601. Surprisingly, some studies have determined that after a high lemming year in North America, a higher percentage of snowy owls were using marine environments rather than inland ones.
Irruptive range
Large winter irruptions at temperate latitudes are thought to be due to good breeding conditions resulting in more juvenile migrants. These result in irruptions occurring further south than the typical snowy owl range in some years. They have been reported, as well as in all northerly states in the contiguous states, as far south as the Georgia, Kentucky, South Carolina, nearly all the Gulf Coast of the United States, Colorado, Nevada, Texas, Utah, California and even Hawaii.American Ornithologists' Union (1957). ''Check-list of North American Birds, 5th edition''. American Ornithologists' Union, Washington, DC, USA. In January 2009, a snowy owl appeared in Spring Hill, Tennessee, the first reported sighting in the state since 1987. Also notable is the mass southern migration in the winter of 2011/2012, when thousands of snowy owls were spotted in various locations across the United States. This was then followed by an even larger mass southern migration in 2013/2014 with the first snowy owls seen in Florida for decades. The nature of irruptions is less well-documented in Eurasia, in part due to the paucity of this owl in the European side, but accidental occurrence, presumably during irruptions, has been described in the Mediterranean area, France, Crimea, the Caspian part of Iran, Kazakhstan, northern Pakistan, northwestern India, Korea and Japan. Stragglers may too turn up as far south as the Azores and Bermuda.
Habitat
Snowy owls are one of the best known inhabitants of the open Arctic tundra. Frequently, the earth in snowy owl breeding grounds is covered with mosses, lichens and some rocks. Often the species preferentially occurs in areas with some rising elevation such as hummocks, knolls, ridges, bluffs and rocky outcrops. Some of these rises in the tundra are created by glacial deposits. The ground is usually rather dry in tundra but in some areas of the southern tundra can also be quite marshy. Not infrequently, they will also use areas of varied coastal habitat, often tidal flats, as a breeding site.Murie, O. J. (1929). ''Nesting of the snowy owl''. The Condor, 31(1), 3–12. Breeding sites are usually at low elevations, usually less than above sea level, but when breeding to the south in inland mountains, such as in Norway, they may nest at as high as . Outside the breeding season, snowy owls may habituate nearly any open landscape. Typically wintering sites are rather windswept with meager cover. These open areas can include those such as coastal dunes, other coastal spots, lakeshores, islands, moorlands, steppes, meadows, prairies, other extensive grasslands and rather shrubby areas of the Subarctic. These may be favored due to their vague similarity to the flat openness of the tundra.Fuller, M., Holt, D. & Schueck, L. (2003). ''Snowy Owl movements: Variation on the migration theme''. Edited by P. Berthold, E. Gwinner and E. Sonnenschein, Avian migration. Berlin: Springer-Verlag. Manmade open sites are now perhaps even more used than natural ones, often agricultural fields and rangeland, as well as large areas of cleared forests.Kerlinger, P., Lein, M.R. & Sevick, B.J. (1985). ''Distribution and population fluctuations of wintering Snowy Owls (Nyctea scandiaca) in North America''. Canadian Journal of Zoology. 63(8): 1829–1834.Doyle, F. I., Therrien, J. F., Reid, D. G., Gauthier, G., & Krebs, C. J. (2017). ''Seasonal movements of female Snowy Owls breeding in the western North American Arctic''. Journal of Raptor Research, 51(4), 428–438. During irruption years when they are found in the Northeastern United States, juveniles frequent developed areas including urban areas and golf courses, as well as the expected grasslands and agricultural areas that older birds primarily use. On the plains of Alberta, observed snowy owls spent 30% of their time in stubble-fields, 30% in summer fallow, 14% in Hayfield and the remainder of the time in pasture, natural grasslands and sloughs. The agricultural areas, large untouched by the farmers in winter, may have had more concentrated prey than the others in Alberta.Lein, M.R. & Webber, G.A. (1979). ''Habitat selection by wintering Snowy Owls (Nyctea scandiaca)''. Canadian Field-Naturalist. 93(2): 176–178. Perhaps the most consistently attractive habitat in North America to wintering snowy owls in modern times may be airports, which not only tend to have the flat, grassy characteristics of their preferred habitats but also by winter host a particular diversity of prey, both pests which rely on humans as well as wildlife attracted to the extensively grassy and marshy strips that dot the large airport vicinities. For example, Logan International Airport in Massachusetts has one relatively one of the most reliable annual populations known in the United States in winter.Smith, N. (1997). ''Observations of wintering Snowy Owls (Nyctea scandiaca) at Logan Airport, East Boston, Massachusetts from 1981 to 1997''. In: ''Biology and conservation of owls of the Northern Hemisphere: 2nd International Symposium'', edited by J. R. Duncan, D. H. Johnson and T. H. Nicholls, 591–596. St. Paul: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. All ages spend a fair amount of their time over water in the Bering Sea, the Atlantic Ocean and even the Great Lakes, mostly on ice floes. These marine and ocean-like freshwater areas were observed to account for 22–31% of habitat used in 34 radio-tagged American snowy owls over two irruptive years, with the tagged owls occurring a mean of from the nearest land (while 35–58% used the expected preferred habitats of grassland, pasture and other agriculture).
Behavior
Snowy owls may be active to some extent at both day, from dawn to dusk, and night. Snowy owls have been seen to be active even during the very brief winter daytime in the northern winter. During the Arctic summer, snowy owls may tend to peak in activity during the twilight that is the darkest time available given the lack of full nightfall. Reportedly, the peak time of activity during summer is between 9:00 pm and 3:00 am in Norway.Hagen, Y. (1960). ''The Snowy Owl on Hardangervidda in the Summer of 1959''. Papers of The Norwegian State Game Research. 2, No. 7. The peak time of activity for those owls that once nested on Fetlar was reported between 10:00 and 11:00 pm.Tulloch, R. J. (1968). ''Snowy Owls breeding in Shetland in 1967''. British Birds 61:119–132. According to one authority, the least active times are at noon and midnight. As days become longer near autumn in Utqiaġvik, the snowy owls in the tundra become more active around nightfall and can often be seen resting during the day, especially if it is raining. During winter in Alberta, snowy owls were tracked in the daytime, despite being also active at night (as they were deemed too difficult to track). In the study, they were most active from 8:00–10:00 am and 4:00–6:00 pm and often rested mostly from 10:00 am to 4:00 pm. The owls were perched for 98% of observed daylight and seemed to time their activity to peak times for rodents. The variation of activity is probably in correspondence with their primary prey, the lemmings, and like them, the snowy owl may be considered cathermal. This species can withstand extremely cold temperatures, having been recorded in temperatures as low as minus 62.5 degrees Celsius with no obvious discomfort and also withstood a 5-hour exposure to minus 93 degrees Celsius but may have struggled with oxygen consumption by the end of this period. The snowy owl has perhaps the second lowest thermal conduction to the plumage on average of any bird after only the Adelie penguin (''Pygoscelis adeliae'') and rivals the best insulated mammals, such as Dall sheep (''Ovis dalli'') and Arctic fox, as the best insulated polar creature.Gessaman, J. A. (1972). ''Bioenergetics of the snowy owl (Nyctea scandiaca)''. Arctic and Alpine Research, 4(3), 223–238. Presumably as many as 7 rodents would need to be eaten daily to survive an extremely cold winter's day. Adults and young both have been seen to shelter behind rocks to shield themselves from particularly harsh winds or storms. Snowy owls often spending a majority of time on the ground, perched mostly on a slight rise of elevation. It has been interpreted from the morphology of their skeletal structure (i.e. their short, broad legs) that snowy owls are not well-suited to perching extensively in trees or rocks and prefer a flat surface to sit upon. However, they may perch more so in winter though do so only mainly when hunting, at times on hummocks, Fenceposts, telegraph poles by roads, radio and transmission towers, Haystacks, chimneys and the roofs of houses and large buildings. Rocks may be used as perches at times in all seasons. Though often relatively sluggish owls, like most related species, they are capable of sudden dashing movements in various contexts. Snowy owls can walk and run quite quickly, using outstretched wings for balance if necessary. This owl flies with fairly rowing wingbeats, occasionally interrupted by gliding on stretched wings. The flight is fairly buoyant for a ''Bubo'' owl.
Taxonomy
The snowy owl was one of the many bird species originally described by Carl Linnaeus in his landmark 1758 10th edition of ''Systema Naturae'', where it was given the binomial name ''Strix scandiaca''. The genus name ''Bubo'' is Latin for an horned owl and ''scandiacus'' is New Latin for of Scandinavia. The former genera name ''Nyctea'' is derivation of Greek meaning "night". Linnaeus originally described the different plumages of this owl as separate species, with the male specimens of snowy owls being considered ''Strix scandiaca'' and the likely females considered as ''Strix nyctea''. Until recently, the snowy owl was regarded as the sole member of a distinct genus, as ''Nyctea scandiaca'', but mtDNA cytochrome ''b'' sequence data shows that it is very closely related to the horned owls in the genus ''Bubo'' and the species is now thusly often considered inclusive with that genus.Wink, M. & Heidrich, P. (2000). ''Molecular systematics of owls (Strigiformes) based on DNA-sequences of the mitochondrial cytochrome b gene''. Pp. 819–828 in: Chancellor, R.D. & Meyburg, B.U. eds. (2000). ''Raptors at Risk. Proceedings of the V World Conference on Birds of Prey and Owls''. Midrand, Johannesburg, 4–11 August 1998. WWGBP & Hancock House, Berlin & Blaine, Washington. However, some authorities debate this classification, still preferring ''Nyctea''. Often authorities are motivated to retain the separate genus on the grounds of osteological distinctions.Ford, N. L. (1967). ''A systematic study of the owls based on comparative osteology''. PhD diss, Univ. of Michigan, Ann Arbor.
Genetic testing revealed a reasonably distinct genetic makeup for snowy owls, being about 8% genetically distinct from other ''Bubo'' owls, perhaps giving credence to those who count the species as separate under ''Nyctea''. However, a fairly recent shared origin in evolutionary history has been illustrated through a combination of genetic study and fossil review and there is little, other than osteology of the tarsometatarsus, to outright distinguish the snowy owl from other modern species like the Eurasian eagle-owl (''Bubo bubo''). Genetic testing has indicated that the snowy owl may have diverged from related species at around 4 million years ago. Furthermore, it has determined that the living species genetically most closely related to the snowy owl is the great horned owl (''Bubo virginianus''). On a broader scale, owls in general have, through genetic materials, been determined to be a highly distinct group, with outwardly similar groups such as Caprimulgiformes revealed to not be at all closely related. Within the owl order, typical owls are highly divergent from barn-owls.Wink, M., A.-A. El-Sayed, H. Sauer-Gürth and J. Gonzalez. (2009). ''Molecular phylogeny of owls (Strigiformes) inferred from DNA sequences of the mitochondrial cytochrome b and the nuclear RAG-1 gene''. Ardea 97 (4):581–591. Furthermore, the ''Bubo'' genus likely clustered at some point during the evolutionary process with other largish owls, such as ''Strix'', ''Pulsatrix'' and ''Ciccaba'', based on broad similarities in their voice, reproductive behaviors (i.e. hooting postures) and a similar number and structure of chromosomes and autosomes. A number, but not all, of extant typical owls seem to have evolved from an ancient shared common ancestor with the ''Bubo'' owls.Schmutz, S. M., & Moker, J. S. (1991). ''A cytogenetic comparison of some North American owl species''. Genome, 34(5), 714–717. In addition to the question of relationship of the traditional ''Bubo'' owls to the snowy owls, ongoing ambiguity of the relationship of other similarly large-sized owls has been persistent. These have sometimes either been included in the genus or within separate genera, i.e. the ''Ketupu'' or fish owls and the ''Scotopelia'' or fishing owls. Despite the adaptive distinctions, the grouping of these large owls (i.e. ''Bubo'', snowy, fish and perhaps fishing owls) appears to be borne out via research of karyotypes.''Owls of the World: A Photographic Guide'' by Mikkola, H. Firefly Books (2012),
The fossil history of snowy owls is fairly well documented despite some early confusion on how to distinguish the skeletal structure of the snowy owls from eagle-owls.Brodkorb, P. (1971). ''Catalogue of fossil birds, Part 4 (Columbiformes through Piciformes)''. Bulletin of the Florida State Museum, Biological Sciences 15 (4). It was determined that the snowy owl once was distributed much more widely and far farther to the south during the Quaternary glaciation when much of the Northern Hemisphere was in the midst of an ice age. Fossil records shows that snowy owls once could be found in Austria, Azerbaijan, Czechoslovakia, England, France, Germany, Hungary, Italy, Poland, Sardinia and Spain as well as in the Americas in Cape Prince of Wales, Little Kiska Island, St. Lawrence Island, and in Illinois. In the Late Pleistocene the range expanded southward even more so to Bulgaria (80,000–16,000 years, Kozarnika Cave, W Bulgaria). and much of the Italian Peninsula. Pleistocene era fossil from France, i.e. ''B. s. gallica'', showed that the snowy owls of the time were somewhat bulkier (though still notably smaller than contemporary eagle-owls of the times, which were larger than the eagle-owls of today) and ostelogically more sexually dimorphic in size than the modern form (9.9% dimorphism in favor of females in the fossils against 4.8% in the same features today).Mourer-Chauviré, C. (1975). ''Les oiseaux du Pléistocène moyen et supérieur de France''. 2ème fascicule (Vol. 64, No. 2). Persée-Portail des revues scientifiques en SHS. There are no subspecific or other geographical variations reported in the modern snowy owls, with individuals of vastly different origins breeding together readily due to their nomadic habits. Despite apparent variations in body size, environment conditions are the likely variant rather than genetics. No evidence could be found of phylogeographic variation could be found in snowy owls upon testing. Furthermore, the snowy owl appears to have a similar level of genetic diversity as other European owls.
Hybrids
Snowy owls are not known to interbreed with other owl species in the wild, and accordingly, no hybrids of snowy owls and other owl species have yet been sighted in the wild. However, a hobby falconer in Kollnburg, Germany, managed to successfully breed hybrids from a male snowy owl and a female Eurasian eagle-owl (''Bubo bubo'') in 2013. The two resulting male hybrid owls possessed the prominent ear tufts (generally absent in snowy owls), general size, orange eyes, and the same pattern of black markings on their plumage from their Eurasian eagle-owl mother, while retaining the generally black-and-white plumage colours from their snowy owl father. The hybrids were dubbed "''Schnuhus''", a portmanteau of the German words for snowy owl and Eurasian eagle-owl (''Schnee-Eule'' and ''Uhu'', respectively). As of 2014, the hybrids had grown to maturity and were healthy.
Description
The snowy owl, of course, is mostly white. They are purer white than predatory mammals like polar bears (''Ursus maritimus'') and Arctic fox (''Vulpes lagopus''). Often when seen in the field, these owls can resemble a pale rock or a lump of snow on the ground. It usually appears to lack ear tufts but very short (and probably vestigial) tufts can be erected in some situations, perhaps most frequently by the female when she is sitting on the nest. The ear tufts measure about and consist of about 10 small feathers. The snowy owl has bright yellow eyes. The head is relatively small and, even for the relatively simply adapted hearing mechanism of a ''Bubo'' owl, the facial disc is shallow and the ear is uncomplicated. 1 male had ear slits of merely on left and on the right. Females are almost invariably more duskily patterned than like-age males. In mature males, the upper parts are plain white with usually a few dark spots on the miniature ear-tufts, about the head and the tips of some primaries and secondaries whilst the underside is often pure white. Despite their reputation for being purely white, only 3 out of 129 Russian museum specimens of adult males showed an almost complete absence of darker spots. The adult female is usually considerably more spotted and often slightly barred with dark brown on the crown and the underparts. Her flight and tail feathers are faintly barred brown while the underparts are white in base color with brown spotting and barring on the flanks and upper breast. In confusingly plumaged snowy owls, the sex can be determined by the shape of wing markings, which manifest as bars more so in females and spots in males.Lind, H. (1993). ''Different ecology in male and female wintering Snowy Owls Nyctea scandiaca L. in Sweden due to colour and size dimorphism''. Ornis Svecica 3 (3–4):147–158. However, the very darkest males and the lightest females are nearly indistinguishable by plumage. On rare occasion, a female can appear almost pure white, as has been recorded in both the field and in captivity.McMorris, A. (2011). ''Snowy Owls: Age, Sex and Plumage''. Presentation Delaware Valley Ornithological Club. There is some evidence that some of the species grow paler with age after maturity.Dementiev, G. P., Gladkov, N. A., Ptushenko, E. S., Spangenberg, E. P., & Sudilovskaya, A. M. (1966). ''Birds of the Soviet Union, vol. 1''. Israel Program for Scientific Translations, Jerusalem. One study's conclusions were that males were usually but not always lighter and that correctly aging is extremely difficult, sometimes individuals either get lighter, darker or do not change their appearance with age. On the other hand, with close study, it is possible to visually identify even individual snowy owls using the pattern of markings on the wing, which can be somewhat unique in each individual. After a fresh moult, some adult females that previously appeared relatively pale newly evidenced dark, heavy markings. On the contrary, some banded individuals over at least four years were observed to have been almost entirely unchanged in the extent of their markings. In another very pale owl, the barn owl (''Tyto alba''), the sexual dimorphism of spotting appears to be driven by genetics while, in snowy owls, environment may be the dictating factor instead.
The chicks are initially grayish white but quickly transition to dark gray-brown in the mesoptile plumage. This type of plumage camouflages effectively against the variously colored lichens that dot the tundra ground. This is gradually replaced by plumage showing dark barring on white. At the point of fledging, the plumage often becomes irregularly mottled or blotched with dark and is mostly solidly dark gray-brown above with white eyebrows and other areas of the face white. Recently fledged young can already be sexed to a semi-reliable degree by the dark marking patterns about their wings.Seidensticker, M. T., D. W. Holt, J. Detienne, S. Talbot & Gray, K. (2011). ''Sexing young Snowy Owls''. Journal of Raptor Research 45 (4):281–289. The juvenile plumage resembles that of adult females but averages slightly darker on average. By their second moult fewer or more broken bars are usually evidenced on the wing. The extent of white and composition of wing patterns become more dimorphic by sex with each juvenile moult, culminating in the 4th or 5th pre-basic moult, wherein the owls are hard to distinguish from mature adults. Moults usually occur from July and September, non-breeding birds moulting later and more extensively, and are never extensive enough to render the owls flightless. Evidence indicates that snowy owls may attain adult plumage at 3 to 4 years of age, but fragmentary information suggests that some males are not fully mature and/or as fully white in plumage that they can attain until the 9th or 10th year.Ridgway, R., & Friedmann, H. (1914). ''The Birds of North and Middle America: A Descriptive Catalog of the Higher Groups, Genera, Species, and Subspecies of Birds Known to Occur in North America, from the Arctic Lands to the Isthmus of Panama, the West Indies and Other Islands of the Caribbean Sea, and the Galapagos Archipelago'' (Vol. 50). US Government Printing Office. Generally speaking, moults of snowy owls occur more quickly than do those of Eurasian eagle-owls.
The toes of the snowy owl are extremely thickly feathered white, while the claws are black. The toe feathers are the longest known of any owl, averaging at , against the great horned owl which has the 2nd longest toe feathers at a mean of Occasionally, snowy owls may show a faint blackish edge to the eyes and have a dark gray cere, though this is often not visible from the feather coverage, and a black bill. Unlike many other whitish birds, the snowy owl does not possess black wingtips, which is theorized to minimize wear-and-tear on the wing feathers in the other whitish bird types. The conspicuously notched primaries of the snowy owl appear to give an advantage over similar owls in long-distance flight and more extensive flapping flight. The snowy owl does have some of the noise-canceling serrations and comb-like wing feathers that render the flight of most owls functionally silent, but they have fewer than most related ''Bubo'' owls. Therefore, in combination with its less soft feathers, the flight of a snowy owl can be somewhat audible at close range. The flight of snowy owls tends to be steady and direct and is reminiscent to some of the flight of a large, slow-flying falcon. Though capable of occasional gliding flight, there is no evidence that snowy owls will soar. It is said that the species seldom exceeds a flying height of around even during passage. While the feet are sometimes described as "enormous", the tarsus is in osteological terms relatively short at 68% the length of those of a Eurasian eagle-owl but the claws are nearly as large, at 89% of the size of those of the eagle-owl. Despite its relatively short length, the tarsus is of similar circumference as in other ''Bubo'' owls. Also compared to an eagle-owl, the snowy owl has a relatively short decurved rostrum, a proportionately greater length to the interorbital roof and a much longer sclerotic ring surrounding the eyes while the anterior opening are the greatest known in any owl. Owls have extremely large eyes which are nearly the same size in large species such as the snowy owl as those of humans. The snowy owl's eye, at about in diameter, is slightly smaller than those of great horned and Eurasian eagle-owls but is slightly larger than those of some other large owls. Snowy owls must be able to see from great distances and in highly variable conditions but probably possess less acute night vision than many other owls. Based on the study of dioptres in different owl species, the snowy owl was determined to have eyesight better suited to long-range perception than to close discrimination, while some related species such as great horned owls could probably more successful perceive closer objects. Despite their visual limits, snowy owls may have up to 1.5 times more visual acuity than humans. Like other owls, snowy owls can probably perceive all colors but cannot perceive ultraviolet visual pigments. Owls have the largest brains of any bird (increasing in sync with the size of the owl species), with the size of the brain and eye related less to intelligence than perhaps to increased nocturnality and predatory behavior.
Size
The snowy owl is a very large owl. They are the largest avian predator of the High Arctic and one of the largest owls in the world. Snowy owls are about the sixth or seventh heaviest living owl on average, around the fifth longest and perhaps the third longest winged.Weidensaul, S. (2015). ''Owls of North America and the Caribbean''. Houghton Mifflin Harcourt. This species is the heaviest and longest winged owl (as well as the second longest) in North America, the second heaviest and longest winged owl in Europe (and third longest) but is outsized in bulk by about 3 to 4 other species in Asia. Despite being sometimes described as of similar size, the snowy owl is somewhat larger in all aspects of average size than the great horned owl while the similarly specialized taiga-dwelling great grey owl (''Strix nebulosa''), is longer in total length and of similar dimensions in standard measurements, but is shorter winged and much less heavy than the snowy owl. In Eurasia, the Eurasian eagle-owl is larger in all standards of measurements than the snowy owl not to mention two additional species each from Africa and Asia that are slightly to considerably heavier on average than the snowy owl.Mikkola, H. (1983). ''Owls of Europe''. T. & AD Poyser. Like most birds of prey, the snowy owl shows reverse sexual dimorphism relative to most non-raptorial birds in that females are larger than males. Sexual dimorphism that favors the female may have some correlation with being able to more effectively withstand food shortages such as during brooding as well as the rigors associated with incubating and brooding. Females are sometimes described as “giant” whereas males appear relatively “neat and compact”. However, the sexual dimorphism is relatively less pronounced compared to some other ''Bubo'' species.
Male snowy owls have been known to measure from in total length, with an average from four large samples of and a maximum length, perhaps in need of verification, of reportedly .Eckert, A. W. (1987). ''The Owls of North America, North of Mexico: All the Species and Subspecies Illustrated in Color and Fully Described''. Gramercy.Parmelee, D. F. (1972). ''Canada's incredible arctic owls''. Beaver no. summer:30–41.Priklonskiy, S.G. (1993). ''Snowy Owl — Nyctea scandiaca (Linnaeus, 1758)''. In: ''Birds of Russia and adjoining regions: Pterocliformes, Columbiformes, Cuculiformes, Strigiformes''. Moscow, p. 258–270. (in Russian).Keith, L.B. (1960). ''Observations of Snowy Owls at Delta, Manitoba''. Can. Field-Nat. 74:106–112. In wingspan, males may range from , with a mean of . In females, total length has been known to range from , with a mean of and an unverified maximum length of perhaps (if so they would have the second longest maximum length of any living owl, after only the great grey owl). Female wingspans have reportedly measured from , with a mean of . Despite one study claiming that snowy owl had the highest wing loading (i.e. grams per square cm of wing area) of any of 15 well-known owl species, more extensive sampling demonstratively illustrated that the wing loading of snowy owls is notably lower than Eurasian eagle- and great horned owls. The conspicuously long-winged profile of a flying snowy owl compared to these related species may cause some to compare their flight profile to a bulkier version of an enormous ''Buteo'' or a large falcon. Body mass in males can average from , with a median of and a full weight range of from six sources.Earhart, C. M., & Johnson, N. K. (1970). ''Size dimorphism and food habits of North American owls''. The Condor, 72(3), 251–264.Kerlinger, P., & Lein, M. R. (1988). ''Causes of Mortality, Fat Condition, and Weights of Wintering Snowy Owls''. Journal of Field Ornithology, 7–12. Body mass in females can average from , with a median of and a full weight range of . Larger than the aforementioned body mass studies, a massive pooled dataset at six wintering sites in North America showed that 995 males averaged at while 1,189 females were found to average .Chang, A. M., & Wiebe, K. L. (2016). ''Body condition in Snowy Owls wintering on the prairies is greater in females and older individuals and may contribute to sex-biased mortality''. The Auk: Ornithological Advances, 133(4), 738–746. Reported weights of down to for males and of for females are probably in reference to owls in a state of starvation.Pitelka, F. A., P. Q. Tomich & Treichel, G. W. (1955). ''Breeding behavior of jaegers and owls near Barrow, Alaska''. Condor 57:3–18. Such emaciated individuals are known to highly impaired and starvation deaths are probably not infrequent in winters with poor food accesses.Ryabitsev, V.K. (2011). ''Birds of the Urals, Ural Region, and Western Siberia: Guide and Identification Key'' (Ural’sk. Univ., Yekterinburg).Golovatin, M.G. & Paskhalniy, S.P. (2005). ''Ptitsy Polyarnogo Urala (Birds of the Polar Urals)'', Ekaterinburg, Siberia.
Standard measurements have been even more widely reported than length and wingspan. The wing chord of males can vary from , averaging from with a median of .Josephson, B. (1980). ''Aging and sexing snowy owls''. Journal of Field Ornithology . 51: 149- 160.Portenko, L. A. (1972). ''Die Schnee-Eule: Nyctea scandiaca'' (Vol. 454). A. Ziemsen. The wing chord of females can vary from , averaging from with a median of . The tail length of males can vary on average from , with a full range of and a median of . The tail length of females can average from , with a full range of and a median of . Data indicates that slightly longer wing chord and tail lengths were reported on average in Russian data than in American research, however the weights were not significantly different in the two regions. Less widely taken measurements include the culmen, which can measure from with a median average of in males and in females, and the total bill length which is from , with an average in both sexes of . Tarsal length in males averages about , with a range of , and averages about , with a range of , in females.
Identification
The snowy owl is certainly one of the most unmistakable owls (or perhaps even animals) in the world. No other species attains the signature white stippled sparsely with black-brown color of these birds, a coloring which renders their bright yellow eyes all the more detectable, nor possesses their obvious extremely long feathering. The only other owl to breed in the High Arctic is the short-eared owl (''Asio flammeus''). Both species inhabit open country, overlap in range and are often seen by day, but the short-eared is much smaller and more tan or straw-colored in coloration, with streaked brown on chest. Even the palest short-eared owls conspicuously differ and are darker than the snowy owl; additionally the short-eared most often hunts in extended flights.Pyle, P. (1997). ''Identification Guide to North American Birds, Part I: Columbidae to Ploceidae''. Slate Creek Press, Bolinas, CA, USA. More similar owls such as the Eurasian eagle-owl and the great horned owl attain a fairly pale, sometimes white-washed look in their northernmost races. These species do not normally breed nearly as far north as snowy owls but overlaps certainly do occur when snowy owls when the latter owl sometimes comes south in winter. However, even the most pale great horned and Eurasian eagle-owls are still considerably more heavily marked with darker base colors than snowy owls (the whitest eagle-owls are paler than the whitest great horned owls), possess much larger and more conspicuous ear tufts and lack the bicolored appearance of the darkest snowy owls. While the great horned owl has yellow eyes like the snowy owl, the Eurasian eagle-owl tends to have bright orange eyes. The open terrain habitats normally used by wintering snowy owls are also distinct from the typical edge and rocky habitats usually favored by the great horned and Eurasian eagle-owls, respectively.
Vocalizations
The snowy owl differ in their calls from other ''Bubo'' owls, with a much more barking quality to their version of a hooting song. Perhaps as many as 15 different calls by mature snowy owls have been documented.Evans, D. L. (1980). ''Vocalizations and territorial behavior of wintering Snowy Owls''. Am. Birds 34: 748–749.Sutton, G. M. (1932). ''The exploration of Southampton Island. Part II, Zoölogy. Section 2.-The birds of Southampton Island''. Memoirs of the Carnegie Museum 12 (2):1–275. The main vocalization is a monotonous sequence that normally contains 2–6 (but occasionally more), rough notes similar to the rhythm of a barking dog: ''krooh krooh krooh krooh''... The call may end with an emphatic ''aaoow'', which is somewhat reminiscent of the deep alarm call of a great black-backed gull (''Larus marinus''). They will call mainly from a perch but also sometimes do so in flight. The ''krooh'' call of the male snowy owl may perform multiple functions such as competitive exclusion of other males and advertising to females.Taylor, P.S. (1973). ''Breeding behaviour of the Snowy Owl''. Living Bird. 12: 137–154. The calls of this species may carry exceptionally far in the thin air of Arctic, certainly over more than , and maybe even to as much away. The female has a similar call to male but can be higher-pitched and/or more guttural as well as single notes which are often disyllabic, ''khuso''. Female snowy owls have also been known to utter chirps and high screaming notes, similar to those of the nestlings. Both sexes may at times give a series of clucking, squeals, grunts, hisses and cackles, perhaps such as in circumstances when they are excited. The alarm call is a loud, grating, hoarse ''keeea''. Another raspier bark is recorded, sometimes called a "watchman's rattle" call, and may be transcribed as ''rick, rick, rick'', ''ha, how, quack, quock'' or ''kre, kre, kre, kre, kre''. A female attacking to protect her nest was recorded to let out a crowed ''ca-ca-oh'' call, whilst other owls attacking to protect the nest did a loud version of the typical call while circling before dropping down.Sutton, G. M. & Parmelee, D. F. (1956). ''Breeding of the Snowy Owl in southeastern Baffin Island''. Condor 58:273–282. They may also clap their beak in response to threats or annoyances. While called clapping, it is believed this sound may actually be a clicking of the tongue, not the beak. Though largely only vocal in the breeding season, leading to some erroneous older accounts describing the snowy owl as completely silent, some vocalizations have been recorded in winter in the northern United States. Initially, the young of the snowy owl have a high pitched and soft begging call which develops into a strong, wheezy scream at around 2 weeks. At the point when the young owls leave the nest around 3 weeks, the shrill squeals they emit may allow the mothers to locate them.Parmelee, D. (1992). ''Snowy Owl (Nyctea scandiaca)''. No. 10 in: Poole et al. (1992–1993).
Distribution and habitat
Breeding range
The snowy owl is typically found in the northern circumpolar region, where it makes its summer home north of latitude 60° north though sometimes down to 55 degrees north. However, it is a particularly nomadic bird, and because population fluctuations in its prey species can force it to relocate, it has been known to breed at more southerly latitudes. Although the total breeding range includes a little over , only about have a high probability of breeding, i.e. breeding at no more than 3–9-year intervals. Snowy owls nest in the Arctic tundra of the northernmost stretches of Alaska, Northern Canada, and Eurosiberia. Between 1967 and 1975, snowy owls bred on the remote island of Fetlar in the Shetland Isles north of mainland Scotland, discovered by the Shetland RSPB warden, Bobby Tulloch. Females summered as recently as 1993, but their status in the British Isles is now that of a rare winter visitor to Shetland, the Outer Hebrides and the Cairngorms. Older records show that the snowy owls may have once semi-regularly bred elsewhere in the Shetlands. They range in northern Greenland (mostly Peary Land) and, rarely in "isolated parts of the highlands", Iceland.Manniche, A. L. V. (1910). ''The terrestrial mammals and birds of east Greenland; biological observations''. Medd. Grønland 45:1–200. Thence, they are found breeding at times across northern Eurasia such as in Spitsbergen and western and northern Scandinavia. In Norway, they normally breed in Troms og Finnmark and seldom down as far south as Hardangervidda and in Sweden perhaps down to the Scandinavian Mountains while breeding is very inconsistent in Finland.Barth, E. (1949). ''Norwegian Animal Life. Volume 2. Birds''.Jacobsen, K. O. (2005). ''Snøugle (Bubo Scandiacus) Norge. Hekkeforekomster i perioden 1968–2005''. Hekkeforekomster i perioden, 2005. They also range in much of northern Russia, including northern Siberia, Anadyr, Koryakland, Taymyr Peninsula, Yugorsky Peninsula, Sakha (especially the Chukochya River) and Sakhalin. Breeding have also been reported sporadically to the south in the Komi Republic and even the Kama River in southern Perm Krai. Although considered part of the regular range, the last breeding by snowy owls in the Kola Peninsula was not since the early 1980s; similarly, breeding maps show the species in Arkhangelsk Oblast and the Pay-Khoy Ridge but no breeding records known in at least 30 years in either. They range throughout most of the Arctic isles of Russia such as Novaya Zemlya, Severnaya Zemlya, New Siberian Islands, Wrangel Island, Commander and Hall Islands. In North America, the breeding range has been known in modern times to include the Aleutians (i.e. Buldir and Attu) and much of northern Alaska, most frequently from the Arctic National Wildlife Refuge to Utqiaġvik, and more sporadically down along the coastal-western parts such as through Nome, Hooper Bay, the Yukon Delta National Wildlife Refuge, and rarely even south to the Shumagin Islands. The snowy owl may breed extensively in northern Canada, largely making its home in the Arctic Archipelago. Their Canadian breeding range can include broadly Ellesmere Island up to Cape Sheridan, north coastal Labrador, the northern Hudson Bay, perhaps all of Nunavut (especially the Kivalliq Region), northeastern Manitoba, both most of northern mainland and insular Northwest Territories (including the delta of the Mackenzie River) and northern Yukon Territory (where breeding is mostly confined to Herschel Island).Parmelee, D. F., & MacDonald, S. D. (1960). ''The birds of west-central Ellesmere Island and adjacent areas (No. 63)''. Department of Northern Affairs and National Resources. Since breeding and distribution is very small, local and inconsistent in northern Europe, northern Canada and northern Alaska represent the core part of the breeding range for snowy owls along with several parts of northern and northeastern/coastal Russia.
Regular wintering range
During the wintering, many snowy owls leave the dark Arctic to migrate to regions further south. Southern limits of the regular winter range are difficult to delineate given the inconsistency of appearances south of the Arctic. Furthermore, not infrequently, many snowy owls will overwinter somewhere in the Arctic through the winter, though seldom appear to do so in the same sites where they have bred. Due in no small part to the difficulty and hazardousness of observation for biologists during these harsh times, there is very limited data on overwintering snowy owls in the tundra, including how many occur, where they winter and what their ecology is at this season. The regular wintering range has at times been thought to include Iceland, Ireland and Scotland and across northern Eurasia such as southern Scandinavia, the Baltics, central Russia, southwestern Siberia, Sakhalin southern Kamchatka and, rarely, north China and sometimes the Altai Republic. In North America, they occasionally regularly winter in the Aleutian island chain and do so broadly and with a fair amount of consistency in much of southern Canada, from British Columbia to Labrador.Godfrey, W. E. (1986). ''The Birds of Canada''. Revised Edition. National Museums of Canada, Ottawa, ON, Canada. Recent research has indicated that snowy owls regularly winter in several of the northern seas during wintertime, following the leads of sea ice as perching sites and presumably hunting mostly seabirds in polynyas.Therrien, J. F., Gauthier, G., & Bêty, J. (2011). ''An avian terrestrial predator of the Arctic relies on the marine ecosystem during winter''. Journal of Avian Biology, 42(4), 363–369. In February 1886, a snowy owl landed on the rigging of the Nova Scotia steamship ''Ulunda'' on the edge of the Grand Banks of Newfoundland, over from the nearest land. It was captured and later preserved at the Nova Scotia Museum.Gross, A. O. (1947). ''Cyclic invasions of the snowy owl and the migration of 1945–1946''. The Auk, 64(4), 584–601. Surprisingly, some studies have determined that after a high lemming year in North America, a higher percentage of snowy owls were using marine environments rather than inland ones.
Irruptive range
Large winter irruptions at temperate latitudes are thought to be due to good breeding conditions resulting in more juvenile migrants. These result in irruptions occurring further south than the typical snowy owl range in some years. They have been reported, as well as in all northerly states in the contiguous states, as far south as the Georgia, Kentucky, South Carolina, nearly all the Gulf Coast of the United States, Colorado, Nevada, Texas, Utah, California and even Hawaii.American Ornithologists' Union (1957). ''Check-list of North American Birds, 5th edition''. American Ornithologists' Union, Washington, DC, USA. In January 2009, a snowy owl appeared in Spring Hill, Tennessee, the first reported sighting in the state since 1987. Also notable is the mass southern migration in the winter of 2011/2012, when thousands of snowy owls were spotted in various locations across the United States. This was then followed by an even larger mass southern migration in 2013/2014 with the first snowy owls seen in Florida for decades. The nature of irruptions is less well-documented in Eurasia, in part due to the paucity of this owl in the European side, but accidental occurrence, presumably during irruptions, has been described in the Mediterranean area, France, Crimea, the Caspian part of Iran, Kazakhstan, northern Pakistan, northwestern India, Korea and Japan. Stragglers may too turn up as far south as the Azores and Bermuda.
Habitat
Snowy owls are one of the best known inhabitants of the open Arctic tundra. Frequently, the earth in snowy owl breeding grounds is covered with mosses, lichens and some rocks. Often the species preferentially occurs in areas with some rising elevation such as hummocks, knolls, ridges, bluffs and rocky outcrops. Some of these rises in the tundra are created by glacial deposits. The ground is usually rather dry in tundra but in some areas of the southern tundra can also be quite marshy. Not infrequently, they will also use areas of varied coastal habitat, often tidal flats, as a breeding site.Murie, O. J. (1929). ''Nesting of the snowy owl''. The Condor, 31(1), 3–12. Breeding sites are usually at low elevations, usually less than above sea level, but when breeding to the south in inland mountains, such as in Norway, they may nest at as high as . Outside the breeding season, snowy owls may habituate nearly any open landscape. Typically wintering sites are rather windswept with meager cover. These open areas can include those such as coastal dunes, other coastal spots, lakeshores, islands, moorlands, steppes, meadows, prairies, other extensive grasslands and rather shrubby areas of the Subarctic. These may be favored due to their vague similarity to the flat openness of the tundra.Fuller, M., Holt, D. & Schueck, L. (2003). ''Snowy Owl movements: Variation on the migration theme''. Edited by P. Berthold, E. Gwinner and E. Sonnenschein, Avian migration. Berlin: Springer-Verlag. Manmade open sites are now perhaps even more used than natural ones, often agricultural fields and rangeland, as well as large areas of cleared forests.Kerlinger, P., Lein, M.R. & Sevick, B.J. (1985). ''Distribution and population fluctuations of wintering Snowy Owls (Nyctea scandiaca) in North America''. Canadian Journal of Zoology. 63(8): 1829–1834.Doyle, F. I., Therrien, J. F., Reid, D. G., Gauthier, G., & Krebs, C. J. (2017). ''Seasonal movements of female Snowy Owls breeding in the western North American Arctic''. Journal of Raptor Research, 51(4), 428–438. During irruption years when they are found in the Northeastern United States, juveniles frequent developed areas including urban areas and golf courses, as well as the expected grasslands and agricultural areas that older birds primarily use. On the plains of Alberta, observed snowy owls spent 30% of their time in stubble-fields, 30% in summer fallow, 14% in Hayfield and the remainder of the time in pasture, natural grasslands and sloughs. The agricultural areas, large untouched by the farmers in winter, may have had more concentrated prey than the others in Alberta.Lein, M.R. & Webber, G.A. (1979). ''Habitat selection by wintering Snowy Owls (Nyctea scandiaca)''. Canadian Field-Naturalist. 93(2): 176–178. Perhaps the most consistently attractive habitat in North America to wintering snowy owls in modern times may be airports, which not only tend to have the flat, grassy characteristics of their preferred habitats but also by winter host a particular diversity of prey, both pests which rely on humans as well as wildlife attracted to the extensively grassy and marshy strips that dot the large airport vicinities. For example, Logan International Airport in Massachusetts has one relatively one of the most reliable annual populations known in the United States in winter.Smith, N. (1997). ''Observations of wintering Snowy Owls (Nyctea scandiaca) at Logan Airport, East Boston, Massachusetts from 1981 to 1997''. In: ''Biology and conservation of owls of the Northern Hemisphere: 2nd International Symposium'', edited by J. R. Duncan, D. H. Johnson and T. H. Nicholls, 591–596. St. Paul: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. All ages spend a fair amount of their time over water in the Bering Sea, the Atlantic Ocean and even the Great Lakes, mostly on ice floes. These marine and ocean-like freshwater areas were observed to account for 22–31% of habitat used in 34 radio-tagged American snowy owls over two irruptive years, with the tagged owls occurring a mean of from the nearest land (while 35–58% used the expected preferred habitats of grassland, pasture and other agriculture).
Behavior
Snowy owls may be active to some extent at both day, from dawn to dusk, and night. Snowy owls have been seen to be active even during the very brief winter daytime in the northern winter. During the Arctic summer, snowy owls may tend to peak in activity during the twilight that is the darkest time available given the lack of full nightfall. Reportedly, the peak time of activity during summer is between 9:00 pm and 3:00 am in Norway.Hagen, Y. (1960). ''The Snowy Owl on Hardangervidda in the Summer of 1959''. Papers of The Norwegian State Game Research. 2, No. 7. The peak time of activity for those owls that once nested on Fetlar was reported between 10:00 and 11:00 pm.Tulloch, R. J. (1968). ''Snowy Owls breeding in Shetland in 1967''. British Birds 61:119–132. According to one authority, the least active times are at noon and midnight. As days become longer near autumn in Utqiaġvik, the snowy owls in the tundra become more active around nightfall and can often be seen resting during the day, especially if it is raining. During winter in Alberta, snowy owls were tracked in the daytime, despite being also active at night (as they were deemed too difficult to track). In the study, they were most active from 8:00–10:00 am and 4:00–6:00 pm and often rested mostly from 10:00 am to 4:00 pm. The owls were perched for 98% of observed daylight and seemed to time their activity to peak times for rodents. The variation of activity is probably in correspondence with their primary prey, the lemmings, and like them, the snowy owl may be considered cathermal. This species can withstand extremely cold temperatures, having been recorded in temperatures as low as minus 62.5 degrees Celsius with no obvious discomfort and also withstood a 5-hour exposure to minus 93 degrees Celsius but may have struggled with oxygen consumption by the end of this period. The snowy owl has perhaps the second lowest thermal conduction to the plumage on average of any bird after only the Adelie penguin (''Pygoscelis adeliae'') and rivals the best insulated mammals, such as Dall sheep (''Ovis dalli'') and Arctic fox, as the best insulated polar creature.Gessaman, J. A. (1972). ''Bioenergetics of the snowy owl (Nyctea scandiaca)''. Arctic and Alpine Research, 4(3), 223–238. Presumably as many as 7 rodents would need to be eaten daily to survive an extremely cold winter's day. Adults and young both have been seen to shelter behind rocks to shield themselves from particularly harsh winds or storms. Snowy owls often spending a majority of time on the ground, perched mostly on a slight rise of elevation. It has been interpreted from the morphology of their skeletal structure (i.e. their short, broad legs) that snowy owls are not well-suited to perching extensively in trees or rocks and prefer a flat surface to sit upon. However, they may perch more so in winter though do so only mainly when hunting, at times on hummocks, Fenceposts, telegraph poles by roads, radio and transmission towers, Haystacks, chimneys and the roofs of houses and large buildings. Rocks may be used as perches at times in all seasons. Though often relatively sluggish owls, like most related species, they are capable of sudden dashing movements in various contexts. Snowy owls can walk and run quite quickly, using outstretched wings for balance if necessary. This owl flies with fairly rowing wingbeats, occasionally interrupted by gliding on stretched wings. The flight is fairly buoyant for a ''Bubo'' owl.